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Quantification of forage particle length and its effect on intake and chewing behavior in dairy.. 1985

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c QUANTIFICATION OF FORAGE PARTICLE LENGTH AND ITS EFFECT ON INTAKE AND CHEWING BEHAVIOR IN DAIRY CATTLE by ALAN STANLEY VAAGE B.Sc, The U n i v e r s i t y of B r i t i s h Columbia, 1982 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Animal Science) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1985 (c) Alan Stanley Vaage, 1985 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. ^Clan S. "V^»g4 Department of Animal Science The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date March 7, 1986 DE-6(3/81) ABSTRACT A method for the quantitation of the p a r t i c l e length d i s t r i b u t i o n i n processed forage was developed, tested, and used to investigate the e f f e c t of processing method and forage type on p a r t i c l e length d i s t r i b u t i o n . The same method was also used to investigate the e f f e c t of forage p a r t i c l e length on voluntary feed intake (VFI) and chewing behavior i n dairy c a t t l e . A simple v i b r a t i n g tray forage p a r t i c l e separator (FPS) was constucted to separate forage p a r t i c l e s on the basis of length alone. Although not completely accurate, the separator produced repeatable r e s u l t s i n separating forage p a r t i c l e s into s i x t h e o r e t i c a l length f r a c t i o n s (<3.3, 3.3-8.25, 8.25-16.5, 16.5-33.0, 33.0-66.0 and >66.0 mm). Cumulative sample weight undersize of separated orchardgrass hay was f i t t e d by regression to a l i n e a r and two exponential equations, a lognormal d i s t r i b u t i o n , and a modified Weibull function. Only the Weibull function c l o s e l y f i t these separation data. The median p a r t i c l e length (MPL) could be predicted by the inverse of the B parameter of the modified Weibull function while the use of the C parameter (named the C o e f f i c i e n t of Spread (CS)) was proposed as a measure of the spread of p a r t i c l e lengths around a given median. A l f a l f a and low and high q u a l i t y orchardgrass hays were hammered through a 12.7 mm screen and chopped at 3 t h e o r e t i c a l lengths of cut (3.18, 6.35 and 9.53 mm) and separated on the FPS to determine the respective dry matter (DM), crude p r o t e i n (CP) and a c i d detergent f i b e r (ADF) MPL and CS. The MPL were based on the weight of each n u t r i e n t c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on the FPS. D i f f e r e n t forages, processed by the same method, produced s i g n i f i c a n t l y d i f f e r e n t (P < 0.05) DM, CP and ADF MPL, and CS. i i Furthermore, the differences i n DM MPL and CS between forages were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05) from those f o r CP and ADF. There were also s i g n i f i c a n t differences (P < 0.05) between the DM and CP MPL, and the DM and ADF MPL, within each forage type. Twelve l a c t a t i n g H o l s t e i n cows were fed orchardgrass hay chopped to two d i f f e r e n t MPL (7.3 and 18.1 mm) at two forage to concentrate r a t i o s (40:60 and 60:40). The p a r t i c l e length of the forage d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) VFI or chewing behavior. Increasing the forage to concentrate r a t i o s i g n i f i c a n t l y (P < 0.05) decreased voluntary feed intake, increased the time spent chewing per kg of feed intake during eating and rumination and increased the number of b o l i regurgitated per kg of feed intake during rumination. When dairy steers were fed timothy-brome hay chopped to 4 MPL (5.2, 9.0, 13.3 and 20.0 mm) at a 60:40 forage to concentrate r a t i o , an increase i n the MPL of the forage i n the d i e t s i g n i f i c a n t l y (P < 0.05) decreased the time spent i d l e , increased the time spent ruminating and the t o t a l time spent chewing (eating plus rumination), and increased the number of b o l i regurgitated per kg of feed intake. These e f f e c t s of forage MPL on chewing behavior were d i r e c t l y r e l a t e d to the logarithm of the forage MPL. Increasing the MPL of the forage s i g n i f i c a n t l y decreased (P < 0.05) the time spent chewing per bolus regurgitated during rumination. i i i TABLE OF CONTENTS page ABSTRACT i i LIST OF TABLES v LIST OF FIGURES I v i i i ACKNOWLEDGEMENT x GENERAL INTRODUCTION 1 CHAPTER 1: Descr i p t i o n of the p a r t i c l e length d i s t r i b u t i o n of chopped forage using a simple v i b r a t i n g tray Forage P a r t i c l e Separator and a modified Weibull-type function 4 Introduction 4 Li t e r a t u r e Review 6 Materials and Methods 24 Results and Discussion 33 Summary 63 CHAPTER 2: The e f f e c t of processing method and forage type on the p a r t i c l e length d i s t r i b u t i o n of DM, CP and ADF i n processed forage 64 Introduction 64 L i t e r a t u r e Review 66 Materials and Methods 69 Results and Discussion 73 Summary 92 CHAPTER 3: The e f f e c t of forage p a r t i c l e length and forage to concentrate r a t i o on intake and chewing behavior i n dairy c a t t l e 93 Introduction 93 L i t e r a t u r e Review 95 Materials and Methods 116 Results 126 Discussion 138 Summary 144 GENERAL SUMMARY AND CONCLUSIONS 146 LITERATURE CITED 150 APPENDICES 158 i v LIST OF TABLES page TABLE I: ASAE (1969b) example c a l c u l a t i o n s f o r the determination of the Modulus of Fineness of ground feedstuffs by s i e v i n g 14 TABLE I I : ASAE (1969b) example c a l c u l a t i o n s f o r the determination of the Modulus of Uniformity of ground feedstuffs by s i e v i n g 15 TABLE I I I : Average percent of sample weight (n = 4) of hand chopped a l f a l f a hay c o l l e c t e d i n each p a r t i c l e length f r a c t i o n a f t e r each of three separation runs on the Forage P a r t i c l e Separator 34 TABLE IV: P a r t i c l e length d i s t r i b u t i o n s (percent of sample weight) of mature orchardgrass hay, chopped at three t h e o r e t i c a l lengths of cut (TLC), determined by the FPS and by v i s u a l (VIS) separation 36 TABLE V: Percent weight of p a r t i c l e s c o l l e c t e d i n each t h e o r e t i c a l p a r t i c l e length f r a c t i o n on the Forage P a r t i c l e Separator (FPS) that were c o r r e c t l y and i n c o r r e c t l y s i z e d 37 TABLE VI: Percent weight of sample forage p a r t i c l e s of the given actual ranges of p a r t i c l e length that were c o r r e c t l y and i n c o r r e c t l y s i z e d by the Forage P a r t i c l e Separator 39 TABLE VII: Percent weight of a l l p a r t i c l e s f a l l i n g into the corre c t tray (T Q) and into trays before (-) and a f t e r (+) the corr e c t tray on the FPS f o r mature orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC) 40 TABLE VIII: P a r t i c l e length d i s t r i b u t i o n s (percent of sample weight) of mature orchardgrass hay, chopped at three t h e o r e t i c a l lengths of cut (TLC), determined by the Forage P a r t i c l e Separator(FPS) and by v i s u a l (VIS) separation a f t e r c a l i b r a t i o n of the FPS 42 TABLE IX: Percent weight of p a r t i c l e s , c o l l e c t e d i n each t h e o r e t i c a l p a r t i c l e length f r a c t i o n on the Forage P a r t i c l e Separator (FPS) that were c o r r e c t l y and i n c o r r e c t l y s i z e d a f t e r c a l i b r a t i o n 42 v v i TABLE XIX: Deviation between the DM and CP, and DM and ADF median p a r t i c l e lengths (mm) of the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC) 84 TABLE XX: DM, CP and ADF c o e f f i c i e n t s of spread of the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC) 88 TABLE XXI: P a r t i c l e length d i s t r i b u t i o n (% sample wt.) and d i s t r i b u i o n parameters of the short and long chopped orchardgrass hay 126 TABLE XXII: Nutrient content (%, DM basis) of the concentrate and short and long chopped orchardgrass hay used i n the experiment 127 TABLE XXIII: E f f e c t of forage median p a r t i c l e length on intake and chewing c h a r a c t e r i s t i c s 128 TABLE XXIV: E f f e c t of forage to concentrate r a t i o on intake and chewing c h a r a c t e r i s t i c s 128 TABLE XXV: E f f e c t of forage to concentrate r a t i o and forage median p a r t i c l e length (mm) on intake and chewing c h a r a c t e r i s t i c s 129 TABLE XXVI: P a r t i c l e Length d i s t r i b u t i o n s (% sample wt.) and d i s t r i b u t i o n parameters of the chopped timothy-brome hay 130 TABLE XXVII: Nutrient content (%, DM basis) of the concentrate and the four lengths (mm) of chopped timothy-brome hay used i n the experiment 131 TABLE XXVIII: Nutrient content (%, DM basis) of the di e t a r y treatments (40% concentrate with 60% timothy-brome hay chopped at four median p a r t i c l e lengths) 132 TABLE XXIX: E f f e c t of forage median p a r t i c l e length (mm) on intake and chewing c h a r a c t e r i s t i c s 133 TABLE XXX: Regression (Y = a + blogX) and BW0-75 covariable c o e f f i c i e n t s f o r the e f f e c t of forage median p a r t i c l e length on chewing and rumination c h a r a c t e r i s t i c s 134 v i i L I S T OF F I G U R E S page F I G U R E 1 : F o r a g e P a r t i c l e S e p a r a t o r 25 F I G U R E 2 : A r r a n g e m e n t o f 4 g r o u p s o f s u b s a m p l i n g b o x e s f o r o b t a i n i n g 3 r e p r e s e n t a t i v e s a m p l e s o f a c h o p p e d f o r a g e 29 F I G U R E 3: P l o t s o f F P S s e p a r a t i o n d a t a f o r l o w q u a l i t y o r c h a r d g r a s s h a y c h o p p e d a t a T L C o f 3 . 1 8 mm s h o w i n g t h e f i t o f t h e o b s e r v e d p o i n t s t o t h e p r e d i c t e d l i n e ( a ) a n d t h e d i s t r i b u t i o n o f r e s i d u a l s ( b ) u s i n g t h e r e g r e s s i o n e q u a t i o n Y = a + b X 47 F I G U R E 4 : P l o t s o f F P S s e p a r a t i o n d a t a f o r l o w q u a l i t y o r c h a r d g r a s s h a y c h o p p e d a t a T L C o f 3 . 1 8 mm s h o w i n g t h e f i t o f t h e o b s e r v e d p o i n t s t o t h e p r e d i c t e d l i n e ( a ) a n d t h e d i s t r i b u t i o n o f r e s i d u a l s ( b ) u s i n g t h e r e g r e s s i o n e q u a t i o n Y = a + b l o g X 4 8 F I G U R E 5: P l o t s o f F P S s e p a r a t i o n d a t a f o r l o w q u a l i t y o r c h a r d g r a s s h a y c h o p p e d a t a T L C o f 3 . 1 8 mm s h o w i n g t h e f i t o f t h e o b s e r v e d p o i n t s t o t h e p r e d i c t e d l i n e ( a ) a n d t h e d i s t r i b u t i o n o f r e s i d u a l s ( b ) u s i n g t h e r e g r e s s i o n e q u a t i o n l o g Y = a + b l o g X 49 F I G U R E 6: P l o t s o f F P S s e p a r a t i o n d a t a f o r l o w q u a l i t y o r c h a r d g r a s s h a y c h o p p e d a t a T L C o f 3 . 1 8 mm s h o w i n g t h e f i t o f t h e o b s e r v e d p o i n t s t o t h e p r e d i c t e d l i n e ( a ) a n d t h e d i s t r i b u t i o n o f r e s i d u a l s ( b ) u s i n g t h e r e g r e s s i o n e q u a t i o n P r o b i t Y = a + b l o g X 50 F I G U R E 7 : P l o t s o f F P S s e p a r a t i o n d a t a f o r l o w q u a l i t y o r c h a r d g r a s s h a y c h o p p e d a t a T L C o f 3 . 1 8 mm s h o w i n g t h e f i t o f t h e o b s e r v e d p o i n t s t o t h e p r e d i c t e d l i n e ( a ) a n d t h e d i s t r i b u t i o n o f r e s i d u a l s ( b ) u s i n g t h e m o d i f i e d W e i b u l l f u n c t i o n 5 1 F I G U R E 8: C h a n g e s i n s h a p e o f t h e m o d i f i e d W e i b u l l c u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n w i t h v a r i o u s B a n d C p a r a m e t e r v a l u e s w h e n " b a s e e " i s u s e d i n t h e e q u a t i o n 56 F I G U R E 9: C h a n g e s i n s h a p e o f t h e m o d i f i e d W e i b u l l c u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n w i t h v a r i o u s B a n d C p a r a m e t e r v a l u e s w h e n " b a s e 2 " i s u s e d i n t h e e q u a t i o n 57 F I G U R E 1 0 : C h a n g e s i n s h a p e o f t h e m o d i f i e d W e i b u l l c u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n g i v e n a f i x e d B p a r a m e t e r v a l u e a n d t h r e e C p a r a m e t e r v a l u e s w h e n " b a s e 2 " i s u s e d i n t h e e q u a t i o n 59 v i i i F I G U R E 1 1 : Changes i n shape of the modified Weibull p r o b a b i l i t y density d i s t r i b u t i o n given a f i x e d B parameter value and three C parameter values when "base 2" i s used i n the equation F I G U R E 1 2 : Plot of the average observed values and predicted regression l i n e s (Y = a + blogX) f o r the r e l a t i o n s h i p between crude p r o t e i n content (Y) and p a r t i c l e length (X) i n processed a l f a l f a (ALF) and high (OGH) and low (OGL) q u a l i t y orchardgrass hays 60 74 F I G U R E 1 3 : Plot of the average observed values and predicted regression l i n e s (Y = a + blogX) f o r the r e l a t i o n s h i p between a c i d detergent f i b e r content (Y) and p a r t i c l e length (X) i n processed a l f a l f a (ALF) and high (OGH) and low (OGL) q u a l i t y orchardgrass hays 75 F I G U R E 1 4 : Dairy c a t t l e i n stanchion s t a l l s i n research area during the monitoring of chewing behavior 117 F I G U R E 1 5 : Pneumatic device of the chewing monitor f o r producing pressure impulses from jaw movement 120 F I G U R E 1 6 : Chewing monitor h a l t e r with pneumatic device and pressure transducer mounted 121 F I G U R E 1 7 : Chewing monitor " s i l i c o n chip" pressure transducer mounted i n i t s s t e e l housing 122 F I G U R E 1 8 : Plot of observed values and predicted regression l i n e s (Y = a + blogX) f o r the r e l a t i o n s h i p between the times animals spent i d l e and chewing per kg intake (Y) and the median p a r t i c l e length of a timothy-bromegrass hay chopped to 4 median p a r t i c l e lengths (X) when the hay was fed i n a 60% forage, 40% concentrate r a t i o n 136 F I G U R E 1 9 : Plot of observed values and predicted regression l i n e (Y = a + blogX) f o r the r e l a t i o n s h i p between the number of b o l i regurgitated during rumination per kg of intake (Y) and median forage p a r t i c l e length (X), and the e f f e c t of median p a r t i c l e length on time spent chewing per bolus regurgitated when timothy-bromegrass hay was chopped to 4 median p a r t i c l e lengths and fed i n a 60% forage, 40% concentrate r a t i o n 137 ix ACKNOWLEDGEMENT F i r s t and foremost the author i s deeply g r a t e f u l and indebted to Dr. J . A. Shelford for g i v i n g him the opportunity to pursue the research described herein, f o r h i s much tested patience, and f o r the support, guidance, and f i n a n c i a l assistance he has given to the author during the supervision of t h i s t h e s i s . S pecial acknowledgement and thanks i s given to Maciek Kowalski for h i s exhaustive assistance during the running of the steer t r i a l and to G i l l e s Galzy for the development and construction of e l e c t r i c a l components that were required to monitor chewing a c t i v i t y of c a t t l e . The author i s also g r a t e f u l to Cheryl McColl and S y l v i a Leung for t h e i r assistance during the monitoring of chewing behavior and to Ted Cathcart, Paul W i l l i n g , William ( B i l l ) Slack and the s t a f f i n the Dairy Unit who a s s i s t e d i n the care of the animals, running of experiments and procurement of supplies. The author also thanks the Natural Sciences and Engineering Research Council f o r personal f i n a n c i a l support. F i n a l l y , s p e c i a l thanks to my wife, Helene, for her assistance i n typing part of t h i s manuscript, f o r a s s i s t i n g with experiments and, e s p e c i a l l y , f or moral support. x GENERAL INTRODUCTION A lack of f i b r e i n the d i e t of ruminants can lead to disorders such as f a t cow syndrome, abomasal u l c e r s , a c i d o s i s , l i v e r abscesses, displaced abomasums, rumenitis, and low f a t content i n the milk of l a c t a t i n g dairy cows (Sudweeks and Ely, 1979). To prevent these disorders, the National Research Council (National Research Council, 1978) has recommended that di e t s fed to l a c t a t i n g dairy cows should contain a minimum of 17% crude f i b e r . Research, however, has shown that excessive reduction of p a r t i c l e s i z e i n forages otherwise adequate i n "chemical f i b e r " components (eg. crude f i b e r , n e u t r a l detergent f i b e r and a c i d detergent f i b e r ) can reduce or even eliminate the effectiveness of the f i b e r i n preventing the disorders l i s t e d above. For t h i s reason, Jorgensen et a l . (1978) recommended the feeding of a given amount of long hay i n the r a t i o n s of dairy c a t t l e . However, the feeding of forages i n a long form as a large proportion of the d i e t can have an i n h i b i t o r y e f f e c t on voluntary feed intake and, therefore, can decrease p r o d u c t i v i t y . The p a r t i c l e s i z e of f e e d s t u f f s , and e s p e c i a l l y that of forages, has been shown to have a d i r e c t e f f e c t on the d i g e s t i o n process and feed u t i l i z a t i o n i n ruminants. Feedstuffs entering the rumen are subjected to microbial digestion, the products of which are absorbed through the rumen walls and i n t e s t i n a l t r a c t . However, a v a r i a b l e proportion of a given feedstuff, predominantly the f i b e r f r a c t i o n , i s e i t h e r i n d i g e s t i b l e or only slowly digested i n the rumen. These undigested residues can only leave the rumen by passage through the reticulo-omasal o r i f i c e . The passage of these undigested or i n d i g e s t i b l e residues from the rumen, however, i s l i m i t e d by the p h y s i c a l s i z e of the p a r t i c l e s . This r e s t r i c t i o n to passage a f f e c t s -1- rumen f i l l which, in turn, has an inhibitory effect on voluntary feed intake. The reduction of the particle size and the subsequent passage of the undigested residue from the rumen is primarily f a c i l i t a t e d by chewing activity during eating and ruminating. Therefore the monitoring of chewing behavior has been used to study the effect of reducing the particle size of forage fed to ruminants on forage u t i l i z a t i o n and as a measure of the fibrousness of the feed. Research has shown that the reduction of the particle size of forages fed to ruminants can have a direct effect on increasing voluntary feed intake by increasing the rate of passage of undigested residues from the rumen. Even though the increased rate of passage usually results in a concomitant decrease in d i g e s t i b i l i t y an increased productivity can be realized from higher intake levels. Unfortunately, the incremental effect of a decrease in forage particle size on increasing intake and rate of passage is not consistent over the f u l l range of applicable particle sizes and between forage types. There appears to be no difference in u t i l i z a t i o n between most forages fed in a long or coarsely chopped form. Fine chopping and coarse grinding of more fibrous or mature forages w i l l usually enhance voluntary feed intake, whereas l i t t l e effect may be seen when feeding similarly processed good quality forages. Fine grinding of most forages, however, w i l l generally result in the disappearance of normal rumination behavior and an increase in the incidence of nutritional disorders. Therefore, there appears to be a relationship between the chemical fiber content and the particle size of feedstuffs fed to ruminants in providing a minimum level of "physical fiber" sufficient to prevent digestive disorders but not limit intake and productivity. Whereas the surface area of feedstuff -2- p a r t i c l e s may have a d i r e c t e f f e c t on microbial digestion, i t i s l i k e l y that the passage of p a r t i c l e s from the rumen i s u l t i m a t e l y l i m i t e d by the l a r g e s t dimension of the p a r t i c l e s . Consequently, i t would be b e n e f i c i a l to quantify the e f f e c t of forage p a r t i c l e length on intake and d i g e s t i o n to be able to maximize forage u t i l i z a t i o n and p r o d u c t i v i t y . This n a t u r a l l y necessitates the accurate q u a n t i f i c a t i o n of the p a r t i c l e length d i s t r i b u t i o n i n processed forage; unfortunately, standard methods have not yet been developed. The research presented i n t h i s thesis was therefore undertaken to develop a method f o r quantifying the p a r t i c l e length d i s t r i b u t i o n of processed forage, and to determine the r e l a t i o n s h i p between the median p a r t i c l e length of a forage and the voluntary feed intake and chewing behavior of dairy c a t t l e . The research project consisted of f i v e experiments, the r e s u l t s of which are presented i n the following three chapters. Chapter 1 describes the development and t e s t i n g of a repeatable and accurate method f o r the analysis and d e s c r i p t i o n of the p a r t i c l e length d i s t r i b u t i o n i n chopped forage. Chapter 2 reports the r e s u l t s of an experiment to investigate the e f f e c t of processing method and forage species on the p a r t i c l e length and n u t r i e n t d i s t r i b u t i o n of chopped and hammermilled forage. The objective of t h i s part of the project was to determine i f , i n the preparation of dietary treatments of processed forage, d i f f e r e n t forages, processed by the same method, r e s u l t e d i n the production of s i m i l a r p a r t i c l e length and n u t r i e n t d i s t r i b u t i o n s . F i n a l l y , Chapter 3 reports the r e s u l t s of two experiments which investigated the r e l a t i o n s h i p between the median p a r t i c l e length of forage and the voluntary feed intake and chewing behavior of d a i r y c a t t l e . The development of equipment, and a method f o r the automatic monitoring of chewing a c t i v i t y are also described. -3- CHAPTER I DESCRIPTION OF THE PARTICLE LENGTH DISTRIBUTION OF CHOPPED FORAGE USING A SIMPLE VIBRATING TRAY FORAGE PARTICLE SEPARATOR AND A MODIFIED WEIBULL-TYPE FUNCTION INTRODUCTION The e f f e c t of p a r t i c l e s i z e reduction i n forages fed to ruminants on parameters of d i g e s t i o n including intake, d i g e s t i b i l i t y , chewing behavior, and rate of passage i s well documented. U n t i l recently, the i n v e s t i g a t i o n of the e f f e c t of forage p a r t i c l e s i z e on the process of d i g e s t i o n i n ruminants d i d not involve the quantitative analysis of the p a r t i c l e s i z e d i s t r i b u t i o n of the forage. T r a d i t i o n a l experimentation has examined the q u a l i t a t i v e d i f f e r e n c e between the e f f e c t s of feeding long, chopped and ground forages. To be able to quantitate the e f f e c t s of reducing the p a r t i c l e s i z e of forages i t i s necessary to have an objective method f o r the accurate measurement of p a r t i c l e s i z e . P a r t i c l e s i z e , however, with respect to forage p a r t i c l e s , can include a number of parameters such as length, width, breadth, diameter, cross s e c t i o n a l area, and volume. None of the e x i s t i n g methodology, f o r both the separation of p a r t i c l e s and the d e s c r i p t i o n of the r e s u l t i n g p a r t i c l e s i z e d i s t r i b u t i o n , appears to quantitate a s p e c i f i c s i z e parameter when applied to the separation of forage p a r t i c l e s . The s e l e c t i o n of the appropriate parameter or parameters to be q u a n t i f i e d should be based on t h e i r r e l a t i o n s h i p to b i o l o g i c a l function. Since i t appears that the maximum dimension of a p a r t i c l e may exert the greatest e f f e c t on forage u t i l i z a t i o n by l i m i t i n g the passage of p a r t i c l e s from the rumen, the development of a method f o r the q u a n t i t a t i o n of forage -4- p a r t i c l e l e n g t h , d e f i n e d as the maximum p a r t i c l e dimension, would be most app r o p r i a t e . Therefore, the present study was undertaken w i t h the f o l l o w i n g o b j e c t i v e s : 1) to design and c o n s t r u c t a v i b r a t i n g t r a y forage p a r t i c l e separator and t e s t i t s accuracy and p r e c i s i o n i n s e p a r a t i n g chopped forage p a r t i c l e s on the b a s i s of p a r t i c l e l e n g t h , 2 ) to mathematically define the d i s t r i b u t i o n of p a r t i c l e lengths i n chopped forage, 3) and to i d e n t i f y s t a t i s t i c a l parameters which would adequately de s c r i b e the p a r t i c l e l e n g t h d i s t r i b u t i o n s found i n chopped forages. -5- LITERATURE REVIEW MEASUREMENT OF FEEDSTUFF PARTICLE SIZE V i s u a l Separation A number of methods have been used to separate samples of concentrates and processed forages into component p a r t i c l e s i z e f r a c t i o n s . The simplest and most accurate method of p a r t i c l e s i z e analysis i s v i s u a l separation. I f p a r t i c l e s are s u f f i c i e n t l y large enough, a l l dimensions of the p a r t i c l e s can be measured using a r u l e r or a set of c a l i p e r s . Measurement of very small p a r t i c l e s , such as those i n feces or f i n e l y ground f e e d s t u f f s , may require the use of a microscope, u s u a l l y f i t t e d with cross-hairs and a graduated scale (Moseley, 1984). From the data that are c o l l e c t e d , the frequency d i s t r i b u t i o n of any measured p a r t i c l e s i z e parameter can be determined and then charac- t e r i z e d . Furthermore, during v i s u a l separation, measured pieces of f e e d s t u f f can be c o l l e c t e d i n small containers which can then be weighed to determine the weight d i s t r i b u t i o n of the p a r t i c l e sizes i n a given sample. A major disadvantage of v i s u a l separation, however, i s that i t i s very time consuming and tedious, and subject to large subsampling errors; a one kilogram sample of chopped forage may contain i n excess of 500,000 pieces which p r o h i b i t s the examination of a l l but the smallest subsamples (O'Dogherty, 1982). Therefore, the use of some form of automated method i s us u a l l y required. Sieving Both wet si e v i n g and dry si e v i n g techniques have been used to measure the p a r t i c l e s i z e d i s t r i b u t i o n of feeds t u f f s . Dry si e v i n g employs a stacked -6- s e r i e s of screens having d i f f e r e n t apertures which decrease i n s i z e from the top to the bottom of the stack. A representative sample i s placed on the top sieve and a g i t a t i o n of the sieve stack causes s o r t i n g of p a r t i c l e sizes by the l i m i t a t i o n of passage through each progressive screen i n r e l a t i o n to p a r t i c l e s i z e . Wet s i e v i n g i s s i m i l a r to dry s i e v i n g except that a stream or spray of solvent (usually water) i s added to wash the p a r t i c l e s through the stack of sieves. Standard s i e v i n g methods, developed p r i m a r i l y f or use i n the chemical and mineral r e l a t e d f i e l d s , have been adopted by the American Society of A g r i c u l t u r a l Engineers (ASAE) (American Society of A g r i c u l t u r a l Engineers, 1969a, 1983), the American Society of Animal Science (ASAS) (American Society of Animal Science, 1969) and the American Society of Dairy Science (Ensor et a l . . 1970) f o r the measurement of p a r t i c l e s i z e i n feedstuffs comprised of spheroidal or cuboidal shaped p a r t i c l e s as found i n concentrates. When si e v i n g spheroidal p a r t i c l e s , the range of p a r t i c l e sizes retained on a given sieve i s determined by the maximum diameter of the sieve aperture and the diameter of the sieve aperture d i r e c t l y above. Even though s i e v i n g has been described by the developers of s i e v i n g methodology f o r spheroidal p a r t i c l e s as being inappropriate f o r the " s i z i n g " of elongated p a r t i c l e s (American Society of A g r i c u l t u r a l Engineers, 1983), researchers have extensively used these techniques f o r p a r t i c l e s i z e measurement i n chopped and ground feedstu f f s , rumen samples, duodenal samples and f e c a l samples. The p a r t i c l e s i n these substances, however, have been shown to be predominantly elongated (Mosely, 1984; McLeod et a l . . 1984). The major problem with the si e v i n g of elongated p a r t i c l e s i s that the si z e parameter which controls the separation process has not been f u l l y elucidated. Uden and Van Soest (1982) found that a larger mean p a r t i c l e size -7- was obtained from wet s i e v i n g than was obtained by dry s i e v i n g . Since p a r t i c l e s are free to bounce around during dry s i e v i n g , the researchers concluded that dry s i e v i n g mainly measured diameter while wet s i e v i n g measured p a r t i c l e length. Jones and Mosely (1977) wet sieved rumen p a r t i c l e s c o l l e c t e d from sheep fed hay and clover d i e t s using wet s i e v i n g and then v i s u a l l y measured the actual length and width of p a r t i c l e s retained on each sieve. The lengths of p a r t i c l e s retained were about 3 to 4 times larger than the aperture of the sieve, while the width of the p a r t i c l e s were about 1/2 to 3/4 the s i z e of the sieve aperture. There was also a d i f f e r e n c e between the two forages i n the dimensions of the p a r t i c l e s that were retained on each sieve. The average length to width r a t i o of a l l the p a r t i c l e s was about f i v e to one. Since the p a r t i c l e sizes retained on each sieve v a r i e d with the s i z e of the sieve apertures that were being used and the f e e d s t u f f that was being separated, Moseley (1984) suggested that i t may be u s e f u l , by v i s u a l l y separating sieve f r a c t i o n s , to convert sieve f r a c t i o n s into p a r t i c l e length f r a c t i o n s . McLeod et a l . (1984) found that following wet s i e v i n g , the c o e f f i c i e n t of v a r i a t i o n for the p a r t i c l e length to aperture s i z e r a t i o s for p a r t i c l e s c o l l e c t e d on d i f f e r e n t sieves with d i f f e r e n t forages ranged from 20 to 41 percent, whereas that f o r the p a r t i c l e width to aperture s i z e r a t i o s ranged from 19 to 28 percent. Since the values and range of the c o e f f i c i e n t of v a r i a t i o n for the r a t i o of width to aperture s i z e were smaller, the researchers concluded that t h e i r wet s i e v i n g method was separating forage p a r t i c l e s predominantly on the basis of p a r t i c l e width, and not length. The width to aperture s i z e r a t i o s , however, were always less than one. Therefore, i t i s s t i l l unclear as to which s i z e parameter(s) i s being q u a n t i f i e d when elongated p a r t i c l e s are separated by s i e v i n g . -8- V i b r a t i n g Tray Separators V i b r a t i n g tray separators that are capable of measuring the p a r t i c l e length i n feedstuffs predominantly comprised of elongated p a r t i c l e s have been developed (Finner et a l . . 1978; Gale and O'Dogherty, 1982). The p r i n c i p l e of the separation of p a r t i c l e s on the basis of length by these machines assumes that the p a r t i c l e s e x h i b i t a length to width r a t i o greater than 1:1, are l o n g i t u d i n a l l y symmetrical, and e x h i b i t a constant length to weight r a t i o w i t h i n a p a r t i c l e . I f such a p a r t i c l e i s conveyed h o r i z o n t a l l y and l o n g i t u d i n a l l y over a gap, i n s t a b i l i t y occurs when the center of gravity of the p a r t i c l e reaches the edge of that gap. Further movement of the p a r t i c l e r e s u l t s i n overbalancing and the p a r t i c l e f a l l s through the gap. Therefore, elongated p a r t i c l e s passing over a gap of width X w i l l f a l l through the gap i f the length of the p a r t i c l e i s 2X or l e s s . I f p a r t i c l e s are conveyed over a cascading ser i e s of gaps, s t a r t i n g at the smallest gap and progressing to the largest, the p a r t i c l e s can be separated into length f r a c t i o n s . The t h e o r e t i c a l length of p a r t i c l e s c o l l e c t e d below a given gap w i l l range from the maximum length capable of f a l l i n g through the immediately preceding gap to twice the width of the designated gap. .Moller (1975) designed such a separator f o r measuring the length of forage p a r t i c l e s i n cobs and wafers. M o l l e r 1 s separator consisted of a sin g l e corrugated sheet of metal on which p a r t i c l e s were l o n g i t u d i n a l l y oriented and evenly dispersed. An eccentric, mounted on an e l e c t r i c motor, agit a t e d the corrugated sheet which was mounted on spring s t e e l straps. P a r t i c l e s were automatically applied to one end of the corrugated sheet and prop e l l e d over a se r i e s of holes of increasing diameter ( 1.4, 2, 4, 6, 8, and 10 mm.) which had been d r i l l e d at set i n t e r v a l s through the bottom of each channel i n the corrugated metal sheet. P a r t i c l e s longer than 20 mm i n -9- length were separated at the end of the tray by a ser i e s of three plates placed perpendicular to the bottom edge of the corrugated sheet to produce gaps of 15, 30 and 55 mm. Finner et a l . (1978) developed a separator which operated on the same p r i n c i p l e . The researchers, however, used a cascading s e r i e s of corrugated trays separated by progressively larger gaps. A l l the trays were i n c l i n e d at a 10 degree angle and were v i b r a t e d by an e l e c t r i c v i b r a t o r . Forage p a r t i c l e s were applied by hand to the top s o r t i n g tray and were propelled by gr a v i t y over each of the corrugated trays. Each successive tray was placed 0.5 times the gap width lower than the previous tray to enable a smoother passage of p a r t i c l e s and a more e f f i c i e n t overbalancing of the p a r t i c l e s . Gale and O'Dogherty (1982) designed a unique v i b r a t i n g tray separator which also used corrugated trays but the separation process operated i n reverse to those above with longer p a r t i c l e s being separated f i r s t , and pro g r e s s i v e l y shorter p a r t i c l e s being separated as they t r a v e l l e d down the serie s of trays. P a r t i c l e s were applied to the f i r s t tray by an asp i r a t o r column such that si n g l e pieces of forage were applied and oriented l o n g i t u d i n a l l y . A k n i f e edge placed at a given distance perpendicular to the f i r s t tray separated the longest p a r t i c l e s ; a l l p a r t i c l e s shorter than that required to pass over the gap passed through the gap on to the next tray. The next longest p a r t i c l e s were then removed i n a s i m i l a r manner with the shorter p a r t i c l e s passing to the next tray and so on. The separation of the longer p a r t i c l e s from the shorter p a r t i c l e s eliminated the clogging and other separation problems frequently encountered with the simple v i b r a t i n g tray separators described previously. -10- O s c i l l a t i n g Screen Separators A modified form of s i e v i n g uses o s c i l l a t i n g screen separators (Finner et a l . . 1978; F e l l e r and Foux, 1975). Unlike s i e v i n g which uses wire screens, o s c i l l a t i n g screen separators use large punched metal screens with larger apertures. These screens appear more sui t a b l e f o r separating chopped forages where greater numbers of the p a r t i c l e s exceed 2 to 3 cm. i n length. However, the r e l a t i o n s h i p between screen s i z e and p a r t i c l e s i z e and the s i z e parameter being measured using o s c i l l a t i n g screen separators, as with s i e v i n g , has not been elucidated. Finner et a l . (1978) bypassed t h i s problem by measuring the p a r t i c l e length of p a r t i c l e s retained on each screen d i r e c t l y using o p t i c a l imaging. O p t i c a l Imaging The newest form of p a r t i c l e s i z i n g involves o p t i c a l imaging. Finner et a l . (1978) described one system which used a Hewlett-Packard c a l c u l a t o r p l o t t e r system and the U n i v e r s i t y of Wisconsin Univac 1110 computer. P a r t i c l e s of forages were c a r e f u l l y spread over an X, Y g r i d on a h o r i z o n t a l glass screen such that no p a r t i c l e s were touching each other. P a r t i c l e endpoints were i d e n t i f i e d with the i n d i c a t o r arm of a d i g i t i z e r and the coordinates transmitted to the c a l c u l a t o r which determined and recorded the p a r t i c l e lengths. H a l l et a l . (1970) used the USDA F l y i n g Spot P a r t i c l e Analyzer (FSPA) to measure the cross s e c t i o n a l area of a l f a l f a stems. Measurements were made by photographing cross s e c t i o n a l views of stem sections on 35 mm f i l m and measuring the r e s u l t i n g image areas on the FSPA using a f l y i n g spot f i l m scanner. Luginbuhl et a l . (1984) photographed samples of p a r t i c l e s using a video camera and then d i g i t i z e d the image as a 256 x 256 array of points i n an Apple H e computer using an appropriate -11- i n t e r f a c e . Using the binary image, the perimeter, length and breadth of each p a r t i c l e could be measured and the projected surface area of the p a r t i c l e s c a l c u l a t e d . O p t i c a l imaging, once f u l l y developed, w i l l allow a more extensive analysis of p a r t i c l e s i z e which could be done more accurately and more r a p i d l y than using v i s u a l analysis. O p t i c a l imaging, however, s t i l l s uffers from l i m i t a t i o n s i n the s i z e of sample (usually l e s s than 1000 p a r t i c l e s ) that can be e f f i c i e n t l y analyzed, n e c e s s i t a t i n g e i t h e r the analysis of very large numbers of samples or the development of extremely accurate subsampling techniques. A further drawback to the use of o p t i c a l imaging i s that the weight d i s t r i b u t i o n of p a r t i c l e sizes i s not measurable. DESCRIPTION OF PARTICLE LENGTH DISTRIBUTIONS Frequency data The simplest method f o r describing the p a r t i c l e s i z e d i s t r i b u t i o n of a substance i s to report the percentage of p a r t i c l e s i n a sample having a given s i z e or range of s i z e s . Although the reporting of the complete sample p a r t i c l e length d i s t r i b u t i o n i n t h i s manner provides the most complete information regarding the p a r t i c l e s i z e d i s t r i b u t i o n , and has been recommended (Kennedy, 1984), i t does not lend i t s e l f e a s i l y to s t a t i s t i c a l t e s t i n g and communication between research groups. A complicating f a c t o r e x i s t s that not a l l researchers use the same p a r t i c l e s i z i n g methods, sieve s i z e s , or gaps on forage p a r t i c l e separators, to separate feedstuffs into component p a r t i c l e s i z e f r a c t i o n s . Furthermore, there i s l i t t l e evidence that the expression of p a r t i c l e s i z e i n t h i s manner aids i n the e l u c i d a t i o n -12- of the b i o l o g i c a l s i g n i f i c a n c e of s p e c i f i c p a r t i c l e s i z e parameters for ruminant f e e d s t u f f s . The quantitative d e s c r i p t i o n of the e f f e c t of p a r t i c l e s i z e on parameters of d i g e s t i o n i n ruminants necessitates the d e s c r i p t i o n of the whole p a r t i c l e s i z e d i s t r i b u t i o n by one or two parameters (namely a measure of c e n t r a l tendency and a measure of spread) which w i l l be independent of the method of separation used. Modulus of Fineness and Uniformity: One of the e a r l i e s t methods f o r the semi-quantitative d e s c r i p t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n of ground feedstuffs was the Modulus of Fineness, o r i g i n a l l y devised at the U n i v e r s i t y of Wisconson and l a t e r adopted by the ASAE as a recommended procedure (American Society of A g r i c u l t u r a l Engineers, 1969b). The procedure involves the dry s i e v i n g of a 250 gram sample of ground feed through a set of standard sieve sizes (3/8, 4, 8, 14, 28, 48, and 100 mesh plus the bottom pan) f o r 5 minutes with a ro-tap or other s i m i l a r method of shaking. The Modulus of Fineness i s c a l c u l a t e d by m u l t i p l y i n g the percent weight of the sample retained on each sieve by the sieve p o s i t i o n number ( s t a r t i n g with a value of 0.0 f o r the pan), summing the r e s u l t s and then d i v i d i n g by 100. An example of the c a l c u l a t i o n s , given by the ASAE (1969b) recommendation, i s i l l u s t r a t e d i n Table I. A major problem e x i s t s when using the Modulus of Fineness i n that two completely d i f f e r e n t d i s t r i b u t i o n s may have the same Modulus of Fineness depending upon how the material i s d i s t r i b u t e d throughout the sieve stack. For t h i s reason the Modulus of Uniformity was introduced as another recommendation of the ASAE as a descriptor of the spread of the p a r t i c l e s i z e d i s t r i b u t i o n (American Society of A g r i c u l t u r a l Engineers, 1969b). -13- TABLE I : ASAE (1969b) example c a l c u l a t i o n s f o r the d e t e r m i n a t i o n o f the Modulus o f F i n e n e s s o f ground f e e d s t u f f s by s i e v i n g . Screen Mesh Product of Percent of M a t e r i a l on Screen Times the Screen P o s i t i o n 3/8 1.0 x 2.5 x 7.0 x 24.0 x 35.5 x 22.5 x 7.5 x 0.0 x 7 6 5 4 3 2 1 0 7.0 15.0 35.0 96.0 4 8 14 28 48 100 Pan 106.5 45.0 7.5 0.0 T o t a l 100.0 312.0 Modulus of Fineness (312.0 / 100.0) =3.12 The uniformity of a sample i s expressed as the r a t i o of three numbers which represent the r e l a t i v e proportions of coarse, medium and f i n e p a r t i c l e s i n the sample. The sum of the figures always must equal 10 and the r a t i o s range from 10:0:0 to 0:0:10 gi v i n g 66 possible combinations. P a r t i c l e s c o l l e c t e d on the 3/8, 4 and 8 mesh sieves are designated as coarse, 14 and 28 mesh as medium and 48 and 100 mesh plus the pan as f i n e p a r t i c l e s . The Modulus of Uniformity i s determined by summing the percentage weight of p a r t i c l e s c o l l e c t e d on the sieves of a given s i z e category, d i v i d i n g the value by ten and rounding to a whole number. An example given by the ASAE (1969b) recommendation i s i l l u s t r a t e d i n Table I I . The Modulus of Fineness together with the Modulus of Uniformity adequately described the p a r t i c l e s i z e d i s t r i b u t i o n of ground feedstuffs i n a semi-quantitative manner for preliminary i n v e s t i g a t i o n of the e f f e c t s of fee d s t u f f p a r t i c l e s i z e on ruminant digestion. However, these methods are only applicable to the s i e v i n g of processed feedstuffs where the p a r t i c l e s i z e reduction process y i e l d s spheroidal or cuboidal shaped p a r t i c l e s . This -14- TABLE I I : ASAE (1969b) example c a l c u l a t i o n s for the determinat ion of the Modulus of Uni formity of ground feedstuf fs by s i e v i n g . Percent of Column (C) Screen Sample on Tota l s i n Column (B) Values Mesh Screen Div ided by 10 Rounded (A) (B) (C) (D) COARSE 3/8 1.0 4 2.5 8 7.0 10.5 / 10 = 1.05 1 MEDIUM 14 24.0 28 35.5 59.5 / 10 = 5.95 6 FINE 48 22.5 100 7.5 Pan 0.0 30.0 / 10 - 3.00 3 Modulus of Uni formity = 1:6:3 i s not the case with the process ing of forages . F u r t h e r m o r e , i f a d i f f e r e n t set of s ieves i s r equ ired to evenly d i s t r i b u t e the p a r t i c l e s throughout the s ieve s tack, the r e s u l t i n g Modulus of Fineness and Uni formi ty values are not comparable with those values obtained us ing the standard set of s i eves . A measure s i m i l a r to the Modulus of Fineness , known as Chop Modulus ( c i t e d by O'Dogherty, 1982), has been used to describe the p a r t i c l e length d i s t r i b u t i o n of chopped forage which had been separated in to four length f r a c t i o n s ( <25, 25-50, 50-100, and >100 mm) on a v i b r a t i n g tray separator . The percentage weight of the sample re ta ined i n each t ray was m u l t i p l i e d by a weight ing f a c t o r (1, 2, 4, or 8 r e s p e c t i v e l y ) . The r e s u l t i n g values were then summed and d i v i d e d by 100 to give the Chop Modulus. Unfortunate ly the Chop Modulus suf fers from the same l i m i t a t i o n as does the Modulus of Fineness i n that widely d i f f e r e n t p a r t i c l e length d i s t r i b u t i o n s can have the same Chop Modulus and that the method i s only semi -quant i ta t ive i n nature . -15- Mathematical D i s t r i b u t i o n Functions The i d e a l method for the d e s c r i p t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n of processed forage involves the i d e n t i f i c a t i o n of the underlying mathematical d i s t r i b u t i o n from which standard s t a t i s t i c a l parameters such as a mean, median and standard deviation (or other measure of spread) could be ca l c u l a t e d . The majority of the d i s t r i b u t i o n s of p a r t i c l e sizes i n processed feedstuffs are skewed to the r i g h t . As e a r l y as 1925, i t was demonstrated that the p a r t i c l e sizes of some comminuted substances could be described as being lognormally d i s t r i b u t e d (Murphy and Bohrer, 1984). However, i t was Kolomogoroff(1941) who f i r s t advanced a t h e o r e t i c a l explanation f o r the lognormal d i s t r i b u t i o n based on assumptions about comminution. The use of the lognormal d i s t r i b u t i o n , instead of the Modulus of Fineness and Modulus of Uniformity, f o r the d e s c r i p t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n i n ground feedstuffs (see Headley and Pfost, 1970) was f i r s t proposed by Headley and Pfost i n 1966 (Murphy and Bohrer, 1984). The procedure was l a t e r adopted by the ASAE as a recommended procedure (American Society of A g r i c u l t u r a l Engineers, 1969a) and s t i l l l a t e r as a standard procedure (American Society of A g r i c u l t u r a l Engineers, 1983) f o r the determination of the p a r t i c l e s i z e i n feedstuffs comprised of spheroidal or cuboidal p a r t i c l e s . However, the procedure i s not recommended to define the siz e of p a r t i c l e s which are flaked or elongated such as are found i n r o l l e d grains or chopped forage. The standard procedure involves the use of a standard set of sieve sizes s t a r t i n g with an aperture of 0.053 mm and each a d d i t i o n a l sieve getting p r o g r e s s i v e l y larger i n a geometric progression ( i e . the aperture of each a d d i t i o n a l seive i s "root 2" times the aperture of the previous sie v e ) . Sieving takes place on a s u i t a b l e sieve shaker and progresses u n t i l there i s -16- a constant d i s t r i b u t i o n of p a r t i c l e s between the sieves. Based on the assumption that the p a r t i c l e s sizes are lognormally d i s t r i b u t e d , the following equations can be used to determine the geometric mean diameter and the geometric standard deviation. d ^ = l o g " 1 ((ECWilogdi) / EWi)) S g w = l o g ' 1 ((EWiClogdi - l o g d g w ) 2 / ZW i ) 0 - 5 where: d g w = geometric mean diameter Sg W = geometric standard deviation d^ = aperture diameter of the i ' t h sieve d^ +^ = aperture diameter of the sieve placed j u s t above the i ' t h sieve d £ = g e o m e t r i c m e a n d i a m e t e r o f p a r t i c l e s o n t h e i ' t h s i e v e ( d ^ x d i + i ) ^ " ^ W£ = w e i g h t o f m a t e r i a l o n t h e i ' t h s i e v e Graphical methods can also be used to determine the geometric mean diameter and standard deviation, and to t e s t the goodness of f i t of the p a r t i c l e s i z e d i s t r i b u t i o n to the lognormal d i s t r i b u t i o n . I f a d i s t r i b u t i o n i s lognormally d i s t r i b u t e d , p l o t t i n g the cumulative percent weight of the sample retained on each sieve against the logarithm of the diameter of the aperture of that sieve on logarithmic p r o b a b i l i t y paper w i l l y i e l d a s t r a i g h t l i n e . A close f i t of the data points to a s t r a i g h t l i n e and a random d i s t r i b u t i o n of resi d u a l s around the l i n e i ndicates a good f i t of the data to the lognormal d i s t r i b u t i o n . I f the data adequately f i t s a s t r a i g h t l i n e , the geometric mean diameter can be read from the graph as the geometric diameter at the 50% p r o b a b i l i t y point and the geometric standard de v i a t i o n c a l c u l a t e d as the geometric diameter at the 84% p r o b a b i l i t y point -17- divided by the the geometric mean diameter. The geometric standard deviation can also be c a l c u l a t e d by d i v i d i n g the geometric mean diameter by the geometric diameter at the 16% p r o b a b i l i t y point. Another method of c a l c u l a t i n g the geometric mean diameter and standard deviation was presented by Waldo et a l . (1971). The d i s t r i b u t i o n of p a r t i c l e s i z e s was expressed as the cumulative percent of p a r t i c l e s by weight passing through a sieve aperture of s i z e X ( i n microns). The percent weight of the sample capable passing through each sieve was transformed to normal equivalent deviates (Y) and regressed on the base ten logarit h i m of the sieve aperture s i z e (X) using the equation Y = a + blog^g x- l n standardized normal form Y = (logX - logu) / logS = (-logu / logS) + 1/logS x logX where logu i s the geometric mean diameter and logS i s the geometric standard deviation. The geometric mean diameter could therefore be estimated by -a/b and the geometric standard deviation by 1/b. The b e n e f i t of using the lognormal d i s t r i b u t i o n i s that the p a r t i c l e s i z e d i s t r i b u t i o n can be described completely by two parameters, the geometric mean diameter and the geometric standard deviation. Furthermore, once the geometric mean diameter and standard deviations by weight are known, the d i s t r i b u t i o n s of p a r t i c l e numbers and surface area of spheroidal and cuboidal shaped p a r t i c l e s can also be described, and a l l three d i s t r i b u t i o n s w i l l have the same geometric standard d e v i a t i o n (Headley and Pfost, 1970). Whereas the lognormal d i s t r i b u t i o n methods described above are only appl i c a b l e f o r the d e s c r i p t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n of sieved spheroidal and cuboidal p a r t i c l e s , s i m i l a r procedures can be used i f -18- p a r t i c l e length i s measured on a v i b r a t i n g tray separator (0'Dogherty,1984). Where applicable i n each a n a l y t i c a l procedure above, the sieve diameter i s replaced by the minimum or maximum t h e o r e t i c a l p a r t i c l e length capable of f a l l i n g through each gap on the separator. The r e s u l t s of the c a l c u l a t i o n s w i l l then y i e l d the geometric mean p a r t i c l e length and standard deviation. Any subsequent c a l c u l a t i o n s of the d i s t r i b u t i o n of p a r t i c l e numbers and surface area are, however, no longer v a l i d . Other d i s t r i b u t i o n s which have been f i t t e d to p a r t i c l e s i z e data obtained from the s i e v i n g of feedstuffs include the Gamma p r o b a b i l i t y density function and the Rosin-Rammler or Weibull function. These are exponential functions which e x h i b i t great f l e x i b i l i t y when f i t t e d to p r o b a b i l i t y density functions or sigmoidal shaped cumulative frequency d i s t r i b u t i o n s of p a r t i c l e sizes such as are found i n processed feedstuffs and other substances. Exponential d i s t r i b u t i o n s such as the Weibull function are f i t t e d to the data using non-linear regression of the percent cumulative weight undersize on sieve s i z e , or p a r t i c l e length as determined by v i b r a t i n g tray separators. The median p a r t i c l e s i z e or p a r t i c l e length of the d i s t r i b u t i o n i s c a l c u l a t e d by solv i n g the regression equation f o r the cumulative percent undersize equal to 50%. Unfortunately, computational procedures have not been put forward f o r a measure of the spread of the d i s t r i b u t i o n . The Gamma p r o b a b i l t i t y density function, though hi g h l y f l e x i b l e , involves a recursive gamma function which makes the parameterizing process computationally formidable (Yang et a l . . 1978). A l l e n et a l . (1984), however, f i t the Gamma p r o b a b i l i t y density function using a procedure i n v o l v i n g maximum l i k l i h o o d estimators f o r the parameters i n the function. Herdan (1960) recommended the use of the Rosin-Rammler (or Weibull) -19- function when the d i s t r i b u t i o n of p a r t i c l e sizes deviated from normality to the point that the lognormal d i s t r i b u t i o n could not be adequately f i t t e d to separation data. Furthermore, Rose (1954) demonstrated that for an exponential d i s t r i b u t i o n , the d i s t r i b u t i o n of p a r t i c l e sizes on a number or weight basis was independent of the sample s i z e and the shape or density of the p a r t i c l e s being separated. Therefore, the use of an exponential d i s t r i b u t i o n to describe the weight d i s t r i b u t i o n of processed feedst u f f p a r t i c l e s by s i e v i n g does not require any assumptions regarding p a r t i c l e geometry or density as i t does when the lognormal d i s t r i b u t i o n i s used (Pond et a l . . 1984). Since the s i z e parameter that i s measured by the s i e v i n g of elongated p a r t i c l e has not yet been elucidated, none of the procedures described above i s v a l i d f o r the measurement of p a r t i c l e s i z e of elongated p a r t i c l e s by s i e v i n g . However, researchers have used these procedures for the d e s c r i p t i o n of p a r t i c l e s i z e i n processed forages, boluses c o l l e c t e d through esophageal f i s t u l a s , rumen contents, duodenal digesta, and f e c a l samples, a l l of which are predominantly comprised of elongated p a r t i c l e s . The procedures do have some v a l i d i t y i f the measurement of a s i z e parameter i s not implied and the r e s u l t s are simply expressed as the percentage of p a r t i c l e s capable of passing a given s i z e of sieve aperture (Kennedy, 1984). The goodness of f i t of the lognormal d i s t r i b u t i o n to the r e s u l t s of the s i e v i n g of feedstuffs comprised of elongated p a r t i c l e s has been v a r i a b l e . Waldo et a l . (1971) found that the assumption of lognormality f o r the d i s t r i b u t i o n of p a r t i c l e sizes i n f e c a l samples was adequate, but that the d i s t r i b u t i o n of p a r t i c l e sizes i n chopped and p e l l e t e d orchardgrass hay s i g n i f i c a n t l y d i f f e r e d from lognormal. The researchers concluded, however, that the f i t was adequate for many p r a c t i c a l and s c i e n t i f i c purposes. A l l e n -20- et a l . (1984) also found a s i g n i f i c a n t lack of f i t of separation data to the lognormal d i s t r i b u t i o n when the p a r t i c l e s i z e d i s t r i b u t i o n of ground forages and f e c a l samples was examined by the procedure of Waldo et a l . (1971). A b e t t e r f i t was obtained when the lognormal p r o b a b i l i t y density function was f i t t e d to the data by maximum l i k e l i h o o d estimators of the log mean and standard deviation: t h i s i s s i m i l a r to the method of c a l c u l a t i n g the geometric mean diameter and standard deviation described above using the weights of p a r t i c l e s retained on each sieve. The best o v e r a l l f i t t i n g of the data, however, was obtained using the Gamma p r o b a b i l i t y density function. Pond et a l . (1984) sieved samples of grazed coa s t a l Bermuda grass taken from the esophagus, upper and lower rumen s t r a t a , and feces of c a t t l e , and then f i t the p a r t i c l e d i s t r i b u t i o n data to the lognormal d i s t r i b u t i o n and an exponential d i s t r i b u t i o n based on a modified Rosin-Rammler or Weibull function. The researchers concluded that the use of the lognormal d i s t r i b u t i o n was inappropriate for describing the p a r t i c l e s i z e d i s t r i b u t i o n of a l l the samples because the f i t t e d curves exhibited s i g n i f i c a n t k u r t o s i s and skewness. They also concluded that the exponential d i s t r i b u t i o n more c l o s e l y f i t the observed data and that i t s use was therefore more appropriate i n describing the p a r t i c l e s i z e d i s t r i b u t i o n i n samples comprised of elongated p a r t i c l e s . Smith et a l . (1984) found that when the c e l l wall p a r t i c l e s i z e d i s t r i b u t i o n of digesta samples (procedure of Smith and Waldo, 1969) from a l f a l f a , orchardgrass and corn s i l a g e fed c a t t l e was determined by sieving, the exponential d i s t r i b u t i o n used by Pond et a l . (1983, 1984) o f f e r e d no advantages, and d i d not improve the f i t of the data, as compared to the lognormal d i s t r i b u t i o n . The e x t r a c t i o n of the samples with a n eutral detergent s o l u t i o n p r i o r to s i e v i n g may, however, have a l t e r e d the p a r t i c l e -21- s i z e d i s t r i b u t i o n s of the samples. Furthermore, the researchers based t h e i r comparison of the goodness of f i t between the lognormal and Weibull d i s t r i b u t i o n s on the comparison of the c o e f f i c i e n t s of determination, d i s t r i b u t i o n of r e s i d u a l s , and r e s i d u a l sums of squares f o r two d i s s i m i l a r regression equations. The lognormal regression was performed by l i n e a r regression of p r o b i t transformed cumulative percent weight undersize on the logarithm of sieve s i z e , while the f i t t i n g of the Weibull function was performed by nonlinear regression of the cumulative percent weight undersize on sieve s i z e . Murphy and Bohrer (1984) examined some tenable assumptions regarding the comminution of elongated p a r t i c l e s which could lead to the lognormal or Rosin-Rammler p a r t i c l e s i z e d i s t r i b u t i o n s . The researchers' assumptiions did not lead to the generation of a lognormal d i s t r i b u t i o n . However, even though they admitted that the Rossin-Rammler d i s t r i b u t i o n would f i t the r e s u l t s better, Murphy and Bohrer (1984) concluded that r e s o l v i n g the lognormal d i s t r i b u t i o n of i t s components would provide more information than would "glossing" over the differences between the data and the lognormal d i s t r i b u t i o n with the use of another d i s t r i b u t i o n such as the Rosin-Rammler. One could argue that the use of any parameters derived from a mathematical d i s t r i b u t i o n that d i d not c o r r e c t l y f i t the observed data could introduce err o r into experimental r e s u l t s that r e l y on the accurate q u a n t i f i c a t i o n of p a r t i c l e s i z e . L i t t l e information i s a v a i l a b l e regarding the mathematical d e f i n i t i o n of the d i s t r i b u t i o n of p a r t i c l e lengths i n processed f e e d s t u f f s . Gale and O'Dogherty (1982) found that the p a r t i c l e length d i s t r i b u t i o n of chopped forage separated on a v i b r a t i n g tray separator could be approximated by a lognormal d i s t r i b u t i o n , but showed no s t a t i s t i c a l t e s t i n g to prove the -22- point. The graphical representation of an observed p a r t i c l e length d i s t r i b u t i o n , however, exhibited a s i n u s o i d a l d i s t r i b u t i o n of resi d u a l s around the regression l i n e . Such a d i s t r i b u t i o n of resi d u a l s would indicate a lack of f i t . O'Dogherty (1984) found that some observed p a r t i c l e length d i s t r i b u t i o n s diverged from lognormality i n the " t a i l s " of the d i s t r i b u t i o n , but concluded that the d i s t r i b u t i o n s were, i n general, an adequate approximation of a lognormal d i s t r i b u t i o n over much of the p a r t i c l e length range. No other examples of the f i t t i n g of p a r t i c l e length d i s t r i b u t i o n s , determined using v i b r a t i n g tray separators, to known d i s t r i b u t i o n s are a v a i l a b l e . MATERIALS AND METHODS SEPARATION OF FORAGE PARTICLES A v i b r a t i n g tray Forage P a r t i c l e Separator (FPS) was developed to enable the separation of chopped forage p a r t i c l e s on the basis of length (see Figure 1); i t s design was based on the v i b r a t i n g tray separator developed by Finner et a l . (1978) . The FPS was comprised of a tray bed, bed frame and base frame. The tray bed was comprised of a cascading ser i e s of seven corrugated trays made from enamel coated sheet s t e e l mounted on a tray frame made from 50.4 cm angle i r o n . The f i r s t tray, f o r the a p p l i c a t i o n and alignment of p a r t i c l e s , was 61 cm long followed by one 25 cm and then f i v e 20 cm long separation trays, each measuring 76 cm i n width. The trays were separated by gaps measuring 2, 2, 5, 10, 20, and 40 mm r e s p e c t i v e l y and each successive tray was positioned one h a l f the gap size lower than the preceeding tray. Two 2 mm gaps were used because the smallest length f r a c t i o n comprised a large part of the forage samples and was the most d i f f i c u l t to separate. The corrugated trays were strengthened and aligned by wood and metal supports which were attached to the tray frame by 15 cm long pieces of 12.7 mm threaded rod. S l o t t e d holes i n the tray frame and the use of threaded rod permitted unlimited adjustment of the trays. The tray bed (trays plus tray frame) was bolted at a 13 degree angle to the bed frame. The bed frame i n turn was bolted to the four c a n t i l e v e r supports of the base frame. The bed frame and base frame were both constructed from 7.62 cm channel i r o n . A 2.54 cm pneumatic p i s t o n v i b r a t o r was mounted to the front of the bed frame. The frequency and amplitude of the v i b r a t i o n was adjusted by an a i r pressure -24-  regulator mounted on the base frame. The design of the separator was such that when the correc t v i b r a t i o n frequency was applied to the bed frame, i t would v i b r a t e h o r i z o n t a l l y at the natural harmonic frequency of the c a n t i l e v e r supports. This v i b r a t i o n was transmitted evenly to the separator trays by the mounting of the tray bed to the bed frame and caused the forage p a r t i c l e s to "flow" down the grooves i n the trays without bouncing or jumping the gaps between trays. During separation the forage p a r t i c l e s were applied by hand to the top a p p l i c a t i o n and alignment tray such that there was no clumping of p a r t i c l e s . P a r t i c l e s f a l l i n g through each gap were c o l l e c t e d below i n mounted p l e x i g l a s s c o l l e c t i o n trays. The arrangement of separation trays that was used t h e o r e t i c a l l y r e s u l t e d i n the separation of the following s i x p a r t i c l e length f r a c t i o n s according to the "overbalancing p r i n c i p l e " : <4, 4-10, 10-20, 20-40, 40-80, and >80 mm. Once a sample had been separated, the p a r t i c l e s c o l l e c t e d i n each of the c o l l e c t i o n trays were tr a n s f e r r e d into tared p l a s t i c bags and weighed. The r e s u l t s of the separation were expressed as the percent of sample weight, on an a i r dry basis, that was c o l l e c t e d i n each of the t h e o r e t i c a l p a r t i c l e length f r a c t i o n s . FORAGE PARTICLE SEPARATOR TESTING FPS Separation of Hand Chopped A l f a l f a Hay A sample of baled a l f a l f a hay was chopped by hand on a paper cutter such that a wide d i s t r i b u t i o n of p a r t i c l e lengths was produced. The chopped a l f a l f a was then subdivided into four samples which comprised the t o t a l amount of a l f a l f a chopped. Each subsample was separated on the FPS into -26- p a r t i c l e l e n g t h f r a c t i o n s w h i c h w e r e t h e n w e i g h e d . T o t e s t t h e e f f e c t o f m e t h o d o f s e p a r a t i o n o n t h e r e p r o d u c i b i l i t y o f F P S r e s u l t s , t h e p a r t i c l e l e n g t h f r a c t i o n s c o l l e c t e d f r o m t h e s e p a r a t i o n o f a g i v e n s u b s a m p l e w e r e t h e n r e s e p a r a t e d c o n s e c u t i v e l y , s t a r t i n g w i t h t h e s h o r t e s t l e n g t h f r a c t i o n a n d e n d i n g w i t h t h e l o n g e s t . T h e p a r t i c l e l e n g t h f r a c t i o n s r e s u l t i n g f r o m r e s e p a r a t i o n w e r e t h e n w e i g h e d . T h i s r e s e p a r a t i o n w a s p e r f o r m e d a s e c o n d t i m e r e s u l t i n g i n t h r e e s e p a r a t i o n s o f e a c h s u b s a m p l e . T h e e f f e c t o f t h e m e t h o d o f s e p a r a t i o n o n t h e p e r c e n t o f s u b s a m p l e w e i g h t c o l l e c t e d i n e a c h p a r t i c l e l e n g t h f r a c t i o n w a s t e s t e d b y t h e f o l l o w i n g G e n e r a l L i n e a r H y p o t h e s i s u s i n g t h e B M D : 1 0 V p a c k a g e p r o g r a m o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a : Y i j k = u + F i + R i j + s i k + E i j k w h e r e : Y ^ j ^ = t h e d e p e n d e n t v a r i a b l e : p e r c e n t o f s u b s a m p l e w e i g h t c o l l e c t e d . u = t h e o v e r a l l m e a n . F i = t h e e f f e c t o f t h e i ' t h g a p i n t h e F P S ( i e . p a r t i c l e l e n g t h f r a c t i o n ) . R ^ j = t h e e f f e c t o f t h e j ' t h s e p a r a t i o n r u n n e s t e d w i t h i n t h e i ' t h f r a c t i o n . S ^ = ^ e e f f e c t o f t h e k ' t h s u b s a m p l e n e s t e d w i t h i n t h e i ' t h f r a c t i o n . E i j ^ = t h e r e s i d u a l e r r o r a s s o c i a t e d w i t h t h e i n t e r a c t i o n b e t w e e n t h e j ' t h s e p a r a t i o n r u n a n d t h e k 1 t h s u b s a m p l e w i t h i n t h e i ' t h f r a c t i o n . D i f f e r e n c e s i n t h e p e r c e n t w e i g h t o f s a m p l e c o l l e c t e d i n e a c h p a r t i c l e l e n g t h f r a c t i o n , b e t w e e n s a m p l e s a n d s e p a r a t i o n r u n s w i t h i n p a r t i c l e l e n g t h f r a c t i o n s , w e r e t e s t e d u s i n g D u n c a n ' s M u l t i p l e R a n g e t e s t ( a = 0 . 0 5 ) . -27- FPS vs. V i s u a l Separation of Machine Chopped Orchardgrass Hay Three bales of mature orchardgrass hay were broken open and the bale sheaves randomly a l l o c a t e d into three p i l e s . Each p i l e of sheaves, selected at random was then chopped at one of three t h e o r e t i c a l lengths of cut (TLC = 3.18, 6.35, or 9.54 mm) on a John Deere Model 35 Forage Harvester f i t t e d with 6 Blades. The TLC was changed by a l t e r i n g the infeed gear r a t i o s according to machine s p e c i f i c a t i o n s . The chopped hay was blown into an array of four groups of three subsampling boxes arranged as shown i n Figure 2. One box from each of the groups was randomly a l l o c a t e d to one of three samples. The chopped forage contained i n s i m i l a r l y numbered subsample boxes was composited and then subsampled by quartering into a 50g sample (approx 1.0 l i t r e volume) before being separated on the FPS. A f t e r the p a r t i c l e length f r a c t i o n s of each sample were weighed, s i m i l a r length f r a c t i o n s w i t h i n each sample of a given TLC were composited and then divided into two subsamples. These subsamples were v i s u a l l y separated to determine the actual p a r t i c l e length d i s t r i b u t i o n f o r each p a r t i c l e length f r a c t i o n w i t h i n a given TLC. The p a r t i c l e s were measured with a r u l e r and separated manually into as many as 26 length f r a c t i o n s which were then weighed. The f i r s t two f r a c t i o n s contained p a r t i c l e s that ranged i n length from 0-4 and 4-10 mm r e s p e c t i v e l y . P a r t i c l e s ranging from 10 to 80 mm were separated i n 5 mm increments. The remaining longer p a r t i c l e s were separated i n 10 mm increments. The actual p a r t i c l e length d i s t r i b u t i o n f o r each p a r t i c l e length f r a c t i o n c o l l e c t e d on the FPS was c a l c u l a t e d by m u l t i p l y i n g the v i s u a l l y determined percent weight of a given range of p a r t i c l e lengths i n the f r a c t i o n by the weight of a l l the p a r t i c l e s c o l l e c t e d i n that f r a c t i o n on the FPS. The actual p a r t i c l e length d i s t r i b u t i o n f o r each TLC was then -28- FIGURE 2: Arrangement of 4 groups of subsampling boxes f o r obtaining 3 representative samples of a chopped forage. -29- determined by summing the v i s u a l l y determined p a r t i c l e length d i s t r i b u t i o n s of the p a r t i c l e length f r a c t i o n s that were c o l l e c t e d from the samples of a given TLC. This method of v i s u a l separation r e s u l t e d i n the determination of a s i n g l e actual p a r t i c l e length d i s t r i b u t i o n f or each set of TLC samples separated on the FPS. Both the v i s u a l l y and FPS determined p a r t i c l e length d i s t r i b u t i o n s were expressed as the percent of a i r dry sample weight comprising a given range of p a r t i c l e lengths. The v i s u a l separation data were also used to c a l c u l a t e the percentage weight of p a r t i c l e s i n each TLC sample, and i n each length f r a c t i o n of the sample c o l l e c t e d on the FPS, that was c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d on the basis of length by the FPS. The p a r t i c l e length d i s t r i b u t i o n s determined using the FPS were compared with those determined v i s u a l l y by the Chi squared goodness of f i t t e s t (Choi, 1978) using the v i s u a l data as the expected p a r t i c l e length d i s t r i b u t i o n . The consistency of FPS p a r t i c l e s i z i n g accuracy of d i f f e r e n t lengths of p a r t i c l e s and of p a r t i c l e s i n each p a r t i c l e length f r a c t i o n c o l l e c t e d on the FPS was tested using a Chi squared contingency table (Choi, 1978) . Differences i n the degree of undersizing and o v e r s i z i n g error by the FPS between p a r t i c l e length f r a c t i o n s and between TLC, f o r a l l p a r t i c l e lengths as a whole, were tested by the Chi squared comparison of several proportions t e s t (Choi, 1978). The diffe r e n c e between the degree of o v e r s i z i n g and undersizing by the FPS was then used to c a l i b r a t e the t h e o r e t i c a l p a r t i c l e length f r a c t i o n s that were being c o l l e c t e d on the FPS. DESCRIPTION OF PARTICLE LENGTH DISTRIBUTIONS The v i s u a l and FPS separation data f o r chopped mature orchardgrass hay described above were converted to the percent cumulative weight of sample -30- p a r t i c l e s that were shorter than the maximum length t h e o r e t i c a l l y capable of passing through each gap on the FPS ( i e . Percent Cumulative Weight Undersize). For a l l but the l a s t c o l l e c t i o n tray, the maximum length of p a r t i c l e capable of passing through a given gap was determined from the c a l i b r a t i o n of the FPS above. The maximum p a r t i c l e length c o l l e c t e d i n the l a s t c o l l e c t i o n tray was determined by measuring the longest p a r t i c l e i n the that tray. The cumulative percent weight of p a r t i c l e s undersize (Y) was then regressed on p a r t i c l e length (X) using each of the following mathematical equations: 1: Y = a + bX 2: Y = a + blogX 3: logY = a + blogX 4: Y = a + blogX (Y i n standard p r o b a b i l i t y u n i t s - Waldo et a l . . 1971) C -(BX) 5: Y = 100 x (1 - e ) (Modified Weibull or Rossin-Rammler type function- Yang et a l . . 1978) Equations 1, 2, 3, and 4 were f i t t e d to the data by l i n e a r regression using the BMD:P1R packaged program of the U n i v e r s i t y of B r i t i s h Columbia. The Weibull function (equation 5) was f i t t e d to the data by non-linear regression using the BMD:PAR packaged program of the U n i v e r s i t y of B r i t i s h Columbia. The c o e f f i c i e n t s of determination and d i s t r i b u t i o n of residuals f o r each regression l i n e were compared to determine goodness of f i t of each data set to the l i n e s predicted by each regression equation. Regression equations 2, 4 and 5 were used to p r e d i c t the percent weight of sample p a r t i c l e s that were c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on -31- the FPS. To compare the goodness of f i t between the regression equations, the predicted p a r t i c l e length d i s t r i b u t i o n from each regression equation was compared with the observed p a r t i c l e length d i s t r i b u t i o n using the Chi squared goodness of f i t t e s t ( A l l e n et a l , 1984). The median p a r t i c l e lengths (the length of 50% Cumulative Weight Undersize) f o r v i s u a l and separation data were predicted using regression equations 2, 4 and 5. The predicted median p a r t i c l e lengths were su b j e c t i v e l y compared f o r accuracy and consistency between regression equations, TLC samples, and method of separation; lack of r e p l i c a t i o n of v i s u a l separation data d i d not permit s t a t i s t i c a l t e s t i n g of any differences i n the predicted median p a r t i c l e lengths. -32- RESULTS AND DISCUSSION OPERATION OF THE FORAGE PARTICLE SEPARATOR The ease of separation of chopped forage p a r t i c l e s on the FPS ranged from e f f o r t l e s s to very d i f f i c u l t . Similar separation problems to those described by Finner et a l . (1978) and Gale and O'Dogherty (1982) were encountered. I d e a l l y shaped p a r t i c l e s resembling uniform rods separated e f f o r t l e s s l y as theorized. Chopped forage samples, however, contain a v a r i a b l e proportion of i r r e g u l a r l y shaped p a r t i c l e s . "U" shaped p a r t i c l e s and p a r t i c l e s that lack s t r u c t u r a l r i g i d i t y could thread t h e i r way through gaps that were smaller than those which they should t h e o r e t i c a l l y have been able to f a l l through. "L" shaped p a r t i c l e s and p a r t i c l e s with rough edges could get snagged i n gaps as they passed down the separator. This snagging would dramatically increase the time required to separate a sample by causing the gaps to become clogged which, i n turn, caused appropriately s i z e d p a r t i c l e s to flow over the gap that they otherwise would have f a l l e n through. Because of these separation problems, constant s u r v e i l l a n c e was necessary to unclog gaps between trays. Most trapped p a r t i c l e s were pushed through the gap they were clogging with the exception of obviously long p a r t i c l e s which were saved and reoriented to continue down the separator. These major separation problems were s u c c e s s f u l l y avoided i n the machine designed by Gale & O'Dogherty (1982). However, the construction cost and complexity of design of that separator precluded a s i m i l a r design i n t h i s study. Because the a l f a l f a hay contained more i r r e g u l a r i l y shaped p a r t i c l e s , i t was c o n s i s t e n t l y more d i f f i c u l t to separate than was the orchardgrass hay. With both forages, shorter p a r t i c l e s tended to separate more e a s i l y than did longer p a r t i c l e s because these p a r t i c l e s tended to be more i d e a l l y shaped and more r i g i d . Therefore, orchardgrass hay chopped at the short TLC was easier to separate than that chopped at the long TLC. Separation times for a l l samples ranged from 15 minutes to 2 hours with the average time for separation being about 30 minutes. FORAGE PARTICLE SEPARATOR TESTING FPS Separation of Hand Chopped A l f a l f a Hay The r e s u l t s of the separation of hand chopped a l f a l f a hay are shown i n Table I I I . The subsample being separated had a s i g n i f i c a n t e f f e c t (P < 0.05) on the proportion of sample weight c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on the FPS. This e f f e c t , however, was consistent over the three TABLE I I I : Average percent of sample weight (n = 4) of hand chopped a l f a l f a hay c o l l e c t e d i n each p a r t i c l e length f r a c t i o n a f t e r each of three separation runs on the Forage P a r t i c l e Separator. THEORETICAL RANGE OF PARTICLE LENGTHS (mm) <4 4 -10 10- 20 20 -40 40- 80 >80 1 10. l a 15 .4 a 34. 7 b 23 .0 b 13. 7 3.2 RUN* 2 11. 7 b 16 .7 b 33. 7 a 21 .0 a 13. 8 3.2 3 12. 2 b 17 .2 b 33. l a 20 .6 a 13. 7 3.3 Means with i n each p a r t i c l e length f r a c t i o n having d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). Run 1; each sample was separated as a whole sample. Runs 2 & 3; the p a r t i c l e length d i s t r i b u t i o n f o r each sample was determined by consecutively separating the p a r t i c l e length f r a c t i o n s c o l l e c t e d i n the previous run. -34- runs. Since each subsample should have had a s i m i l a r p a r t i c l e length d i s t r i b u t i o n t h i s e f f e c t must have been caused by subsampling error. The method of separation also had a s i g n i f i c a n t e f f e c t on the proportion of sample weight c o l l e c t e d i n each length f r a c t i o n . There was a s i g n i f i c a n t increase (P < 0.05) i n the amount of p a r t i c l e s i n the shorter p a r t i c l e length f r a c t i o n s (<4, 4-10 mm) and a decrease i n the 10-20 and 20-40 mm f r a c t i o n s when the samples were reseparated from the p a r t i c l e length f r a c t i o n s c o l l e c t e d i n the f i r s t run; the 40-80mm and >80mm f r a c t i o n weights did not change s i g n i f i c a n t l y (P > 0.05). There was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05), however, between the second and t h i r d runs i n the p a r t i c l e length d i s t r i b u t i o n of the samples when they were reseparated from the p a r t i c l e length f r a c t i o n s c o l l e c t e d i n the second run. Finner et a l . (1978) separated each sample of a chopped forage, as a whole, three times on t h e i r simple v i b r a t i n g separator and found that the standard deviation for the percent sample weight c o l l e c t e d through each gap among the three runs was only about one percent; the average c o e f f i c i e n t of v a r i a t i o n was about three percent. Therefore, i t appears that the r e s u l t s of separating chopped forage on a simple v i b r a t i n g separator are very reproducible as long as a sing l e method of a p p l i c a t i o n of forage p a r t i c l e s to the separator i s used. The movement of p a r t i c l e s from the middle length f r a c t i o n s to smaller length f r a c t i o n s between runs 1 and 2 indicated that there could have been an i n t e r a c t i o n between the two length groups which caused shorter p a r t i c l e s to pass over the correct gaps when the sample was separated as a whole. On the other hand, since the greatest proportion of sample p a r t i c l e s was of medium length, separation of these f r a c t i o n s as a u n i t may have increased the opportunity f o r these p a r t i c l e s to pass through the smaller gaps. This question of p a r t i c l e s i z i n g accuracy was investigated i n a separate experiment. FPS vs. V i s u a l Separation of Machine Chopped Orchardgrass Hay Af t e r the machine chopped orchardgrass hay had been separated on the FPS, the r e s u l t i n g p a r t i c l e length f r a c t i o n s were separated v i s u a l l y to determine the accuracy of the FPS i n separating chopped forage p a r t i c l e s on the basis of length. A mature grass hay was used because i t contained a high proportion of i d e a l l y shaped p a r t i c l e s when chopped. There was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) between the p a r t i c l e length d i s t r i b u t i o n s determined using the FPS and those determined v i s u a l l y (Table IV). There was, however, a consistent trend with a l l TLC towards an underestimation of the weight of p a r t i c l e s i n the 4-10 mm f r a c t i o n and an overestimation of the weight of p a r t i c l e s i n the 20-40, 40-80 and >80 mm f r a c t i o n s when the p a r t i c l e length d i s t r i b u t i o n s were determined using the FPS. The proportion of material, comprising each t h e o r e t i c a l p a r t i c l e length TABLE IV: P a r t i c l e length d i s t r i b u t i o n s (percent of sample weight) of mature orchardgrass hay, chopped at three t h e o r e t i c a l lengths of cut (TLC), determined by the FPS and by v i s u a l (VIS) separation. THEORETICAL RANGE OF PARTICLE LENGTHS (mm) TLC (mm) <4 4-10 10-: 20 20-. 40 40- 80 >80 CHI 2 3.18 FPS 15. 9 18.7 30 .3 22 .8 10 .5 2. .0 5.350 VIS 18. 1 25.9 27 .1 20 .8 7 .1 1, .0 6.35 FPS 10. 8 15.5 35 .1 23 .5 12 .8 2. .5 10.625 VIS 8. 4 29.7 30 .1 21 .3 8 .8 1. .7 9.53 FPS 7. 5 9.7 37 .6 29 .2 13 .9 2, .1 7.647 VIS 6. 2 18.4 39 .6 22 .5 10 .9 1. .3 mean FPS 10. 9 14.1 34 .7 25 .6 12 .6 2 .2 6.254 VIS 10. 4 24.0 33 .0 21 .6 9 .6 1 .3 -36- f r a c t i o n c o l l e c t e d on the FPS, that was c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d by length i s given i n Table V. The d i s t r i b u t i o n of c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d p a r t i c l e s i n each p a r t i c l e length f r a c t i o n was not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) between TLC samples. There was, however, a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) between p a r t i c l e length f r a c t i o n s i n the percent weight of p a r t i c l e s that was c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d . The 4-10 mm f r a c t i o n contained the greatest proportion of c o r r e c t l y c l a s s i f i e d p a r t i c l e s (65.9%) which was s i g n i f i c a n t l y higher (P < 0.05) than the proportion c o r r e c t l y c l a s s i f i e d i n the 20-40 mm and the >80 mm f r a c t i o n s , not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) from the proportion c o r r e c t l y c l a s s i f i e d i n the remaining f r a c t i o n s . The >80 mm f r a c t i o n contained the lowest proportion of c o r r e c t l y c l a s s i f i e d p a r t i c l e s (39.6%) which was s i g n i f i c a n t l y l e s s (P < 0.05) than the proportion c o r r e c t l y c l a s s i f i e d i n the other f r a c t i o n s , with the exception of the 20-40 mm f r a c t i o n . The proportion of p a r t i c l e s that were i n c o r r e c t l y s i z e d were classed as being e i t h e r oversized or undersized; oversized p a r t i c l e s were p a r t i c l e s that should have f a l l e n into a shorter length f r a c t i o n whereas undersized TABLE V: Percent weight of p a r t i c l e s c o l l e c t e d i n each t h e o r e t i c a l p a r t i c l e length f r a c t i o n on the Forage P a r t i c l e Separator (FPS) that were c o r r e c t l y and i n c o r r e c t l y sized. THEORETICAL FPS OVER CORRECTLY UNDER LENGTH FRACTION SIZED SIZED SIZED <4 mm 0.0 56.8 b c 43.2 4-10 mm 23.1 65.9 C 11.0 10-20 mm 33.1 58.3 b c 8.7 20-40 mm 42.9 52.1 a b 5.0 40-80 mm 42.9 53.4 b c 3.7 >80 mm 64.5 39.6 a 0.0 a _ c Values f o r c o r r e c t l y s i z e d p a r t i c l e s with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -37- p a r t i c l e s were p a r t i c l e s that should have been c l a s s i f i e d into a longer length f r a c t i o n . As the gap s i z e on the FPS increased there was a s i g n i f i c a n t increase i n the proportion of oversized p a r t i c l e s and a decrease i n the proportion of undersized p a r t i c l e s c o l l e c t e d i n the respective p a r t i c l e length f r a c t i o n s . These r e s u l t s are consistent with observations made while operating the FPS. L o g i c a l l y i t was impossible f o r any p a r t i c l e to be oversized i n the smallest length f r a c t i o n or undersized i n the longest length f r a c t i o n . However, since many p a r t i c l e s had to cross a number of gaps before a r r i v i n g at the c o r r e c t l y s i z e d gap, one would expect an increased incidence of undersizing i n the smaller length f r a c t i o n s . This undersizing u s u a l l y r e s u l t e d from longer, i r r e g u l a r l y shaped p a r t i c l e s i n i t i a l l y clogging and then threading t h e i r way through the smaller gaps. Conversely, as the p a r t i c l e s passed down the FPS, the proportion of long to shorter p a r t i c l e s increased, increasing the p r o b a b i l i t y of o v e r s i z i n g from smaller p a r t i c l e s being " c a r r i e d " over the correct gap and f a l l i n g into the longer p a r t i c l e length f r a c t i o n s . Table VI shows the proportions of actual p a r t i c l e lengths i n the chopped forage samples, by weight, that were c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d by the FPS. The TLC d i d not have a s i g n i f i c a n t e f f e c t (P > 0.05) on the accuracy of p a r t i c l e length c l a s s i f i c a t i o n . The proportions of <4, 10-20, 20-40, 40-80 and >80 mm p a r t i c l e s that were c o r r e c t l y c l a s s i f i e d were not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) from each other but only averaged 63.5 percent. The proportion of c o r r e c t l y c l a s s i f i e d 4-10 mm p a r t i c l e s (38.7%) was s i g n i f i c a n t l y lower (P < 0.05). No explanation f o r t h i s d i f f e r e n c e could be found. As p a r t i c l e length increased the incidence of undersizing increased whereas the incidence of ove r s i z i n g decreased. Since longer p a r t i c l e s had to t r a v e l over a greater number of gaps than d i d shorter -38- TABLE VI: Percent weight of sample forage p a r t i c l e s of the given actual ranges of p a r t i c l e length that were c o r r e c t l y and i n c o r r e c t l y s i z e d by the Forage P a r t i c l e Separator. ACTUAL SAMPLE UNDER CORRECTLY OVER PARTICLE LENGTHS SIZED SIZED SIZED <4 mm 0.0 59. 8 b 40.2 4-10 mm 11.2 38.7 a 50.2 10-20 mm 8.3 61. 2 b 30.6 20-40 mm 15.6 61. 6 b 22.9 40-80 mm 18.6 69. 9 b 11.5 >80 mm 35.2 64. 8 b 0.0 a _ D Values for c o r r e c t l y s i z e d p a r t i c l e s with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). p a r t i c l e s , before being separated, there was a greater p r o b a b i l i t y f o r these p a r t i c l e s to erroneously f a l l through small gaps and be undersized. On the other hand, smaller p a r t i c l e s were more e a s i l y c a r r i e d or pushed by la r g e r p a r t i c l e s over the correct gap causing them to be oversized. The accuracy of p a r t i c l e length c l a s s i f i c a t i o n i n the forage samples as a whole, by weight, i s summarized i n table VII. The proportions of i n c o r r e c t l y c l a s s i f i e d p a r t i c l e s were divided into groups that passed through the f i r s t gap (1), or other gap (2), immediately preceding (-) or following (+) the correct gap. There was no s i g n i f i c a n t d i f f e r e n c e i n the accuracy of c l a s s i f i c a t i o n between TLC. An average of 56.6% of a l l p a r t i c l e s were c l a s s i f i e d c o r r e c t l y . Of the remaining i n c o r r e c t l y s i z e d p a r t i c l e s , 32.38% passed over the correct gap and through l a t e r gaps while 11.0% passed through gaps p r i o r to reaching t h e i r intended gap. Of those p a r t i c l e s passing over the correct gap, 91.1% f e l l through the immediately following gap while 75.0% of those dropping prematurely f e l l through the gap immediately preceding the corr e c t gap. This imbalance between over and undersizing by the FPS, on average, r e s u l t e d i n a net 21 percent ov e r s i z i n g of p a r t i c l e length. -39- TABLE VII: Percent weight of a l l p a r t i c l e s f a l l i n g into the correct tray (T Q) and into trays before (-) and a f t e r (+) the correc t tray on the FPS f o r mature orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC). TRAY TLC (mm) -2 + -1 T Q +1 +2 + 3.18* 2.6 8.8 54.9 29.9 3.8 6.35* 3.0 7.9 55.7 30.8 2.7 9.53* 2.5 8.4 58.5 28.2 2.4 mean* 2.7 8.3 56.6 29.5 2.9 Percentage of p a r t i c l e s f a l l i n g into trays a f t e r the correc t tray was s i g n i f i c a n l y greater (P < 0.05) than that f a l l i n g into trays before the correct tray. Gale and O'Dogherty (1982) also found a higher incidence of ov e r s i z i n g with t h e i r separator but i t was not as pronounced; the proportion of p a r t i c l e s c o r r e c t l y c l a s s i f i e d by t h e i r separator ranged from 65 to almost 100% i n some length f r a c t i o n s . These researchers also demonstrated with t h e i r separator, that the h o r i z o n t a l s e t t i n g of each gap width had to be 14.2% larger than h a l f the maximum length of p a r t i c l e intended to be separated by that gap. Therefore, i f a gap i s set at 5 mm, the t h e o r e t i c a l maximum length of p a r t i c l e capable of being separated w i l l not be 10 mm but somewhat les s than 10 mm depending on the c h a r a c t e r i s t i c s of the separator. For t h i s reason, a separator can be c a l i b r a t e d by c a l c u l a t i n g the t h e o r e t i c a l range of p a r t i c l e lengths being separated based on the degree of under or ove r s i z i n g . Based on the r e s u l t s above, the FPS was r e c a l i b r a t e d to correct f o r the 21% o v e r s i z i n g . The c a l i b r a t i o n was based on p a r t i c l e s having an equal p r o b a b i l i t y of being undersized or oversized. Therefore the t h e o r e t i c a l lengths of p a r t i c l e s c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on the FPS were reduced by 21% to the following: <3.3, 3.3-8.25, 8.25-16.5, 16.5-33.0, -40- 33.0-66.0, and >66.0 mm. By reducing the upper l i m i t s of p a r t i c l e s i z e by 21%, the net adjustment i n the range of p a r t i c l e lengths c o l l e c t e d i s 10.5%. For example, with two consecutive gaps set to t h e o r e t i c a l l y separate p a r t i c l e s up to 10 mm and 20 mm i n length re s p e c t i v e l y , the 20 mm f r a c t i o n loses 3.50 mm of l a r g e r p a r t i c l e lengths but gains 1.75 mm of smaller p a r t i c l e lengths r e s u l t i n g i n an o v e r a l l adjustment of 10.5% on e i t h e r side. The actual proportion of sample p a r t i c l e s i n each of these new p a r t i c l e length f r a c t i o n s was then c a l c u l a t e d by i n t e r p o l a t i n g the r e s u l t s from v i s u a l separation. A f t e r c a l i b r a t i o n of the t h e o r e t i c a l length of p a r t i c l e s c o l l e c t e d i n each f r a c t i o n on the FPS, there was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) between the FPS and v i s u a l l y determined p a r t i c l e length d i s t r i b u t i o n s of a l l samples tested (Table V I I I ) . In general the Chi squared values f o r goodness of f i t were considerably reduced i n d i c a t i n g a greater s i m i l a r i t y between the two d i s t r i b u t i o n s . There was, however, s t i l l a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) between FPS p a r t i c l e length f r a c t i o n s i n the proportion of c o r r e c t l y c l a s s i f i e d p a r t i c l e s i n each f r a c t i o n (Table IX). The accuracy of c l a s s i f i c a t i o n tended to be more uniform, however, with a s i g n i f i c a n t decrease (P < 0.05) i n the accuracy of c l a s s i f i c a t i o n i n the shorter p a r t i c l e length f r a c t i o n s and a s i g n i f i c a n t increase (P < 0.05) i n the accuracy i n the longer p a r t i c l e length f r a c t i o n s . The d i s t r i b u t i o n of undersized, c o r r e c t l y sized, and oversized p a r t i c l e s within f r a c t i o n s was s h i f t e d s i g n i f i c a n t l y (P < 0.05) from o v e r s i z i n g to undersizing i n the 3.3-8.25, 8.25-16.5, 16.5-33.0 and 33.0-66.0 mm f r a c t i o n s . This s h i f t was consistent with the objective of c a l i b r a t i o n . There was a s i m i l a r increase i n o v e r s i z i n g and decrease i n undersizing as gap s i z e increased as there was before c a l i b r a t i o n . -41- TABLE VIII: P a r t i c l e length d i s t r i b u t i o n s (percent of sample weight) of mature orchardgrass hay, chopped at three t h e o r e t i c a l lengths of cut (TLC), determined by the Forage P a r t i c l e Separator(FPS) and by v i s u a l (VIS) separation a f t e r c a l i b r a t i o n of the FPS. CALIBRATED PARTICLE LENGTH RANGE (mm) TLC (mm) <3. .3 3. .3- 8. .3- 16. ,5- 33. ,0- >66.0 CHI 2 8. .3 16. .5 33. .0 66. .0 3.18 FPS 15. .9 18. .7 30. .3 22. .8 10. .5 2.0 1.204 VIS 15. .0 21. .5 26. .4 25. .1 9. .7 2.4 6.35 FPS 10. .8 15. .5 35. .1 23. .5 12, .8 2.5 5.043 VIS 6, .9 22, .5 30, .5 24, .3 12, .1 3.7 9.53 FPS 7, .5 9, .7 37, .6 29, .2 13, .9 2.1 3.210 VIS 5, .1 14, .1 33, .1 30, .0 14, .9 2.8 mean FPS 10, .9 14, .1 34, .7 25, .6 12, .6 2.2 2.551 VIS 8. .6 18, .9 30, .3 26. .8 12, .5 3.0 Table X gives the proportions of the new ranges of actual p a r t i c l e length i n a whole sample that were c o r r e c t l y and i n c o r r e c t l y c l a s s i f i e d by the FPS. The accuracy of c l a s s i f i c a t i o n of each of these ranges of p a r t i c l e TABLE IX: Percent weight of p a r t i c l e s , c o l l e c t e d i n each t h e o r e t i c a l p a r t i c l e length f r a c t i o n on the Forage P a r t i c l e Separator (FPS) that were c o r r e c t l y and i n c o r r e c t l y s i z e d a f t e r c a l i b r a t i o n . THEORETICAL FPS OVER CORRECTLY UNDER LENGTH FRACTION SIZED SIZED SIZED <3.30 mm 0, .0 46, ,8 a 53, .2 3, .30- 8.25 mm 19. .1 50. . l a 30. .9* 8, .25-16.50 mm 24. .1 55. ,0 a b 21. .0* 16, .50-33.00 mm 24. .2 63. ,4b 11. .9* 33, .00-66.00 mm 23. .3 65. ,4b 11. .3* >66.00 mm 33. .7 66. ,3 b 0, .0 Values f o r c o r r e c t l y s i z e d p a r t i c l e s with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). D i s t r i b u t i o n of c o r r e c t l y and i n c o r r e c t l y s i z e d p a r t i c l e s within p a r t i c l e length f r a c t i o n was s i g n i f i c a n t l y d i f f e r e n t than that before c a l i b r a t i o n (P < 0.05),. -42- TABLE X: Percent weight of sample forage p a r t i c l e s of the given actual ranges of p a r t i c l e length that were c o r r e c t l y and i n c o r r e c t l y s i z e d by the Forage P a r t i c l e Separator a f t e r c a l i b r a t i o n . ACTUAL SAMPLE PARTICLE LENGTHS UNDER SIZED CORRECTLY SIZED OVER SIZED <3.30 mm 3.30- 8.25 mm 8.25-16.50 mm 16.50-33.00 mm 33.00-66.00 mm >66.00 mm 0.0 15.9 19.2 29.0 30.0 51.1 59.8 b c 38.0 a 62.9 C 60.9 b c 65. 7 C 48.9 a b 40.2 46.2 18.0* 10.1* 4.5 0.0* c Values for c o r r e c t l y s i z e d p a r t i c l e s with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). D i s t r i b u t i o n of c o r r e c t l y and i n c o r r e c t l y s i z e d range of p a r t i c l e length was s i g n i f i c a n t l y d i f f e r e n t than that before c a l i b r a t i o n (P > 0.05). length was not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) from that f o r the previously given ranges of p a r t i c l e length (Table VI), with the exception of the longest p a r t i c l e s f o r which the proportion of c o r r e c t l y c l a s s i f i e d p a r t i c l e s declined from 64.8 to 48.9%. This f r a c t i o n , however, represented les s than 4% of a l l p a r t i c l e s that were separated. Within the ranges of p a r t i c l e length there was a s i g n i f i c a n t s h i f t (P < 0.05) from o v e r s i z i n g to undersizing with p a r t i c l e s ranging i n length from 8.25-16.5 mm and 16.5-33.0 mm. Undersizing of the l a r g e s t p a r t i c l e lengths (>66 mm) also s i g n i f i c a n t l y increased (P < 0.05). There was a s i m i l a r increase i n undersizing and decrease i n o v e r s i z i n g as p a r t i c l e length increased as there was before c a l i b r a t i o n . The accuracy of length c l a s s i f i c a t i o n of a l l p a r t i c l e s i n the samples as a whole, by weight, a f t e r c a l i b r a t i o n i s summarized i n Table XI. C a l i b r a t i o n d i d not s i g n i f i c a n t l y change (P > 0.05) the proportion of p a r t i c l e s c o r r e c t l y c l a s s i f i e d (57.3%) by the FPS. There was, however, a s i g n i f i c a n t s h i f t (P < 0.05) from oversizing, to undersizing of p a r t i c l e s such that -43- TABLE XI: Percent weight of a l l p a r t i c l e s f a l l i n g into the correct tray (T Q) and into trays before (-) and a f t e r (+) the corre c t tray, f o r mature orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC), a f t e r c a l i b r a t i o n of the Forage P a r t i c l e Separator. TRAY TLC (mm) -2+ -1 T Ao +1 +2+ 3.18 3.8 18.5 54.7 20.2 2.9 6.35 4.3 17.4 56.8 19.4 2.1 9.53 3.4 18.2 59.6 17.2 1.7 mean 3.8 18.0 57.3 18.7 2.1 there was no s i g n i f i c a n t difference (P > 0.05) between the proportion of p a r t i c l e s that were oversized and those that were undersized. Of the t o t a l weight of chopped forage that was separated, 57.3% of the p a r t i c l e s were c l a s s i f i e d c o r r e c t l y with 21.8% being undersized and 20.9% being oversized a f t e r c a l i b r a t i o n . I t was therefore concluded that the simple v i b r a t i n g tray separator s u f f e r s from an inherent i n a b i l i t y to accurately c l a s s i f y a l l the p a r t i c l e s i n a sample of chopped forage by length. The over and undersizing errors which occur, are i n part due to the design of the machine and i n part due to the d i f f i c u l t y of separating i r r e g u l a r l y shaped p a r t i c l e s using the p r i n c i p l e of overbalancing. On the other hand, due to the r e p r o d u c i b i l i t y of r e s u l t s and the a b i l i t y to c a l i b r a t e the t h e o r e t i c a l lengths of p a r t i c l e s that the separator c l a s s i f i e d into each f r a c t i o n , i t was concluded that the FPS could be used to accurately and q u a n t i t a t i v e l y determine the p a r t i c l e length d i s t r i b u t i o n of chopped forage. -44- DESCRIPTION OF PARTICLE LENGTH DISTRIBUTION Goodness of F i t of Mathematical Functions The c o e f f i c i e n t s of determination for the regression of percent cumulative weight undersize on p a r t i c l e length using the f i v e regression equations are shown i n Table XII. The modified Weibull function (5) c o n s i s t e n t l y gave the highest R 2 values, followed by the regression of "probit" Y on p a r t i c l e length (4). A l l c o e f f i c i e n t s of determination were s i g n i f i c a n t (P < 0.05) with the exception of those r e s u l t i n g from simple l i n e a r regression (1) with the data c o l l e c t e d using the Forage P a r t i c l e Separator. Figures 3a through 7b show the f i t of the predicted regression l i n e s TABLE XII: Average R^ values for the f i v e regression models f i t t e d to the data r e s u l t i n g from the Forage P a r t i c l e Separator (FPS) and v i s u a l (VIS) separation of mature orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC). REGRESSION EQUATION* METHOD TLC 1 2 3 4 5 3.18 0 600* 0 942 0 874 0 955 0 998 FPS 6.35 0 616* 0 942 0 870 0 956 0 995 9.53 0 630* 0 933 0 875 0 960 0 994 3.18 0 503 0 886 0 778 0 955 0 998 VIS 6.35 0 479 0 876 0 695 0 976 0 995 9.53 0 445 0 848 0 685 0 981 0 994 * 1: Y = a + bX 2: Y = a + blogX 3: logY = a + blogX 4: Probi t Y = a + blogX C -(BX) 5: Y = 100(1 - e ) * R 2 value not s i g n i f i c a n t (P > 0.05). -45- r e l a t i o n to the observed data, and the d i s t r i b u t i o n of re s i d u a l s f or each regression equation f o r the FPS separated orchardgrass hay that was chopped at a TLC of 3.18 mm. From these graphs i t i s c l e a r that equations 1 through 4 displayed a systematic lack of f i t to the observed data. The re s i d u a l s r e s u l t i n g from the use of equations 1, 2 and 3 were c o n s i s t e n t l y d i s t r i b u t e d i n an inverted "U" shape while those r e s u l t i n g from the use of equation 4 were c o n s i s t e n t l y d i s t r i b u t e d i n a normal "U" shape. When the data was f i t t e d to the modified Weibull function, however, the r e s i d u a l s were randomly d i s t r i b u t e d around the predicted regression l i n e i n d i c a t i n g a consistent goodness of f i t of the data to the predicted cumulative curve. A further goodness of f i t t e s t was performed by comparing the derived p a r t i c l e length p r o b a b i l i t y density d i s t r i b u t i o n s predicted from regression equations 2, 4 and 5 with those observed using FPS and v i s u a l separation. The Chi squared values from the analysis are shown i n Table XIII. There was a consistent lack of f i t (P < 0.05) between the observed and predicted p a r t i c l e length p r o b a b i l i t y density d i s t r i b u t i o n s using equation 2. The same lack of f i t was seen using equation 4 but only f o r the d i s t r i b u t i o n s that were determined using the FPS. This r e s u l t indicates that the actual d i s t r i b u t i o n of p a r t i c l e length i n chopped forage may approximate a lognormal d i s t r i b u t i o n . A s i m i l a r lack of f i t to the lognormal d i s t r i b u t i o n observed i n the data from FPS separation has been observed when d i s t r i b u t i o n s of elongated p a r t i c l e s were determined by s i e v i n g chopped forage (Waldo et a l . . 1971; A l l e n et a l . . 1984), rumen contents (Pond et a l . . 1984) and f e c a l samples ( A l l e n et a l . . 1984; Pond et a l . . 1984). The above r e s u l t s also suggest that a high c o e f f i c i e n t of determination i s not s u f f i c i e n t , by i t s e l f , to in d i c a t e a goodness of f i t to a given d i s t r i b u t i o n i f the R.2 value i s below 0.99. R 2 values between 0.90 and 0.95 have i n the -46- FIGURE 3: Plots of FPS separation data f o r low q u a l i t y orchardgrass hay chopped at a TLC of 3.18 mm showing the f i t of the observed points to the predicted l i n e (a) and the d i s t r i b u t i o n of res i d u a l s (b) using the regression equation Y = a + bX. -47- FIGURE 4: Plots of FPS separation data f o r low q u a l i t y orchardgrass hay chopped at a TLC of 3.18 mm showing the f i t of the observed points to the predicted l i n e (a) and the d i s t r i b u t i o n of residuals (b) using the regression equation Y = a + blogX. -48- FIGURE 5: Plots of FPS separation data f o r low q u a l i t y orchardgrass hay chopped at a TLC of 3.18 mm showing the f i t of the observed points to the predicted l i n e (a) and the d i s t r i b u t i o n of re s i d u a l s (b) using the regression equation logY — a + blogX. -49- (a) -30 L FIGURE 6: Plots of FPS separation data for low q u a l i t y orchardgrass hay chopped at a TLC of 3.18 mm showing the f i t of the observed points to the predicted l i n e (a) and the d i s t r i b u t i o n of r e s i d u a l s (b) using the regression equation Probit Y = a + blogX. -50- (a) 100 8 0 - CD N CO w. CD T5 C Z> •s 601- CD CO E O 4 0 - * 2 0 / 9 ( b ) © N CO l _ CD TJ C 3 E o + 3 0 + 2 0 + 10 0 - 10 - 2 0 e — i i i » ' ' 2 0 4 0 6 0 8 0 100 P a r t i c l e Length (mm) 1 2 0 * til • • • I I -r»- - 3 0 L FIGURE 7: Plots of FPS separation data f o r low q u a l i t y orchardgrass hay chopped at a TLC of 3.18 mm showing the f i t of the observed points to the predicted l i n e (a) and the d i s t r i b u t i o n of res i d u a l s (b) using the modified Weibull function. -51- TABLE XIII: Chi squared values f o r the goodness of f i t of the derived p a r t i c l e length p r o b a b i l i t y density d i s t r i b u t i o n s , predicted by three regression equations, to those observed a f t e r FPS and v i s u a l (VIS) separation of orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC). REGRESSION EQUATION* METHOD TLC 2 4 5 3.18 18.24* 15.62* 1.40 FPS 6.35 41.30* 15.36* 4.67 (n-6) 9.53 63.87* 23.71* 8.20 3.18 29.38* 8.61 0.87 VIS 6.35 60.90* 2.01 10.33 (n-24) 9.53 73.90* 6.32 8.77 # 2: Y = a + blogX 4: Probit Y = a + blogX C -(BX) 5: Y = 100(1 - e ) * CHI squared value s i g n i f i c a n t (P < 0.05). past been used as proof that c e r t a i n data approximated a lognormal d i s t r i b u t i o n (Smith et a l . . 1984). There was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05), however, between the observed and predicted p r o b a b i l i t y density d i s t r i b u t i o n s f o r both the FPS and v i s u a l separation data when the modified Weibull-type function (5) was used. P r e d i c t i o n of Median P a r t i c l e Length Table XIV gives the median p a r t i c l e lengths predicted by equations 2, 4 and 5 f o r the separation of the hay by the FPS and v i s u a l separation. The median p a r t i c l e lengths predicted from FPS data were based on the c a l i b r a t e d ranges of p a r t i c l e length that were c o l l e c t e d on the FPS. Due to the goodness of f i t of the modified Weibull function f o r both the cumulative p a r t i c l e length and p a r t i c l e length p r o b a b i l i t y density d i s t r i b u t i o n s , the -52- TABLE XIV: Median p a r t i c l e lengths predicted by three regression equations f o r FPS and v i s u a l l y (VIS) separated orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC). REGRESSION EQUATION* METHOD TLC 2 4 5 3.18 11.5 10.2 12.0 FPS 6.35 13.7 11.7 14.1 (n=6) 9.53 15.8 13.2 16.4 3.18 8.9 11.9 11.8 VIS 6.35 10.9 14.0 13.8 (n=24) 9.53 12.6 16.1 16.4 # 2: Y = a + blogX 4: Probit Y = a + blogX C -(BX) 5: Y = 100(1 - e ) predicted median p a r t i c l e lengths f o r the v i s u a l l y separated hay, determined using the Weibull function, were assumed to be the "correct" values, and the other values were s u b j e c t i v e l y compared with them. Lack of adequate r e p l i c a t i o n i n t h i s case d i d not permit s t a t i s t i c a l t e s t i n g of any dif f e r e n c e s . There was a good agreement between the median p a r t i c l e length values predicted from the FPS data and those predicted from v i s u a l separation data when the modified Weibull function was used. This r e s u l t further indicated that the FPS could be used to accurately quantitate the p a r t i c l e length d i s t r i b u t i o n i n chopped forage. There was also good agreement between the median p a r t i c l e length values predicted by regression equations 4 and 5 when applied to the v i s u a l separation data. However, the f i t t i n g of the lognormal d i s t r i b u t i o n to FPS determined p a r t i c l e length d i s t r i b u t i o n s tended to underestimate the median p a r t i c l e lengths of these d i s t r i b u t i o n s due to a consistent lack of f i t as indicated i n Table XIII. These r e s u l t s support -53- other research that has shown that the goodness of f i t of the lognormal d i s t r i b u t i o n to s i e v i n g data by l i n e a r regression may be a f f e c t e d by the s e l e c t i o n of sieves sizes that are used during separation or when points are missing from e i t h e r end of the cumulative d i s t r i b u t i o n ( A l l e n et a l . . 1984). These researchers demonstrated that a b e t t e r f i t to separation data may be obtainable by using maximum l i k l i h o o d estimators of the lognormal d i s t r i b u t i o n parameters. F i t t i n g of data by non-linear regression as i s done using the Weibull funct ion or the Gamma function i s not subject to the same f i t t i n g e rrors as i s l i n e a r regression ( A l l e n et a l . . 1984). Although the median p a r t i c l e lengths predicted by equation 2 were s i m i l a r to the "correct" values, the lack of f i t of t h i s equation to the data suggests that the r e s u l t s were obtained by coincidence. Only regression using the modified Weibull function r e s u l t e d i n predicted p a r t i c l e length p r o b a b i l i t y density functions that were s i m i l a r to those that were observed using e i t h e r FPS or v i s u a l separation data. Murphy and Bohrer (1984) have argued that no e x p l i c i t theory e x i s t s regarding comminution leading to the production of a Rosin-Rammler (or Weibull) d i s t r i b u t i o n of p a r t i c l e sizes and for that reason concluded that i t s use was inappropriate f o r describing the p a r t i c l e s i z e d i s t r i b u t i o n of comminuted substances. However, as these researchers also pointed out, the Rosin-Rammler or Weibul function i s also the s o l u t i o n of the d i f f e r e n t i a l "hazard rate" equation and the p r o b a b i l i t y function proposed by Weibull (1951) f o r material f a i l u r e ; both of these c h a r a c t e r i s t i c s are involved i n the comminution of feed p a r t i c l e s by hammering, grinding, chopping and chewing. Therefore, the use of the Weibull function appears to be appropriate f o r describing the p a r t i c l e length d i s t r i b u t i o n i n chopped forages when they have been separated on a simple v i b r a t i n g tray separator. -54- No methods, however, have been proposed f o r the d e s c r i p t i o n of the spread of p a r t i c l e lengths i n a sample of chopped forage using t h i s function. D e s c r i p t i o n of Spread Using the Weibull Function One of the major benefits of using the lognormal d i s t r i b u t i o n i s that the d i s t r i b u t i o n of p a r t i c l e lengths can be described by two parameters, the log mean and log standard deviation. However, since the lognormal d i s t r i b u t i o n d i d not s a t i s f a c t o r i l y f i t the data from FPS separation, a method of describing the spread of p a r t i c l e s using the Weibull function was required. I f one examines the act i o n of the parameters i n the Weibull function (Figure 8), one can see that the B parameter controls the s h i f t of the curve ( i e . change i n curve p o s i t i o n from l e f t to r i g h t on the X axis) while the C parameter controls the shape ( i e . the r e l a t i v e slope and symmetry of the curve). When base "e" i s used i n the function, a change i n the shape parameter (C) causes the curve to pivo t around the 63.2 p e r c e n t i l e point. Therefore, both the B and C parameters must change when e i t h e r the median of a given p a r t i c l e length d i s t r i b u t i o n changes or the d i s t r i b u t i o n of p a r t i c l e lengths around a given median changes. However, when base 2 i s used i n the Weibull function (Figure 9), the pivo t point f o r changes i n the shape of a curve becomes the 50 p e r c e n t i l e point or the median p a r t i c l e length value f o r a given d i s t r i b u t i o n . The use of a d i f f e r e n t base changes the values of the two parameters but does not a l t e r the f i t of the function. By using base 2, changes i n the shape parameter (C) do not a l t e r the value of the s h i f t parameter (B) which can then be used to c a l c u l a t e the median p a r t i c l e length, the value of which i s determined by 1/B. -55- 0 1 0 2 0 3 0 4 0 5 0 6 0 Particle Length (mm) FIGURE 8: Changes i n shape of the modified Weibull cumulative frequency d i s t r i b u t i o n with various B and C parameter values when "base e" i s used i n the equation. -56- Particle Length (mm) FIGURE 9 : Changes i n shape of the modified Weibull cumulative frequency d i s t r i b u t i o n with various B and C parameter values when "base 2" i s used i n the equation. -57- The shape of a cumulative curve i s determined by the shape of the associated increment or density function. Therefore when base 2 was used i n the Weibull function, the value of the C parameter could be used to describe the shape of the p a r t i c l e length d i s t r i b u t i o n when applied to separation data. The e f f e c t of changing the value of the C parameter on the shape of the cumulative and derived increment (density) curves when base 2 was used i n the function i s shown i n Figures 10 and 11 r e s p e c t i v e l y ; a l l the curves have the same value f o r B and therefore p r e d i c t the same median p a r t i c l e length. With C equal to 1.0, the cumulative curve i s the same as a simple exponential curve. However, as the value of the C parameter increases, one can see that the incremental d i s t r i b u t i o n becomes les s skewed to the r i g h t such that when C i s equal to 3.212, a normal d i s t r i b u t i o n i s approximated. I f the value of C becomes even larger, the d i s t r i b u t i o n then becomes skewed to the l e f t . Therefore, i f two p a r t i c l e length d i s t r i b u t i o n s have the same median, but d i f f e r e n t C values, the spread of the p a r t i c l e s around the mean must be d i f f e r e n t ; and therefore, the two d i s t r i b u t i o n s must be d i f f e r e n t . Furthermore, as can be seen from Figure 10, as the value of C increases to 3.212, the r e l a t i v e spread of the p a r t i c l e s around the median decreases. I f two d i s t r i b u t i o n s have d i f f e r e n t median values, but s i m i l a r values of C, the r e l a t i v e spread of p a r t i c l e s around each mean i s equal. For example, two d i s t r i b u t i o n s have median p a r t i c l e lengths of 10 and 20 mm r e s p e c t i v e l y and the value of C i s 1.5 for both d i s t r i b u t i o n s . Using the values of B (0.1 and 0.05) and the value of C i n the Weibull function, one can c a l c u l a t e the range i n length of p a r t i c l e s c o l l e c t e d between the 25 and 75 p e r c e n t i l e points of the cumulative d i s t r i b u t i o n using the following equation: -58- 0 1 0 2 0 3 0 4 0 5 0 6 0 Particle Length (mm) FIGURE 10: Changes i n shape of the modified Weibull cumulative frequency d i s t r i b u t i o n given a f i x e d B parameter value and three C parameter values when "base 2" i s used i n the equation. -59- FIGURE 11: Changes i n shape of. the modi f i e d W e i b u l l p r o b a b i l i t y d e n s i t y d i s t r i b u t i o n given a f i x e d B parameter value and three C parameter values when "base 2" i s used i n the equation. -60- Hog ( - (log (Y - 1 W log 2)) | C X 10 B where: X the l e n g t h o f p a r t i c l e s a t the 25 o r 75 p e r c e n t i l e p o i n t . Y the p e r c e n t i l e p o i n t d i v i d e d by 100 C the shape parameter B the s h i f t parameter which i s e q u a l t o the i n v e r s e o f the median p a r t i c l e l e n g t h . The range o f p a r t i c l e l e n g t h s between the 25th and 75th p e r c e n t i l e p o i n t s f o r the two example p a r t i c l e l e n g t h d i s t r i b u t i o n s a r e 5.56 - 15.87 mm and 11.13 - 31.75 mm r e s p e c t i v e l y . E x p r e s s i n g the range o f l e n g t h s as a s i n g l e v a l u e (10.31 and 20.62 mm) and d i v i d i n g by the r e s p e c t i v e median p a r t i c l e l e n g t h g i v e s the r e l a t i v e s p r e a d o f p a r t i c l e l e n g t h s around the mean (1.031 and 1.031) which a r e e q u i v a l e n t f o r the two p a r t i c l e l e n g t h d i s t r i b u t i o n s . T h e r e f o r e , the C parameter a c t s n o t o n l y as an i n d i c a t o r o f the shape o f the d i s t r i b u t i o n (normal v s . degree o f skewness) b u t i n a manner s i m i l a r t o the c o e f f i c i e n t o f v a r i a t i o n i n d e s c r i b i n g the r e l a t i v e s p r e a d o f d i s t r i b u t i o n s h a v i n g the same o r d i s s i m i l a r median p a r t i c l e l e n g t h s . F o r t h i s r e a s o n the C parameter c a n be u s e d t o d e s c r i b e and t e s t the r e l a t i v e s p r e a d o f p a r t i c l e l e n g t h s around the median p a r t i c l e l e n g t h o f chopped f o r a g e s and was t h e r e f o r e named the c o e f f i c i e n t o f s p r e a d . T a b l e XV g i v e s the c o e f f i c i e n t s o f s p r e a d from the FPS and v i s u a l s e p a r a t i o n o f chopped o r c h a r d g r a s s hay. FPS s e p a r a t i o n t e n d e d t o o v e r e s t i m a t e the c o e f f i c i e n t o f s p r e a d f o r the p a r t i c l e l e n g t h d i s t r i b u t i o n s . T h i s i n d i c a t e d t h a t a l t h o u g h the FPS c o u l d be used t o a c c u r a t e l y determine the median p a r t i c l e l e n g t h s o f the d i s t r i b u t i o n s , some e r r o r may o c c u r i n the d e t e r m i n a t i o n o f shape o f the d i s t r i b u t i o n . I t i s -61- TABLE XV: C o e f f i c i e n t s of spread f o r orchardgrass hay chopped at three t h e o r e t i c a l lengths of cut (TLC) as determined from FPS and v i s u a l (VIS) separation. THEORETICAL LENGTH OF CUT (mm) 3.18 6.35 9.53 FPS 1.142 1.275 1.524 VIS 1.068 1.132 1.289 more l i k e l y , however, that the separation into many more p a r t i c l e length f r a c t i o n s by v i s u a l separation may have re s u l t e d i n a more accurate f i t t i n g of the Weibull function to the d i s t r i b u t i o n s . -62- SUMMARY The research i n t h i s chapter inves t iga ted the accuracy of a simple v i b r a t i n g t ray Forage P a r t i c l e Separator (FPS) i n separat ing forage p a r t i c l e s on the bas i s of l ength , and the d e s c r i p t i o n of the r e s u l t i n g p a r t i c l e length d i s t r i b u t i o n s us ing mathematical funct ions . By comparison with v i s u a l separat ion , the FPS c o r r e c t l y c l a s s i f i e d only 57.3 percent of the separated p a r t i c l e s , by weight, on the bas i s of l ength . However, a f t er c a l i b r a t i o n of the t h e o r e t i c a l p a r t i c l e lengths be ing separated in to f r a c t i o n s on the FPS, there was an equal degree of o v e r s i z i n g and u n d e r s i z i n g such that the FPS accurate ly descr ibed the p a r t i c l e length d i s t r i b u t i o n i n the chopped forage that was separated. Of the mathematical funct ions that were tes ted , the lognormal d i s t r i b u t i o n and the Weibul l func t ion both s i g n i f i c a n t l y f i t the p a r t i c l e length d i s t r i b u t i o n s that were determined by v i s u a l separat ion . Based on the d i s t r i b u t i o n of r e s i d u a l s from regres s ion , however, the Weibu l l func t ion gave the best f i t to the data . When us ing FPS separat ion data, the determined p a r t i c l e length d i s t r i b u t i o n s d i d not approximate a lognormal d i s t r i b u t i o n . This was probably due to problems assoc ia ted with f i t t i n g the lognormal d i s t r i b u t i o n by simple l i n e a r regres s ion . The Weibu l l f u n c t i o n , on the other hand, f i t the FPS and v i s u a l separat ion data equa l ly w e l l . Therefore i t was concluded that the Weibul l func t ion was more appropriate than the lognormal d i s t r i b u t i o n for use i n d e s c r i b i n g the p a r t i c l e length d i s t r i b u t i o n i n chopped forage. A method for d e s c r i b i n g the spread of p a r t i c l e length d i s t r i b u t i o n s us ing the C parameter of the modif ied Weibul l f u n c t i o n was descr ibed . -63- CHAPTER II THE EFFECT OF PROCESSING METHOD AND FORAGE TYPE ON THE PARTICLE LENGTH DISTRIBUTION OF DM, CP AND ADF IN PROCESSED FORAGES INTRODUCTION The reduction of p a r t i c l e s i z e i n forages fed to ruminants by chopping and grinding reduces feed wastage, can increase voluntary feed consumption, and has been shown to have an e f f e c t on di g e s t i o n and rate of passage of these feeds. Processing of d i f f e r e n t forages using i d e n t i c a l methods, has therefore r o u t i n e l y been used i n experimentation i n v e s t i g a t i n g the d i g e s t i b i l i t y of d i f f e r e n t forage types and the e f f e c t of p a r t i c l e s i z e on di g e s t i o n processes. L i t t l e research, however, has been done to see i f s i m i l a r p a r t i c l e s i z e d i s t r i b u t i o n s are produced when d i f f e r e n t forages are processed using the same method. Recent research has shown that d i f f e r e n t forages, ground under i d e n t i c a l conditions, can r e s u l t i n the production of s i g n i f i c a n t l y d i f f e r e n t p a r t i c l e s i z e d i s t r i b u t i o n s (Osbourn et a l . . 1981), and that the crude p r o t e i n (CP) and f i b e r f r a c t i o n s of the forage can be d i f f e r e n t i a l l y d i s t r i b u t e d throughout the range of p a r t i c l e sizes that are produced (Jaster and Murphy, 1983) . I f these differences i n p a r t i c l e s i z e d i s t r i b u t i o n of dry matter (DM), CP, and f i b e r are large enough within or between forages when processed under i d e n t i c a l conditions, lack of q u a n t i f i c a t i o n of the p a r t i c l e s i z e d i s t r i b u t i o n s could introduce uncontrolled v a r i a t i o n into experimental r e s u l t s . Therefore, the objective of the following study was to q u a n t i t a t i v e l y determine the e f f e c t of processing method (hammermilling or chopping at -64- three t h e o r e t i c a l lengths of cut [TLC]) and forage type ( a l f a l f a and h i g h and low q u a l i t y orchardgrass hay) on the p a r t i c l e l e n g t h d i s t r i b u t i o n of DM, CP, and a c i d detergent f i b e r (ADF) i n processed forage. -65- LITERATURE REVIEW Research has shown that the rate of microbial digestion, rate of passage and, therefore, the extent of di g e s t i o n of feedstuffs fed to ruminants may be d i r e c t l y a f f e c t e d by the p a r t i c l e s i z e d i s t r i b u t i o n i n the feed. Robles et a l . (1980) found that decreasing the p a r t i c l e s i z e of forages increased the rate of i n v i t r o c e l l w all d i g e s t i o n i n a l f a l f a . When various concentrates were subjected to i n v i t r o and i n s i t u digestion, Ehle et a l . (1982) found that the p a r t i c l e s i z e of li n s e e d meal had an e f f e c t on the rate of DM d i g e s t i b i l i t y whereas the p a r t i c l e s i z e of the other concentrates d i d not. P a r t i c l e s i z e , however, d i d not appear to a f f e c t the i n v i t r o or i n s i t u d i g e s t i o n of CP. The p a r t i c l e s i z e of feedstuffs appears to have i t s greatest e f f e c t on the rate of passage of p a r t i c l e s from the rumen, which i n turn a f f e c t s the d i g e s t i b i l i t y of the d i e t . Jaster and Murphy (1983), when feeding a l f a l f a hay to H o l s t e i n h e i f e r s , found that reducing the median p a r t i c l e length from 2160 to 1440 um (determined by sieving) s i g n i f i c a n t l y decreased DM and ADF d i g e s t i b i l i t y . Osbourn et a l . (1981) found that differences as small as 0.2 i n the Moduli of Fineness f o r d i f f e r e n t ground forages s i g n i f i c a n t l y a l t e r e d the organic matter and c e l l w all d i g e s t i b i l i t y of the forages when fed to lambs. Therefore, under c e r t a i n conditions, a r e l a t i v e l y small difference i n p a r t i c l e s i z e can s i g n i f i c a n t l y a f f e c t the d i g e s t i b i l i t y and rate of passage of some feedstuffs i n ruminants. Any study of the e f f e c t of forage p a r t i c l e s i z e on parameters of di g e s t i o n and rate of passage i n ruminants u s u a l l y requires that the fe e d s t u f f f i r s t be processed. Processing of forages i s also used to reduce feed wastage and increase voluntary feed consumption when conducting -66- research studying the e f f e c t of d i f f e r e n t forage c h a r a c t e r i s t i c s on forage u t i l i z a t i o n . In most of these t r i a l s , the d i f f e r e n t feedstuffs have been processed using the same method, but the actual p a r t i c l e s i z e d i s t r i b u t i o n s of the processed feedstuffs have not been determined; only the methods employed, in c l u d i n g screen s i z e used i n grinding or hammermilling, or the t h e o r e t i c a l length of cut (TLC) used during chopping, are reported. Osbourn et a l . (1981), however, found that d i f f e r e n t forages, harvested with the same equipment, m i l l e d through the same s i z e screen and/or passed through the same p e l l e t i z e r had s i g n i f i c a n t l y d i f f e r e n t Moduli of Fineness. The researchers also found that the differences i n the p a r t i c l e s i z e d i s t r i b u t i o n s between forages processed by an i d e n t i c a l method s i g n i f i c a n t l y a f f e c t e d the comparison of the d i g e s t i b i l i t y of these forages. Similar research i n v o l v i n g the chopping of forages could not be found. The p a r t i c l e s i z e d i s t r i b u t i o n s of forages reported i n the l i t e r a t u r e are based on the d i s t r i b u t i o n of DM. I f pr o t e i n and f i b e r are evenly d i s t r i b u t e d , by weight, throughout the range of p a r t i c l e s i z e s i n a sample of processed forage, the p a r t i c l e s i z e d i s t r i b u t i o n s of DM, CP and ADF w i l l be s i m i l a r . I f the concentration of CP or ADF changes as p a r t i c l e s i z e changes, the d i s t r i b u t i o n of these nutrients on the basis of p a r t i c l e s i z e w i l l be d i f f e r e n t from the p a r t i c l e s i z e d i s t r i b u t i o n of DM. The processing of d i f f e r e n t feedstuffs using the same method does appear to d i f f e r e n t i a l l y a f f e c t the d i s t r i b u t i o n s of CP and ADF i n r e l a t i o n to p a r t i c l e s i z e . Ehle (1984) found that the concentration of c e l l w all components increased with increasing p a r t i c l e s i z e within a sample of coarse chopped a l f a l f a and two maturities of smooth bromegrass hay. He also found that the rate of increase was greater i n the a l f a l f a hay than i t was i n the bromegrass hays, wi t h i n which the rate of increase was greater i n the more -67- mature bromegrass hay. Jaster and Murphy (1983) also found that the ADF concentration of chopped a l f a l f a hay p a r t i c l e s within a given sample increased as p a r t i c l e s i z e increased. They also demonstrated that crude p r o t e i n concentration decreased with increasing p a r t i c l e s i z e . Therefore, the p a r t i c l e s i z e d i s t r i b u t i o n s of DM, CP and ADF may d i f f e r w i t h i n samples of processed forage and between forages processed under i d e n t i c a l conditions. I f these differences are large enough, they also could have a s i g n i f i c a n t e f f e c t on the comparison of the d i g e s t i b i l i t y and rate of passage of d i f f e r e n t forages and the determination of the e f f e c t of reducing forage p a r t i c l e s i z e on the process of d i g e s t i o n i n the ruminant. ( -68- MATERIALS AND METHODS PROCESSING AND PARTICLE LENGTH SEPARATION OF FORAGE Approximately 100 kilograms each of baled a l f a l f a (ALF) and high and low q u a l i t y orchardgrass hay (OGH and OGL) were chopped at three t h e o r e t i c a l lengths of cut (TLC) (3.18, 6.35 and 9.53 mm), with a John Deere, Model 35 forage harvester, and hammer-milled through a 12.7 mm screen i n a Haybuster. The bales of each forage were broken open and the sheaves equally and randomly d i s t r i b u t e d between the four processing treatments i n a balanced three by four f a c t o r i a l design. The sheaves for each chopped, forage treatment were then chopped and sampled three times using the same procedure that was described i n Chapter 1. Hammermilled forage was c o l l e c t e d d i r e c t l y below the hammermill screen, mixed and then sampled three times by "grab sampling" with a small shovel. Each hammermilled sample was a composite of not l e s s than s i x randomly selected subsamples. Grab samples of a l l processed forage were also taken and composited for each forage type to be used f o r chemical a n a l y s i s . A l l samples, excluding those f o r chemical analysis, were then separated into 6 p a r t i c l e length f r a c t i o n s (<3.3, 3.3-8.25, 8.25-16.5, 16.5-33.0, 33.0-66.0 and >66.0 mm) on the Forage P a r t i c l e Separator (FPS) as described i n Chapter 1. CHEMICAL ANALYSIS A f t e r separation, s i m i l a r p a r t i c l e length f r a c t i o n s from samples within each treatment combination were composited to y i e l d a s i n g l e set of p a r t i c l e length f r a c t i o n s f o r each treatment combination. These composite p a r t i c l e -69- length f r a c t i o n s and the unseparated forage samples were then ground through a 1.0 mm screen i n a Wiley m i l l before being analyzed f o r dry matter (DM) (oven drying at 65 degrees C e l s i u s ) , crude p r o t e i n (CP) (Parkinson and A l l e n , 1975) and Ac i d Detergent Fiber (ADF) (Waldern, 1971) content. CALCULATIONS The weight of CP and ADF i n each p a r t i c l e length f r a c t i o n of a given sample was c a l c u l a t e d by mu l t i p l y i n g the weight of the sample c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on the FPS by the respective n u t r i t i o n a l content of the f r a c t i o n . The percent weight of CP and ADF i n each f r a c t i o n was then c a l c u l a t e d . The median p a r t i c l e length (MPL) and c o e f f i c i e n t of spread (CS) of DM, CP, and ADF f o r each sample were determined by the methods described i n Chapter 1 using the Modified Weibull function. The MPL for each n u t r i e n t i n a forage sample i s defined as the length at which 50% of the cumulative percent weight of the nutri e n t i s found. For example, i f the DM MPL i s 10 mm, 50% of the t o t a l weight of DM i n the sample i s located i n the p a r t i c l e s that are les s than 10 mm i n length and 50% of the DM i s located i n the p a r t i c l e s greater than 10mm i n length. The same applies f o r CP or ADF. I f the CP MPL i s 7 mm, 50% of the t o t a l weight of CP i n the sample i s located i n the p a r t i c l e s that are less than 7 mm i n length and 50% of the CP i s located i n the p a r t i c l e s greater than 7 mm i n length. The determination of the cumulative d i s t r i b u t i o n of CP and ADF was the same as that f o r DM except that the percent weight of each nutr i e n t was used i n place of the percent weight of DM. The MPL of each p a r t i c l e length f r a c t i o n of a given sample separated on -70- the FPS was determined by so l v i n g the appropriate regression equation for the independent v a r i a b l e X when the cumulative percent weight undersize (Y) was equal to the mid point of the cumulative sample weight c o l l e c t e d i n a given p a r t i c l e length f r a c t i o n . For example, i f the range of percent cumulative weight c o l l e c t e d i n a given tray was 65 to 79%, the mid point (Y) was 72% ((65 + 79) / 2). STATISTICAL ANALYSIS The e f f e c t of treatment combination on the MPL and CS of DM, CP and ADF was tested by General Linear Hypothesis using the BMDrlOV packaged program of the U n i v e r s i t y of B r i t i s h Columbia. The General Linear Hypothesis was as follows: Y l j k = u + F ± + Pj + FP i : J + E i J k where: ^ij'k = t b e dependent v a r i a b l e : MPL or CS. u = the o v e r a l l mean. F^ = the e f f e c t of the i ' t h type of forage. Pj = the e f f e c t of the j ' t h method of processing. F P -J J = the e f f e c t due to the i n t e r a c t i o n between the i ' t h type of forage and the j 1 t h method of processing. E^jk = the unexplained r e s i d u a l error associated with each sample. Differences between means for the treatment combinations were tested using Duncan's M u l t i p l e Range t e s t (a = 0.5). The r e l a t i o n s h i p between p a r t i c l e length and n u t r i t i o n a l content within each treatment combination was tested using l i n e a r regression. Both simple -71- l i n e a r (Y = a + bX) and c u r v i l i n e a r regression (Y = a + blogX) were used. The p a r t i c l e length f r a c t i o n MPL was the independent v a r i a b l e (X) and the percent n u t r i e n t content of the f r a c t i o n was the dependent v a r i a b l e (Y). Regression analysis was performed using the BMDP:IR packaged program a v a i l a b l e at the U n i v e r s i t y of B r i t i s h Columbia. The e f f e c t of treatment combination on the r e l a t i o n s h i p between p a r t i c l e length and nu t r i e n t content was tested by homogeneity of regression c o e f f i c i e n t s using the U.B.C. Computing Center packaged program, SL:TEST. Differences between regression c o e f f i c i e n t s and regression l i n e s were separated by Scheffe's multiple range t e s t which was also part of the same program. The e f f e c t of treatment combination on the deviation of CP and ADF median p a r t i c l e lengths and c o e f f i c i e n t s of spread from those of DM within each forage was tested using the same General Linear Hypothesis as was used above. The di f f e r e n c e between the MPL f o r DM and that f o r CP or ADF within each sample was c a l c u l a t e d by subtracting the value determined f o r DM from that determined f o r CP and f o r ADF. Individual t tests were used to t e s t the n u l l hypothesis that the difference between the DM and CP, and the DM and ADF median p a r t i c l e lengths, within each treatment combination, was not s i g n i f i c a n t l y d i f f e r e n t from zero. - 7 2 - RESULTS AND DISCUSSION FORAGE NUTRITIONAL COMPOSITION Forage CP and ADF Content The n u t r i t i o n a l composition of the three forages i s given i n Table XVI. The three forages that were processed had s i g n i f i c a n t l y d i f f e r e n t (P < 0.05) CP contents; the OGH hay had the highest CP content, OGL hay the lowest, while the CP content of ALF was intermediate. OGL and ALF had s i m i l a r ADF contents which were s i g n i f i c a n t l y higher (P < 0.05) than that f o r OGH. Relationship Between P a r t i c l e Length and Nutrient Content Figures 11 and 12 show the CP and ADF content of the p a r t i c l e length f r a c t i o n s i n each of the processed forages as an average of the values determined with each method of processing. Regressing the percent nut r i e n t content of the p a r t i c l e length f r a c t i o n s on the logarithm of the median p a r t i c l e lengths of those f r a c t i o n s gave a better f i t than d i d simple l i n e a r regression. TABLE X V I : Percent crude p r o t e i n (CP) and a c i d detergent f i b e r (ADF) content (DM basis) of the a l f a l f a (ALF) and high (OGH) and low (OGL) q u a l i t y orchardgrass hay used i n the experiment. HAY ALF OGH OGL CP 17.0 b 25. 8 C 5.8 a ADF 34. l b 20. 8 a 33. 2 b a-c Means wit h i n rows with d i f f e r e n t d i f f e r e n t (P < 0.05). superscripts were s i g n i f i c a n t l y CO 3 0 w CO 2 0 c "5 o CL 10 CD TJ 3 o 0 *o»o. \ — • , D • O G H A L F O G L j 2 0 4 0 6 0 P a r t i c l e Leng th (mm) 8 0 FIGURE 1 2 : P l o t of the average observed values and p r e d i c t e d r e g r e s s i o n l i n e s (Y = a + blogX) f o r the r e l a t i o n s h i p between crude p r o t e i n content (Y) and p a r t i c l e l e n g t h (X) i n processed a l f a l f a (ALF) and h i g h (OGH) and low (OGL) q u a l i t y orchardgrass hays. -74- ~ 50 .2 « CO XI 2 fl Q CD X) i i c CD CO L. CD «-> CD Q JO o < 40 30 20 9 • I " / * i • — - o 1 0 L ALF OGL ® OGH 20 40 60 Particle Length (mm) 80 FIGURE 13: Plot of the average observed values and predicted regression l i n e s (Y = a + blogX) f o r the r e l a t i o n s h i p between a c i d detergent f i b e r content (Y) and p a r t i c l e length (X) i n processed a l f a l f a (ALF) and high (OGH) and low (OGL) q u a l i t y orchardgrass hays. -75- TABLE XVII: Regression c o e f f i c i e n t s (b) for the regression* of percent CP and ADF content of p a r t i c l e length f r a c t i o n s on the DM median p a r t i c l e length of the f r a c t i o n f o r the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC). FORAGE NUTRIENT TLC ALF OGH OGL CP H 3.18 6.35 9.53 -9.543 c -7.144 b c -8.359 c -8.240 c -1.635 a b* -0.817 a * -1.793 a b 0.330 a * -3.461 a b -2.872 a b -2.380 a b -2.674 a b ADF H ' 3.18 6.35 9.53 14.250 b c 10.890 b c 14.510 c 14.210 c -3.033 a * 1.459 a * 0.176 a * 0.233 a * 0.700 a * 1.840 a * 1.230 a * 3.860 a b Y = a + blogX Means with d i f f e r e n t superscripts within n u t r i e n t rows were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). Regression c o e f f i c i e n t not s i g n i f i c a n t l y d i f f e r e n t from zero (P > 0.05). The regression (Y = a + blogX) c o e f f i c i e n t s f o r CP and ADF are given i n Table XVII. Not a l l of the regression c o e f f i c i e n t s were s i g n i f i c a n t . Within each forage, the regression c o e f f i c i e n t s f o r CP and ADF content were not s i g n i f i c a n t l y a f f e c t e d (P > 0.05) by the method of processing that was used. The regression c o e f f i c i e n t s f o r CP f o r a l l but one treatment combination were negative. This indi c a t e d that CP content of the forage p a r t i c l e s declined with increasing p a r t i c l e length. The CP content of forage p a r t i c l e s declined at a s i g n i f i c a n t l y greater rate (P < 0.05) with increasing p a r t i c l e length i n the processed ALF hay than i t d i d i n the orchardgrass hays. The regression c o e f f i c i e n t s f o r CP i n OGL were larger, but not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) than those f o r OGH. The regression c o e f f i c i e n t s f o r CP r e s u l t i n g from three of the processing -76- methods used on OGH, however, were not s i g n i f i c a n t l y d i f f e r e n t from zero (P > 0.05), i n d i c a t i n g that CP i n t h i s forage was uniformly d i s t r i b u t e d on the basis of p a r t i c l e length. The regression c o e f f i c i e n t s f o r ADF f o r a l l but one treatment combination were p o s i t i v e i n d i c a t i n g that the ADF content of forage p a r t i c l e s increased as p a r t i c l e length increased. This increase i n ADF content with increasing p a r t i c l e length was s i g n i f i c a n t l y greater (P < 0.05) i n processed ALF than i t was i n the orchardgrass hays. There was, however, no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) between the regression c o e f f i c i e n t s for OGH and OGL, and, with the exception of OGL hay chopped at a TLC of 9.53 mm, a l l of the ADF regression c o e f f i c i e n t s for these forages were not s i g n i f i c a n t l y d i f f e r e n t from zero (P > 0.05). PARTICLE LENGTH DISTRIBUTIONS Fitting of the Weibull Function The c o e f f i c i e n t s of determination for the f i t t i n g of the Weibull function to the cumulative p a r t i c l e length d i s t r i b u t i o n , by weight, of DM, CP and ADF i n a l l chopped forage were c o n s i s t e n t l y greater than 0.99. There was also a random d i s t r i b u t i o n of r e s i d u a l s around the regression l i n e s i n d i c a t i n g a good f i t of the function to the data. The c o e f f i c i e n t s of determination f o r the f i t t i n g of the Weibull function to the cumulative nu t r i e n t p a r t i c l e length d i s t r i b u t i o n s i n the hammered forage ranged from 0.97 to 0.99, which i s considered low f o r the p r e d i c t i o n of median p a r t i c l e length (MPL) and c o e f f i c i e n t of spread (CS) (see Chapter 1). The use of the Weibull function, however, re s u l t e d i n a random d i s t r i b u t i o n of r e s i d u a l s , and gave a better f i t to the data than d i d the lognormal d i s t r i b u t i o n . I t -77- was concluded, therefore, that the f i t of the Weibull function to the hammermilled forage data was adequate f o r the p r e d i c t i o n of MPL and CS i n th i s exp e r iment. DM Median Particle Length In most research in v o l v i n g the feeding of processed forage to ruminants, the p a r t i c l e s i z e d i s t r i b u t i o n s of d i f f e r e n t forages, processed using the same method, have been assumed to be s i m i l a r . In t h i s study, however, there was a s i g n i f i c a n t i n t e r a c t i o n (P > 0.05) between the e f f e c t s of forage type and method of processing on the DM MPL produced i n the processed forage (Table XVIII). F i r s t l y , the screen si z e used i n hammering or the TLC used i n chopping TABLE XVIII: DM, CP and ADF median p a r t i c l e lengths (mm) of the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC). FORAGE NUTRIENT TLC ALF OGH OGL SEM # H 4. 7 a 5. 6 a 8. lb DM 3.18 11. 2cd 8. 6 b 11. (jcde 0.6 6.35 10. 9 C 11. gcde 14. l f 9.53 13. 4 e f 12. g d e f 16. 4S H 3. 7 a 5. 4^ 6. 2b CP 3.18 8. 2 C 8. 4 C 8. 5 C 0.5 6.35 8. 3 C 11. 6de 10. 6 d 9.53 10. 3 d 12. 6 e 13. l e H 5. 9 a 5. 3 a 8. 2b ADF 3.18 13. 2de 8. 0 b 11. Qcd 0.5 6.35 12. gde 11. 0 C 14. 0 e f 9.53 15. 2 f g 11. g C d 16. 2S * Standard error of the mean f o r the values i n each n u t r i e n t row. a _ S Means with d i f f e r e n t superscripts within n u t r i e n t rows were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -78- was not an accurate p r e d i c t o r of the MPL that was produced when the forages were processed. In every case, the MPL of the hammered forage was less than the screen s i z e (12.7 mm) used, while the MPL of the chopped forage was greater than the TLC used during chopping. The net r e s u l t was that f o r each nutr i e n t , w i t h i n each forage, hammering through a 12.7 mm screen produced a s i g n i f i c a n t l y smaller (P < 0.05) MPL than d i d chopping at any TLC. Differences i n the mechanism of p a r t i c l e s i z e reduction between hammering and chopping determine the r e l a t i o n s h i p between the screen si z e or TLC and the MPL produced i n processed forage. The process of hammering forages involves p u l v e r i z a t i o n of p a r t i c l e s to a s i z e capable of passing through a given s i z e of screen. Because p u l v e r i z a t i o n r e s u l t s i n the production of a v a r i a b l e proportion of very small p a r t i c l e s , and there i s a l i m i t to the maximum s i z e of p a r t i c l e which can pass through the screen, the MPL of hammered forage w i l l be less than the s i z e of the screen aperture. When forages are chopped i n a p r e c i s i o n cut forage harvester, however, the MPL of the processed forage i s u s u a l l y greater than the TLC (O'Dogherty, 1982) . The c a l c u l a t i o n of a TLC assumes that p a r t i c l e s entering tha chopper pass through the blades end f i r s t and perpendicular to the c u t t i n g surface. In p r a c t i c e , forage p a r t i c l e s entering a chopper can be randomly oriented with respect to the c u t t i n g surface. P a r t i c l e s that do not pass through the blades perpendicular to the c u t t i n g surface w i l l be cut longer than the TLC. Therefore, the MPL of chopped forages u s u a l l y exceeds the c a l c u l a t e d TLC used during chopping. Processing of the d i f f e r e n t forages using the same methods d i d not always r e s u l t i n the production of s i m i l a r DM MPL between forages. There was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n the DM MPL between ALF and OGH when the forages were hammered or chopped at a TLC of 6.35 and 9.53 mm. When OGL -79- was processed by the same methods, however, the DM MPL produced i n each case was s i g n i f i c a n t l y l a r g e r (P < 0.05) than that produced when the other forages were processed. When the forages were chopped at a TLC of 3.18 mm, the r e l a t i o n s h i p between the DM MPL of the forages was changed; there was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n the DM MPL between ALF and OGL whereas the MPL produced when OGH was chopped was s i g n i f i c a n t l y smaller (P < 0.05). With each method of processing, the DM MPL produced when OGL was processed was s i g n i f i c a n t l y l a r g e r (P < 0.05) than that produced when OGH was processed. The reasons f o r the differences i n the DM MPL between forages processed by the same method are unclear. Robles et a l . (1980) found that the geometric mean diameter of ground forages generally increased with increasing c e l l wall content of the forages. The higher ADF content of OGL as compared with that of OGH may therefore have contributed to the production of la r g e r MPL i n the processed OGL. The morphological structure of forages may also contribute to differences i n MPL. Legumes are comprised of leaves and hollow stems which are more b r i t t l e than are the same components i n grasses ( H a l l et a l . . 1970). Therefore, e s p e c i a l l y when hammered, processed legumes should produce smaller MPL than that produced when grasses are processed by the same method. F i n a l l y , the presentation of p a r t i c l e s to the c u t t i n g surface i n a forage harvester has a d i r e c t e f f e c t on the length of p a r t i c l e s that are produced. Since each forage was chopped from the baled form, differences between forages i n the s t r u c t u r a l composition and o r i e n t a t i o n of p a r t i c l e s i n the bales may have contributed to d i f f e r e n c e s i n the DM MPL between d i f f e r e n t forages processed by the same method. No matter what the reason f o r the production of d i f f e r e n t MPL i n forages -80- processed by the same method, small differences between the DM p a r t i c l e size of forages fed to ruminants have been shown to have an e f f e c t on rate of passage, d i g e s t i b i l i t y and chewing behavior. San t i n i et a l . (1983) found that differences as small as 1 mm i n forage MPL d i r e c t l y and l i n e a r l y a f f e c t e d chewing time i n H o l s t e i n cows when they were fed chopped a l f a l f a hay and s i l a g e . Elimam and Orskov (1984) found that decreasing the Modulus of Fineness of ground d r i e d grass from 2.77 to 2.15 reduced the outflow of Chromium treated f i s h meal from the rumen. Decreasing the median p a r t i c l e length of chopped hay by approximately 5 mm, when fed to high producing dair y c a t t l e , decreased the amount of time the animals spent chewing and the ruminal acetate:propionate r a t i o (Van Beukelen et a l . . 1985). J a s t e r and Murphy (1983), when feeding a l f a l f a hay to H o l s t e i n h e i f e r s , found that reducing the geometric mean diameter from 2160 to 1440 um s i g n i f i c a n t l y decreased DM and ADF d i g e s t i b i l i t y but not t o t a l chewing times. Osbourn et a l . (1981) found that differences as small as 0.2 i n the moduli of fineness f o r d i f f e r e n t ground forages s i g n i f i c a n t l y a l t e r e d t h e i r O.M. and c e l l w all d i g e s t i b i l i t y when fed to lambs. The differences i n DM MPL between the forages processed by the same method i n t h i s study ranged from 0.5 to 3.5 mm. These differences i n MPL f a l l w i t h i n the range of sizes discussed above that have been shown to s i g n i f i c a n t l y a f f e c t forage u t i l i z a t i o n when processed forage i s fed to ruminants. Therefore, lack of q u a n t i f i c a t i o n of forage p a r t i c l e s i z e i n research using d i f f e r e n t forages processed by the same method may introduce uncontrolled experimental error. The above applies equally to research i n v e s t i g a t i n g the e f f e c t of reducing p a r t i c l e s i z e on the ruminant di g e s t i o n process, and to research i n v e s t i g a t i n g the u t i l i z a t i o n of d i f f e r e n t species and q u a l i t i e s of forage where processing i s used to reduce feed wastage and -81- increase voluntary feed intake. The above r e s u l t s , however, c l e a r l y show that with q u a n t i f i c a t i o n of forage p a r t i c l e s i z e , d i f f e r e n t processing methods can be used to produce s i m i l a r MPL i n d i f f e r e n t forages and thus reduce uncontrolled experimental error. The above r e s u l t s also showed that during chopping, each increase i n TLC di d not always r e s u l t i n an increase i n the DM MPL of chopped forage. When OGL was chopped, there was a s i g n i f i c a n t increase (P < 0.05) i n DM MPL with each increase i n TLC. There was also a s i g n i f i c a n t increase i n DM MPL when the TLC of ALF was increased from 6.35 to 9.35 mm and when the TLC of OGH was increased from 3.18 to 6.35 mm. However, increasing the TLC of ALF from 3.18 to 6.35 mm and the TLC of OGH from 6.35 to 9.53 mm d i d not r e s u l t i n the production of s i g n i f i c a n t l y d i f f e r e n t DM MPL (P > 0.05) between the TLC. Therefore, the preparation of dietary p a r t i c l e length treatments by chopping, on the basis of TLC alone, may not always ensure that a difference e x i s t s between the p a r t i c l e length d i s t r i b u t i o n s of the di e t a r y treatments. CP and ADF Median P a r t i c l e Length As with DM MPL, there was a s i g n i f i c a n t i n t e r a c t i o n (P < 0.05) between the e f f e c t s of forage and method of processing on the CP MPL,. and the ADF MPL, produced i n the processed forage. The e f f e c t of method of processing on the differences i n DM, CP and ADF MPL within each forage was s i m i l a r f o r each n u t r i e n t that was studied. The.nutrient MPL produced when a forage was hammered was always s i g n i f i c a n t l y smaller (P < 0.05) than that produced when the forage was chopped at any TLC. As with DM MPL, each increase i n the TLC of chopped OGL re s u l t e d i n a s i g n i f i c a n t increase (P < 0.05) i n CP MPL and ADF MPL; there was also no s i g n i f i c a n t difference (P > 0.05) between the MPL fo r each of the nutrients when ALF was chopped at a TLC of 3.18 and 6.35 mm -82- and when OGH was chopped at a TLC of 6.35 and 9.53 mm. The e f f e c t of method of processing on the differences i n DM, CP and ADF MPL between forages processed by the same method was d i f f e r e n t with each n u t r i e n t that was studied, whereas the DM MPL of ALF and OGH were s i m i l a r when the forages were hammered or chopped at a TLC of 6.35 or 9.53 mm, the CP MPL of ALF was s i g n i f i c a n t l y smaller (P < 0.05), and the ADF MPL s i g n i f i c a n t l y l a rger (P < 0.05) (except when hammered) than the respective n u t r i e n t MPL of OGH. The DM and the ADF MPL of OGL were s i g n i f i c a n t l y larger (P < 0.05) than the respective n u t r i e n t MPL of OGH but there was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n CP MPL between the two forages. When OGL and ALF were hammered or chopped at a TLC of 6.35 or 9.53 mm, the DM MPL and CP MPL of OGL were s i g n i f i c a n t l y l a rger (P < 0.05) than the respective n u t r i e n t MPL of ALF; the ADF MPL of the two forages, however, were not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) with each method of processing, except when the forages were hammered. The d i f f e r e n c e i n the e f f e c t of the treatment combinations on the DM, CP and ADF MPL produced i n the processed forage was caused by differences between forages i n the extent that n u t r i e n t MPL deviated from DM MPL within each foraqe. As with previous analyses, there was a s i g n i f i c a n t i n t e r a c t i o n between the e f f e c t of forage type and the method of processing on the devi a t i o n of CP and ADF MPL from the DM MPL of the processed forage (Table XIX). With the exception of the ADF MPL deviation from that of DM i n hammered OGH and OGL chopped at a TLC of 3.18 mm, a l l the deviations of CP or ADF MPL from that of DM within each processed forage were s i g n i f i c a n t l y d i f f e r e n t from zero. These deviations r e s u l t e d from the unequal d i s t r i b u t i o n of CP and/or ADF on the basis of p a r t i c l e length within each of the forages, as was discussed e a r l i e r . A negative deviation i n d i c a t e d that the nutrient -83- TABLE XIX: Deviation between the DM and CP, and DM and ADF median p a r t i c l e lengths (mm) of the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC). FORAGE NUTRIENT TLC ALF OGH OGL SEM# H -1.065 e -0.232 f -1.944 d C P . 3.18 -2.933 b c -0.280 f -3.392 a 0.119 6.35 -2.694c -0.279 f -3.471 a 9.53 -3.117 a b -0.283 f -3.328 a H 1.169 f -0.239 c * 0.116 e ADF 3.18 2.051 h -0.597 b -0.018 d e* 0.058 6.35 1.908Sh -0.858 a -0.098 c d 9.53 1.766S -0.934 a -0.150 c d Standard error of the mean f o r the values i n each n u t r i e n t row. Means with d i f f e r e n t superscripts within n u t r i e n t rows were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). Deviation between ADF and DM MPL not s i g n i f i c a n t l y d i f f e r e n t from zero (P > 0.05). was concentrated i n the shorter lengths of forage p a r t i c l e s whereas a p o s i t i v e d e v i a t i o n indicated that the nutri e n t was concentrated i n the longer p a r t i c l e s . A deviation that was not s i g n i f i c a n t l y d i f f e r e n t from zero i n d i c a t e d that the d i s t r i b u t i o n of the nu t r i e n t was s i m i l a r to that of the DM and that the nutri e n t was evenly d i s t r i b u t e d , by weight, throughout the various lengths of forage p a r t i c l e s . With a l l three forages, processing r e s u l t e d i n a concentration of CP i n the shorter lengths of p a r t i c l e s . The method of processing, however, d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) the deviation of CP MPL from DM MPL when OGH was processed. The CP MPL of ALF and OGL, on the other hand, deviated s i g n i f i c a n t l y l e s s (P < 0.05) from the DM MPL when the forages were hammered than i t d i d when the forages were chopped. The TLC used during chopping d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) the deviation of CP MPL from DM MPL i n -84- OGL whereas the deviation with ALF was greater (P < 0.05) at a TLC of 9.53 mm than i t was when the forage was chopped at the two shorter TLC. There was, however, no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n the deviation of CP from DM MPL between ALF chopped at a TLC of 3.18 mm and that chopped at a TLC of 6.35 mm. With the exception of ALF chopped at a TLC of 9.53 mm, there was a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) i n the deviation of CP MPL from DM MPL between the three forages within each method of processing. The deviation was the greatest with OGL, the smallest with OGH and intermediate with ALF. At a TLC of 9.53 mm, the difference i n the deviation of CP MPL from DM MPL between ALF and OGL was not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) . These deviations, however, were s i g n i f i c a n t l y greater (P < 0.05) than that found when OGH was chopped at a TLC of 9.53 mm. Processing had an inconsistent e f f e c t on the l o c a t i o n of ADF i n r e l a t i o n to p a r t i c l e length between the three forages. The deviations of ADF MPL from that of DM suggest that the ADF i n hammered OGL and a l l processed ALF was concentrated i n the longer lengths of p a r t i c l e s whereas the ADF i n chopped OGL and a l l processed OGH was somewhat concentrated i n the shorter p a r t i c l e lengths. The dev i a t i o n of ADF MPL from DM MPL i n ALF and OGH was s i g n i f i c a n t l y l e s s (P < 0.05) when the forages were hammered than i t was when they were chopped. With OGL, the deviation was p o s i t i v e when the forage was hammered and negative when i t was chopped. There was, however, no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n the deviation of ADF MPL from DM MPL between hammered OGL and OGL chopped at a TLC of 3.18 mm. There was a consistent trend towards a l e s s e r degree of ADF concentration i n the longer p a r t i c l e length f r a c t i o n s i n a l l three forages as the TLC used i n chopping increased. There was, however, no s i g n i f i c a n t -85- d i f f e r e n c e (P > 0.05) i n the deviation of ADF MPL from DM MPL between TLC i n chopped OGL; i n chopped ALF, the p o s i t i v e d e viation s i g n i f i c a n t l y decreased (P < 0.05) as TLC increased. The negative deviation of ADF MPL from DM MPL s i g n i f i c a n t l y increased (P < 0.05) when OGH was chopped at a TLC of 6.35 mm as compared with chopping at a TLC of 3.18 mm; there was, however, no s i g n i f i c a n t change (P > 0.05) i n the deviation when the TLC was increased from 6.35 to 9.53 mm. There was a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) i n the dev i a t i o n of ADF MPL from DM MPL between the three forages within each method of processing. The d e v i a t i o n was the lar g e s t , and p o s i t i v e , i n processed ALF, the smallest and close to zero i n processed OGL, and intermediate, but negative, i n processed OGH. The negative deviation of ADF MPL from that of DM i n OGH and OGL indicates an opposite r e l a t i o n s h i p between n u t r i e n t concentration and p a r t i c l e length to that found when p a r t i c l e length f r a c t i o n ADF content was regressed on the MPL of each f r a c t i o n (see Table XVII). The p o s i t i v e r e l a t i o n s h i p seen i n Table XVII would suggest that there should have been a p o s i t i v e d e v i a t i o n between the ADF and DM MPL i n the orchardgrass hays. There are two possible explanations f o r the f i n d i n g of a negative ADF deviation. Small f l u c t u a t i o n s occurred i n the ADF content of the p a r t i c l e length f r a c t i o n s such that some smaller length f r a c t i o n s had a higher ADF content than d i d some longer length f r a c t i o n s w i t h i n a given forage sample. I f the shorter length, higher ADF f r a c t i o n cumulatively contained more than 50% of the sample DM, which d i d occur, a negative d e v i a t i o n could r e s u l t when the cumulative ADF d i s t r i b u t i o n was calc u l a t e d . I t seems more probable, however, that, consistent with the r e s u l t s found i n Table XVII, there was no "actual" d i f f e r e n c e between the ADF and DM MPL within each of the -86- orchardgrass hays. The negative deviation that was found could simply have r e s u l t e d from differences i n the f i t t i n g of the Weibull function due to the cumulative e f f e c t of very small differences i n the ADF content of the d i f f e r e n t p a r t i c l e length f r a c t i o n s . In research i n v e s t i g a t i n g the e f f e c t of forage p a r t i c l e s i z e on forage u t i l i z a t i o n , the d i g e s t i b i l i t y of n u t r i t i o n a l components has always been r e l a t e d to the DM p a r t i c l e s i z e of the forage. However, the r e s u l t s of t h i s study ind i c a t e that the e f f e c t of the treatment combinations on the DM, CP and ADF MPL of forages processed by the same method was d i f f e r e n t depending on which n u t r i e n t was examined. Furthermore, the differences i n CP and ADF MPL between forages processed by the same method ranged from 0.2 to 3.3 mm and 0.6 to 5.2 mm r e s p e c t i v e l y . I t was also found that the d e v i a t i o n of CP or ADF MPL from that of DM within a given forage ranged from nearly zero to 3.5 mm. Some of these differences i n MPL, as with DM MPL were i n the range that has been shown to a f f e c t rate of passage from the rumen. D i f f e r e n t n u t r i e n t s w i t h i n a given processed forage may therefore have d i f f e r e n t rates of passage which may d i r e c t l y a f f e c t the ruminal d i g e s t i b i l i t y of the n u t r i e n t . Furthermore d i f f e r e n t forages with s i m i l a r DM MPL may have d i f f e r e n t CP or ADF MPL and vice-versa. Therefore, the d i g e s t i b i l i t y of a given n u t r i e n t component i n processed forage should be r e l a t e d to the median p a r t i c l e s i z e of that nut r i e n t to avoid the introduction of uncontrolled experimental error from r e l a t i n g CP or ADF d i g e s t i b i l i t y to DM median p a r t i c l e s i z e . C o e f f i c i e n t s of Spread The CS of a p a r t i c l e length d i s t r i b u t i o n (see Chapter 1) i s a measure of the r e l a t i v e d i s p e r s i o n of p a r t i c l e s lengths around the MPL. I t i s possible -87- f o r two samples of processed forage to have the same MPL but have d i f f e r e n t CS. As the value of the CS increases from 0 to 3.212, the r e l a t i v e d i s p e r s i o n of p a r t i c l e lengths decreases and the p a r t i c l e length d i s t r i b u t i o n becomes less skewed to the r i g h t (see Chapter 1). As with MPL, there was a s i g n i f i c a n t i n t e r a c t i o n between the e f f e c t of forage type and method of processing on the DM, CP and ADF CS of the p a r t i c l e length d i s t r i b u t i o n s that were produced during processing (Table XX). The s i g n i f i c a n t differences between the CS of the various treatment combinations suggest that the nature of the p a r t i c l e length d i s t r i b u t i o n (eg. normal vs. lognormal) that i s produced by d i f f e r e n t processing methods with d i f f e r e n t forages i s not constant. These differences i n the nature of the p a r t i c l e length d i s t r i b u t i o n may p a r t i a l l y explain the observed lack of TABLE XX: DM, CP and ADF c o e f f i c i e n t s of spread of the forages hammered through a 12.7 mm screen (H) and chopped at three t h e o r e t i c a l lengths of cut (TLC). FORAGE NUTRIENT TLC ALF OGH OGL SEM # H 1. ,020 a b 0, ,954a 1, ,301c DM 3. 18 1. ,088 a b 1. .087 a b 1, .142b 0 .043 6. 35 1. ,138b 1. ,344c 1, ,275c 9. 53 1. .276c 1, ,384° 1, .524d H 0. .899a 0. .935 a b 1. ,066 b c d CP 3. 18 1. 0 8 9 c d 1, .121 c d 1. 0 2 0 a b c 0 .043 6. 35 1. ,093 c d 1. ,337e 1. .194d 9. 53 1. ,183 d 1, ,424e 1, ,417e H 1, ,157 b c 0. ,959a 1, ,337 d ADF 3. 18 1, .137 b c 1, . 0 4 7 a b 1, ,138 b c 0 .047 6. 35 1. ,241 c d 1, 2 8 8 c d 1, ,313 d 9. 53 1 .375 d 1, .368 d 1 .572e Standard error of the mean for the values i n each nut r i e n t row. e Means with d i f f e r n t superscripts within n u t r i e n t rows were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -88- f i t when some p a r t i c l e s i z e d i s t r i b u t i o n s have been f i t t e d to the lognormal d i s t r i b u t i o n (see Chapterl). D i f f e r e n t forages that had the same MPL when processed by the same method d i d not always have s i m i l a r CS. ALF and OGL had s i m i l a r D.M MPL when the forages were chopped at a TLC of 6.35 mm and s i m i l a r ADF MPL when the forages were chopped at a TLC of 9.53 mm. In both of these cases, however, the CS of OGL was s i g n i f i c a n t l y greater (P < 0.05) than that of ALF. The CP MPL of OGH and OGL were s i m i l a r when the forages were chopped at a TLC of 6.53 mm whereas the CS of OGH was s i g n i f i c a n t l y greater (P < 0.05) than that of OGL. When ALF and OGH were hammered, s i m i l a r ADF MPL were produced, but the CS of ALF was s i g n i f i c a n t l y greater (P < 0.05) than that of OGL. Therefore, even i f s i m i l a r MPL are produced i n d i f f e r e n t forages processed by the same method, the p a r t i c l e length d i s t r i b u t i o n s of the processed forages may not be s i m i l a r . On the other hand, i n every case where d i f f e r e n t processing methods used on the same forage produced s i m i l a r MPL, the CS of the processed forage were also not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05). When each of the forages was chopped, a s i g n i f i c a n t increase i n the DM, CP or ADF MPL was accompanied by a s i g n i f i c a n t increase (P < 0.05) i n the CS. Between forages processed by the same method there was no consistent r e l a t i o n s h i p between a difference i n MPL and a dif f e r e n c e i n CS. For example, there was no s i g n i f i c a n t difference i n the ADF CS of the three forages when they were chopped at a TLC of 3.18 or 6.35 mm. At the same TLC, the ADF MPL of OGH was s i g n i f i c a n t l y smaller (P < 0.05) than those of ALF and OGL which were not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) from each other. Conversely, there was no s i g n i f i c a n t d i f f e r e n c e i n both CP MPL and CP CS between the three forages when they were chopped at a TLC of 3.18 mm. -89- F i n a l l y , there were also cases where d i f f e r e n t forages processed by d i f f e r e n t methods had s i m i l a r MPL but had d i f f e r e n t CS. For example, the DM MPL of hammered OGL was not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05) from that of OGH chopped at a TLC of 3.18 mm, whereas the DM CS of the OGL was s i g n i f i c a n t l y smaller (P < 0.05) than that of the OGH. The opposite was also evident i n that d i f f e r e n t forages processed by d i f f e r e n t methods had d i f f e r e n t MPL but had s i m i l a r CS. The ADF MPL of OGL chopped at a TLC of 3.18 mm was s i g n i f i c a n t l y l a rger (P < 0.05) than that of hammered ALF whereas the CS for the two processed forages were not s i g n i f i c a n t l y d i f f e r e n t (P > 0.05). The differences i n the e f f e c t of treatment combination on the DM, CP and ADF CS, and the deviation of CP and ADF CS from the DM CS were not analyzed due to the confounding e f f e c t s of the associated changes i n DM, CP and ADF MPL. For the p a r t i c l e length d i s t r i b u t i o n s of a given forage, the length at which 100 % cumulative weight undersize occurs, i s the same f o r a l l three n u t r i e n t d i s t r i b u t i o n s ( i e ; the length of the longest p a r t i c l e i n the sample). Because each d i s t r i b u t i o n has the same endpoint, a decrease i n the MPL of a nut r i e n t , due to a higher concentration of the nu t r i e n t i n the shorter lengths of p a r t i c l e s , w i l l r e s u l t i n a smaller CS f o r that nutrient as compared with the DM CS. Conversely, an increase i n the MPL of a nut r i e n t , due to a higher concentration of the nu t r i e n t i n the longer lengths of p a r t i c l e s , w i l l r e s u l t i n a increased CS f o r that n u t r i e n t as compared with the DM CS. Therefore, differences i n the e f f e c t of forage and method of processing on nu t r i e n t CS, and the deviation of nu t r i e n t CS from the DM CS, are a function of the difference between the DM and nutri e n t MPL of each processed forage. Although i t i s recognized that the median p a r t i c l e s i z e of processed -90- forage can have a d i r e c t e f f e c t on the u t i l i z a t i o n of forages fed to ruminants, i t i s s t i l l unclear as to what e f f e c t the d i s t r i b u t i o n of p a r t i c l e sizes around the median has on forage u t i l i z a t i o n . Moseley (1984) found that DM intake, disappearance of d i g e s t i b l e organic matter from the rumen and dry matter flow i n the abomasum were more c o n s i s t e n t l y c o r r e l a t e d with the proportion of forage p a r t i c l e s passing a 1 mm sieve plus that of soluble dry matter than they were with the geometric mean diameter of the forage. Therefore, differences between forages i n the d i s t r i b u t i o n of p a r t i c l e s i z e s around a common median p a r t i c l e s i z e may have an e f f e c t on forage u t i l i z a t i o n . The r e s u l t s of t h i s study have shown that f or DM, CP and ADF, the CS of d i f f e r e n t forages processed by the same method may not be s i m i l a r . Furthermore, d i f f e r e n t processed forages that have s i m i l a r MPL may not n e c e s s a r i l y have s i m i l a r CS. Therefore, i n the preparation of dietary treatments of processed forage, f a i l u r e to equalize or otherwise c o n t r o l the differences i n CS between treatments, may, as could differences i n MPL, introduce uncontrolled experimental error into the r e s u l t s of research i n which processed forage i s fed. -91- SUMMARY T h e s t u d y r e p o r t e d i n t h i s c h a p t e r w a s u n d e r t a k e n t o d e t e r m i n e i f s i m i l a r DM, C P a n d A D F p a r t i c l e l e n g t h d i s t r i b u t i o n s w e r e p r o d u c e d w h e n d i f f e r e n t f o r a g e s w e r e p r o c e s s e d b y t h e s a m e m e t h o d . A l f a l f a a n d h i g h q u a l i t y a n d l o w q u a l i t y o r c h a r d g r a s s h a y w e r e h a m m e r e d t h r o u g h a 1 2 . 7 mm s c r e e n a n d c h o p p e d a t 3 t h e o r e t i c a l l e n g t h s o f c u t ( T L C : 3 . 1 8 , 6 . 3 5 a n d 9 . 5 3 mm) . T h e e f f e c t o f f o r a g e t y p e a n d m e t h o d o f p r o c e s s i n g o n t h e p a r t i c l e l e n g t h d i s t r i b u t i o n o f t h e p r o c e s s e d f o r a g e w a s d e t e r m i n e d b y c o m p a r i n g t h e DM, CP a n d A D F m e d i a n p a r t i c l e l e n g t h s ( M P L ) a n d c o e f f i c i e n t s o f s p r e a d ( C S ) o f t h e p a r t i c l e l e n g t h d i s t r i b u t i o n s t h a t w e r e p r o d u c e d . D i f f e r e n t f o r a g e s t h a t w e r e p r o c e s s e d u s i n g t h e s a m e m e t h o d d i d n o t a l w a y s r e s u l t i n t h e p r o d u c t i o n o f s i m i l a r DM, CP o r A D F M P L , o r s i m i l a r C S . F u r t h e r m o r e , p r o c e s s e d f o r a g e s t h a t d i d h a v e s i m i l a r DM M P L , o r s i m i l a r C S , d i d n o t a l w a y s h a v e s i m i l a r CP a n d / o r A D F M P L , o r s i m i l a r C S . T h e r e w e r e a l s o s i g n i f i c a n t d i f f e r e n c e s b e t w e e n t h e M P L o f d i f f e r e n t n u t r i e n t s w i t h i n a g i v e n f o r a g e . T h e s e d i f f e r e n c e s b e t w e e n t h e M P L o f d i f f e r e n t f o r a g e s t h a t w e r e p r o c e s s e d b y t h e s a m e m e t h o d , a n d o f d i f f e r e n t n u t r i e n t s w i t h i n a g i v e n f o r a g e , w e r e o f a m a g n i t u d e t h a t h a s b e e n s h o w n t o s i g n i f i c a n t l y a f f e c t c h e w i n g b e h a v i o r , r a t e o f p a s s a g e a n d d i g e s t i b i l i t y o f some f o r a g e s w h e n f e d t o r u m i n a n t s . - 9 2 - CHAPTER I I I THE EFFECT OF FORAGE PARTICLE LENGTH AND FORAGE TO CONCENTRATE RATIO ON INTAKE AND CHEWING BEHAVIOR IN DAIRY CATTLE INTRODUCTION Voluntary feed intake by ruminants i s l i m i t e d by the rate of d i g e s t i o n and the rate of passage of undigested feed p a r t i c l e s from the rumen. The passage of the p a r t i c l e s i s i n turn l i m i t e d to those p a r t i c l e s that have been s u f f i c i e n t l y reduced i n s i z e , by mastication during eating and rumination, to a s i z e that i s capable of passing through the reticulo-omasal o r i f i c e . Research has shown, however, that the reduction of the p a r t i c l e s i z e i n f eedstuffs fed to ruminants ( e s p e c i a l l y forages) decreases the time required f o r p a r t i c l e s i z e reduction by chewing (Santini et a l . . 1983) and increases the rate of passage of digesta from the rumen (Rode et a l . . 1985). The p a r t i c l e s i z e of a feedstuff, over and above the chemical f i b e r content of the feed, i s also important i n providing p h y s i c a l stimulation of normal rumen function. Excessive reduction of p a r t i c l e s i z e has been shown to adversely a f f e c t intake by decreasing rate of passage, to reduce f a t l e v e l s i n the milk of l a c t a t i n g dairy cows by a l t e r i n g rumen fermentation, and to promote n u t r i t i o n a l disorders such as r u m i n i t i s , displaced abomasum and l i v e r abscess. The excessive reduction of p a r t i c l e s i z e i s characterized by an almost complete cessation of rumination a c t i v i t y . Unfortunately, much of the research on the e f f e c t s of p a r t i c l e s i z e on ruminant d i g e s t i o n and forage u t i l i z a t i o n has not involved the q u a n t i f i c a t i o n of p a r t i c l e s i z e i n the feedstuffs that were fed. I d e n t i f i c a t i o n of the quantitative r e l a t i o n s h i p between fe e d s t u f f p a r t i c l e -93- s i z e and parameters of ruminant di g e s t i o n i s required f o r the maximization of f e e d s t u f f u t i l i z a t i o n and the prevention of n u t r i t i o n a l disorders. The monitoring of chewing behavior i s one of the simplest methods for determining the e f f e c t of p a r t i c l e s i z e on ruminant digestion. Therefore, using the method described i n Chapter 1 for the q u a n t i f i c a t i o n of forage p a r t i c l e length, the objectives of the following study were to: 1. determine the e f f e c t of forage p a r t i c l e length on the chewing behavior of l a c t a t i n g dairy cows when an orchargrass hay, chopped to two d i f f e r e n t median p a r t i c l e lengths, was fed at two forage to concentrate r a t i o s . 2. determine the r e l a t i o n s h i p between forage p a r t i c l e length and chewing behavior i n dairy steers fed a timothy-brome hay chopped to four d i f f e r e n t median p a r t i c l e lengths. -94- LITERATURE REVIEW DIGESTION AND PASSAGE OF FEED PARTICLES IN THE RUMEN The disappearance of fee d s t u f f from the rumen can be described by the processes of digestion, absorption and removal by passage through the reticulo-omasal o r i f i c e . The microbial d i g e s t i o n of f e e d s t u f f i n the rumen i s accomplished by microbial attachment to and chemical degradation of the feed p a r t i c l e s i n the r a t i o n . However, not a l l components of feedstuffs are degradable by microbial digestion. Researchers using i n v i t r o and i n s i t u techniques have demonstrated that there e x i s t s a " p o t e n t i a l l y d i g e s t i b l e " f r a c t i o n which i s l i m i t e d i n s i z e by the s i z e and composition of the c e l l w a ll f r a c t ion (Robles et a l . . 1980). The p o t e n t i a l l y d i g e s t i b l e f r a c t i o n of f e e d s t u f f s generally consists of 90 to 100 % of the c e l l content f r a c t i o n , plus varying proportions of the c e l l w all f r a c t i o n . Part of the p o t e n t i a l l y d i g e s t i b l e f r a c t i o n includes a rumen f l u i d soluble f r a c t i o n which does not require microbial degradation to leave the rumen. Products of s o l u b l i z a t i o n and m i c r o b i a l d i g e s t i o n are e i t h e r absorbed through the rumen wall, expelled as gases by e r u c t a t i o n or passed from the rumen through the reticulo-omasal o r i f i c e as part of the f l u i d f r a c t i o n of the digesta, or as microbial c e l l s attached to feed p a r t i c l e s . In t o t a l , disappearance of fee d s t u f f from the rumen due to s o l u b l i z a t i o n and microbial d i g e s t i o n can range up to about 70 % under p r a c t i c a l feeding conditions. The undigested or i n d i g e s t i b l e f r a c t i o n of ingested feed i s removed from the rumen by passage through the reticulo-omasal o r i f i c e . Such passage, however, i s l i m i t e d by the s i z e of the p a r t i c l e s . Uden and Van Soest (1982) demonstrated that r e t e n t i o n time of chromium mordanted f i b e r p a r t i c l e s i n -95- the rumen increased with increasing p a r t i c l e s i z e . Poppi et a l . (1980) showed that when p a r t i c l e s of digesta attempted to leave the rumen there was an increasing resistance to passage as the s i z e of the p a r t i c l e s increase. These researchers found an i n f l e c t i o n point i n p a r t i c l e s i z e "resistance" to passage curves equivalent to a sieve s i z e of 1.18 mm for sheep. This means that p a r t i c l e s capable of passing through a 1.18 mm sieve have a higher p r o b a b i l i t y of passage than do p a r t i c l e s that w i l l be retained on a 1.18 mm sieve. They therefore concluded that there existed a c r i t i c a l p a r t i c l e s i z e above which passage may be possible, but that the p r o b a b i l i t y f o r passage was low. Smith et a l . (1983) also supported the 1.18 mm sieve s i z e as being c r i t i c a l f o r passage i n sheep since, i n t h e i r work, only 0.2% of p a r t i c l e s passing to the doudenum would have been retained on a sieve of that s i z e . The researchers also showed that p a r t i c l e s of natural l o g a r i t h i m mean size 5.3 (.2mm) passed from the rumen without being reduced i n s i z e . Their work, however, was only based on r e s u l t s from one animal. Welch and Smith (1978) measured the passage of four lengths of polypropylene ribbon (0.5, 1.0, 1.5 and 2.0 mm) from the rumen i n c a t t l e and three lengths i n sheep (0.25, 0.5 and 1.0 mm). The recovery of unchewed p a r t i c l e s i n the feces was inversely proportional to the length of the p a r t i c l e s . The researchers also found, i n both species of animals, that the longest lengths would pass from the rumen unchewed. This length f r a c t i o n , however, only amounted to about 1.0% of those p a r t i c l e s placed i n the rumen. The passage of undigested feed residues from the rumen i s f a c i l i t a t e d by the reduction of p a r t i c l e s i z e by m i c r o b i al degradation, chewing during eating and ruminating and d e t r i t i o n from reticulo-rumen m o t i l i t y (Reid et a l . . 1977). Once p a r t i c l e s pass from the rumen, there appears to be no fu r t h e r reduction i n p a r t i c l e s i z e (Poppi et a l . . 1980; Smith et a l . . 1983). -96- REDUCTION OF FEEDSTUFF PARTICLE SIZE IN THE RUMEN Microbial Degradation and Detrition in the Rumen M i c r o b i a l d i g e s t i o n has been shown to have a d i r e c t e f f e c t on the reduction of p a r t i c l e s i z e of feedstuffs and an i n d i r e c t e f f e c t by increasing the ' b r i t t l e n e s s ' of digesta feed p a r t i c l e s . Murphy and N i c o l l e t i (1984) incubated coarsely ground a l f a l f a hay i n v i t r o f o r 48 hrs and found that although the median p a r t i c l e s i z e d i d not change, the log^Q standard deviation of the p a r t i c l e s i z e d i s t r i b u t i o n increased l i n e a r l y with time of incubation. This would indicate a uniform chemical degradation of a l l p a r t i c l e s i z e s . When the same hay was incubated i n s i t u , there was a 19% reduction i n mean p a r t i c l e s i z e a f t e r 96 hours of incubation with no change i n standard deviation. Welch (1982) incubated 2 cm a l f a l f a and f i r s t and second cut grass hay stems i n s i t u f o r ten days and observed no apparent change i n the p h y s i c a l appearance of the stems other than an increase i n the b r i t t l e n e s s of the p a r t i c l e s . This increase i n b r i t t l e n e s s may have been responsible f o r the reduction of p a r t i c l e s i z e seen i n s i t u by Murphy and N i c o l l e t (1984) by making the p a r t i c l e s more susceptible to d e t r i t i o n from rumen movement. Unfortunately, no research has as yet been attempted to quantify the e f f e c t of rumen movement on comminution of ingested f e e d s t u f f s . Although i t has been demonstrated that microbial degradation and d e t r i t i o n from rumen movement contributes d i r e c t l y to p a r t i c l e s i z e reduction i n the rumen, i t i s more l i k e l y that the increase i n b r i t t l e n e s s from microbial d i g e s t i o n increases the effectiveness of p a r t i c l e s i z e reduction by chewing during rumination. -97- Chewing Behavior Chewing during eating and rumination i s the primary mechanism for the reduction of p a r t i c l e s i z e of undigested and i n d i g e s t i b l e feed residues i n the rumen to a s i z e capable of passing through the reticulo-omasal o r i f i c e . The process of chewing during eating involves prehension, mastication, s a l i v a t i o n and swallowing. Mastication during eating serves a t r i p l e purpose. F i r s t l y , mastication i s required f o r the reduction of p a r t i c l e size which, along with s a l i v a t i o n , permits food to be swallowed. Secondly, the reduction i n p a r t i c l e s i z e increases the surface area of the ingested p a r t i c l e s which enhances microbial attachment and the rate of d i g e s t i o n i n the rumen. The s a l i v a t i o n which takes place during eating i s also important f o r the maintenance of rumen pH which has a d i r e c t e f f e c t on the rate of m i c r o b i a l d i g e s t i o n and reticulo-rumen m o t i l i t y . F i n a l l y , the reduction of p a r t i c l e s i z e during eating increases the p r o b a b i l i t y of d i r e c t passage of newly ingested p a r t i c l e s from the rumen. Considerable reduction i n p a r t i c l e s i z e i s accomplished by chewing during eating. Reid et a l . (1979) fed wethers chaffed a l f a l f a i n which 97% (w/w) DM of the p a r t i c l e s o f f e r e d to the animals were too large to pass through a 1 mm screen. A f t e r chewing during eating, 52% of the p a r t i c l e s passed through the same screen. Lee and Pearce (1984) found that chewing during eating i n steers reduced the proportion of p a r t i c l e s retained on a 1 mm screen by 30 to 40 percent. In terms of Modulus of Fineness, p a r t i c l e s i z e of ingested feed was reduced by 46 to 52 percent. There i s , however, a great v a r i a t i o n i n the extent to which animals reduce p a r t i c l e s i z e during eating (Lee and Pearce, 1984; G i l l et a l , 1966). I t appears that the extent of comminution required during eating may be l i m i t e d to that required for bolus formation and l u b r i c a t i o n p r i o r to -98- swallowing. Welch and Smith (1978) found that 99% of one centimeter long p a r t i c l e s of polypropylene ribbon were recovered unchewed i n the rumen of a f i s t u l a t e d steer fed a mixture of the ribbon and concentrates. Balch (1958) found that the rate of feed ingestion, weight of s a l i v a produced and rate of s a l i v a t i o n during eating were not consistent with a l l types of fee d s t u f f s . Hay, which had a l a r g e r p a r t i c l e s i z e and a higher l e v e l of f i b e r , was consumed at a f a s t e r rate than was concentrate. Swallowed boluses of hay contained 12-16% dry matter whereas those of coarsely ground concentrates contained 35-40% dry matter. Calculations revealed that 3-4 times the amount of s a l i v a was secreted per u n i t weight of hay consumed as compared with concentrates. On the other hand, the rate of s a l i v a s e c r e t i o n was approximately doubled when the animals were fed concentrates. The differences i n bolus dry matter content was caused by a more r a p i d ingestion rate of the concentrates as compared with that of hay. Therefore, i n i t i a l p a r t i c l e s i z e and resistance to p a r t i c l e s i z e reduction may have a r e g u l a t i n g e f f e c t on eating rate. Although, the amount of comminution occurring during eating may be l i m i t e d to that required to enable swallowing, the reduction of p a r t i c l e s i z e during eating d i r e c t l y enhances the passage of p a r t i c l e s from the rumen. B a i l y and Balch (1961) studied the e f f e c t of chewing during eating on the removal of p a r t i c u l a t e matter from the rumen by comparing the rumination times of a cow fed hay normally, or by placement of hay d i r e c t l y into the rumen through a f i s t u l a . Time spent ruminating was increased by close to 50% with " f i s t u l a feeding". These r e s u l t s were supported by Bae et a l . (1981) who found that decreased time spent eating per kg of c e l l w all intake was associated with increased time spent ruminating. P a r t i c l e s i z e reduction and s a l i v a t i o n from chewing during rumination, -99- as with eating, i s important f o r enhancing microbial digestion. However, chewing during rumination i s the f i n a l and most important mechanism f o r the reduction of p a r t i c l e s i z e enabling passage from the rumen through the reticulo-omasal o r i f i c e . The e s s e n t i a l i t y of rumination f o r the passage of undigested p a r t i c l e s has been c l a s s i c a l l y demonstrated by the prevention of rumination by muzzling i n sheep. Pearce and Moir (1964) found that prevention of rumination increased r e t e n t i o n times and subsequently increased DM, OM and crude f i b e r apparent d i g e s t i b i l i t i e s . However, muzzling d i d not completely i n h i b i t p a r t i c u l a t e passage from the rumen, which lead the researchers to conclude that microbial d i g e s t i o n must account for a s u b s t a n t i a l degree of p a r t i c l e s i z e reduction. Unfortunately, complete prevention of rumination was not accomplished by the muzzles which meant that the e f f e c t of the prevention of rumination may have been underestimated. Welch (1982) accomplished complete prevention of rumination using steers. At each feeding, the animals had access to hay f o r 2 hours a f t e r which they were muzzled u n t i l the next feeding period. Intake of hay was markedly reduced by muzzling. Towards the end of the feeding periods, the muzzled animals pr e f e r r e d to ruminate rather than eat. In another t r i a l , the researcher had animals die of esophageal and pharynx impaction when the animals attempted to ruminate while muzzled. Therefore, factors that a f f e c t the disappearance of f e e d s t u f f from the rumen, e i t h e r by a f f e c t i n g d i g e s t i b i l i t y or rate of passage through the reticulo-omasal o r i f i c e , also a f f e c t the chewing behavior of the animal. For t h i s reason, Balch (1971) proposed the use of the t o t a l time spent chewing (eating plus rumination) as an index of the fibrousness of feedstuffs fed to ruminants. -100- FACTORS AFFECTING CHEWING BEHAVIOR Feedstuff P a r t i c l e Size The reduction of p a r t i c l e s i z e i n feedstuffs fed to ruminants has an e f f e c t on the rate of feed ingestion, rate and extent of microbial digestion, chewing behavior and rate of passage of digesta p a r t i c l e s from the rumen. A change i n the rate of passage of p a r t i c l e s from the rumen i n turn has an e f f e c t on the s i t e of f e e d s t u f f d i g e s t i o n i n the g a s t r o - i n t e s t i n a l t r a c t . I t i s well documented that the reduction of p a r t i c l e s i z e of feedstuffs can be associated with an increase i n voluntary intake (Weston and Kennedy, 1984). This e f f e c t , however, has been shown not to be consistent for a l l species and maturities of forage. For example, Campling et a l . (1963) and Campling and Freer (1966) found that coarse grinding of an a r t i f i c i a l l y d r i e d grass hay or a medium q u a l i t y ryegrass hay d i d not s i g n i f i c a n t l y a f f e c t intake. However, Campling and Freer (1966) found that grinding and p e l l e t i n g oat straw increased intake by 26% compared with feeding i n the long form. Lee and Pearce (1984) found s i g n i f i c a n t c o r r e l a t i o n s between the intake of some feeds and the modulus of fineness and percent of p a r t i c l e s retained on a 1 mm screen. This c o r r e l a t i o n , however, was not s i g n i f i c a n t f o r a l l feeds tested. In general, the e f f e c t of p a r t i c l e s i z e reduction on increasing intake appears to have l i t t l e e f f e c t with high q u a l i t y forages and concentrates and an increasing e f f e c t when the fibrousness of the feed increases (Weston and Kennedy, 1984). The reduction of p a r t i c l e s i z e of forages fed to ruminants appears to exert i t s greatest e f f e c t by increasing the rate of passage of digesta p a r t i c l e s from the rumen. Campling and Freer (1966) found that grinding of -101- ryegrass hay d i d not s i g n i f i c a n t l y increase voluntary feed intake but s i g n i f i c a n t l y decreased the retention time of stained p a r t i c l e s i n the rumen. The reduction i n r e t e n t i o n time was also associated with a considerable reduction i n the extent of digestion. In the same study, grinding of oat straw also s i g n i f i c a n t l y reduced the r e t e n t i o n time of p a r t i c l e s i n the rumen and the d i g e s t i b i l i t y of the forage. The reduction i n d i g e s t i b i l i t y was, however, not as pronounced as with the hay d i e t . This d i f f e r e n c e may have been due to the smaller siz e of the p o t e n t i a l l y d i g e s t i b l e f r a c t i o n that i s normally found i n straws as compared with that found i n grass hays. The e f f e c t of feedst u f f p a r t i c l e s i z e on the process of d i g e s t i o n i n ruminants has been shown to be r e f l e c t e d i n the chewing behavior of the animals. As e a r l y as 1935, Kick and Gerlaugh (1935) showed that reducing the p a r t i c l e s i z e of good q u a l i t y a l f a l f a hay by chopping and grinding reduced the amount of time steers spent eating and ruminating and was associated with a decreased r e t e n t i o n time of digesta i n the rumen. This e f f e c t , however, was not consistent over a l l treatments. There was no s i g n i f i c a n t d i f f e r e n c e i n the amount of time spent chewing between a hay fed i n the long form and that chopped to an estimated median length of 24.7 mm. The amount of time spent chewing declined when the forage was chopped to approximately 6.4 mm i n length and then declined further when the forage was ground. The feeding of ground hay also caused a marked amount of pseudo-rumination which in d i c a t e d that the forage had l o s t i t s a b i l i t y to stimulate normal rumination a c t i v i t y . Since the work of Kick and Gerlaugh (1935), the majority of the research on the e f f e c t of p a r t i c l e s i z e on chewing behavior has predominantly used q u a l i t a t i v e treatments inv o l v i n g the feeding of forage i n the long, coarsely -102- chopped and ground form or j u s t the long and ground forms. The r e s u l t s of t h i s research have i n general supported the research of Kick and Gerlaugh (1935) i n that there appears to be no s i g n i f i c a n t reduction i n the amount of time spent chewing when forage i s coarsely chopped as compared with feeding i n the long form (eg. Kick et a l . . 1937; Gordon, 1958 ) and that grinding s i g n i f i c a n t l y reduces both the amount of time spent eating and ruminating (Kick et a l . . 1937; Balch, 1952; Gordon, 1958; Freer and Campling, 1965; Campling and Freer, 1966).In many cases the f i n e grinding of forages has l e d to an almost complete ceassation of normal rumination a c t i v i t y and a marked occurrence of pseudo-rumination. Therefore, the p a r t i c l e s i z e of feedstuffs i s important i n stimulating normal rumination a c t i v i t y . The need for p h y s i c a l stimulation of the rumen wall by digesta p a r t i c l e s i n promoting normal rumination has been c l a s s i c a l l y demonstrated. Balch (1952) restored normal rumination a c t i v i t y i n a cow fed ground hay by p l a c i n g a b r i s t l e brush i n the reticulum of the animal. Welch (1982) found a large reduction i n normal rumination a c t i v i t y when l a c t a t i n g cows were fed a l f a l f a meal p e l l e t s and concentrates. Normal rumination a c t i v i t y was restored when 200 grams of polypropylene ribbon was introduced into the d i e t . Balch (1952) found that although grinding of forage d i d not always i n h i b i t the t r i p l e contraction of the reticulum seen during normal rumination, the lack of p h y s i c a l stimulus of the rumen wall caused by grinding i n h i b i t e d the r e g u r g i t a t i o n r e f l e x required for normal rumination. The same lack of stimulus has also been seen when die t s predominantly comprised of concentrates have been fed. (Freer and Campling, 1965). -103- Level of Intake As discussed above, most feedstuffs contain a f r a c t i o n that i s not p o t e n t i a l l y d i g e s t i b l e i n the rumen. Therefore, as intake increases, the amount of i n d i g e s t i b l e material that must be cleared from the rumen also increases. Subsequently, increased intake r e s u l t s i n an increase i n time animals spend eating and ruminating. The r e l a t i o n s h i p between intake and time spent eating and ruminating, however, i s not constant. Welch and Smith (1969b) studied the e f f e c t of increasing hay intake on the rumination time i n sheep previously fasted f o r 48 hours. A 100% increase i n hay intake, from 500 to 1000 grams fed as a s i n g l e meal, increased the time the animals spent ruminating by only 67%. Increasing s i n g l e meal intake from 250 to 1000 grams i n 250 gram i n t e r v a l s gave a s t a t i s t i c a l l y s i g n i f i c a n t l i n e a r increase i n rumination time. However, the incremental increase between the 750 and 1000 gram intakes was about one h a l f the d i f f e r e n c e between the lower intake l e v e l s . When the increments between intake l e v e l s remained the same but intakes ranged from 250 grams to a maximum of 1800 grams per day, and the animals were fed continuously, there was a non-linear increase i n rumination time with increased intake; the amount of rumination per kg of intake subsequently decreased as intake increased. Bae et a l . (1981) also found that rumination time per kg intake decreased with increasing l e v e l of intake when dry H o l s t e i n cows were fed hay at 50, 75, 100, and 125 % of d a i l y NRC recommended dry matter intake and r e s u l t s were expressed as chewing time per kg of c e l l w all intake. However, at the higher l e v e l s of intake the cows s i g n i f i c a n t l y increased t h e i r chewing rate during rumination which may have compensated f o r the reduction i n time spent ruminating. The researchers also found that eating time per kg of c e l l w all intake increased with increasing intake. Subsequently the t o t a l -104- time chewing per kg c e l l w all intake d i d not d i f f e r s i g n i f i c a n t l y with l e v e l of intake. Bae et a l . (1981) concluded that t h e i r r e s u l t s i n d i c a t e d that ingested roughages required a constant amount of comminution by the combined a c t i o n of eating and rumination. The increase i n time spent chewing during eating, per kg of intake, with increased l e v e l s of intake may be due to a decrease i n intake and an increase i n chewing a c t i v i t y per bolus swallowed towards the end of a meal. G i l l et a l . (1966) studied the eating behavior and p a r t i c l e s i z e of swallowed hay i n dairy c a t t l e fed at two l e v e l s of intake. As intake increased from 5 to 7.5 kg per day, there was an increase i n the time spent eating from 15.4 to 18.3 min per kg of intake. Increasing the amount of feed o f f e r e d per meal d i d not s i g n i f i c a n t l y a f f e c t the chewing rate per minute but increased the number of chews per bolus swallowed. The researchers also found that with both l e v e l s of intake, the number of chews per bolus increased and the rate of bolus swallowing decreased as the meal progressed. G i l l et a l . (1966) also found that a higher number of chews per bolus swallowed during eating was associated with a reduced mean p a r t i c l e s i z e i n the swallowed boluses. Therefore, increasing the l e v e l of intake increases the amount of time required to consume the feed while the increased number of chews per bolus swallowed and decreased rate of swallowing as a meal progresses causes an increase i n eating time per kg of intake. However, the greater reduction i n p a r t i c l e s i z e associated with increased time spent eating r e s u l t s i n a decreased requirement f o r time spent ruminating per kg of intake as the l e v e l of intake increases. Due to the e f f e c t s of changes i n intake l e v e l on chewing behavior described above, r e s u l t s from experiments, where intake l e v e l s between animals are not equal, must be analyzed on the basis of the -105- t o t a l amount of chewing a c t i v i t y that occurs per kg of intake. Chemical Composition of Feedstuff The amount of time animals spend ruminating i s r e l a t e d to the amount of undigested feed residue i n the rumen. Welch and Smith (1968) found that immediately a f t e r the removal of feed from sheep being fasted there was a rap i d decline i n rumination a c t i v i t y which f e l l to zero a f t e r 36 hours. Examination of rumen contents of a s a c r i f i c e d sheep showed that the rumen contents contained i n s u f f i c i e n t fibrous constituents required f o r stimul a t i o n of rumination. Upon refeeding, normal rumination commenced wi t h i n 24 hours. Therefore any fa c t o r d i r e c t l y a f f e c t i n g the d i g e s t i b i l i t y of f e e d s t u f f s i n the rumen w i l l have a d i r e c t e f f e c t on the amount of time spent ruminating. The chemical composition and the s i z e of the p o t e n t i a l l y d i g e s t i b l e f r a c t i o n of feedstuffs has been shown to be the most important f a c t o r determining the rate of digesta disappearance from the rumen (Fonnesbeck et a l . . 1981). Since the c e l l contents of feedstuff approach 100% d i g e s t i b i l i t y (Fonnesbeck et a l . . 1981), the s i z e and composition of the f i b e r f r a c t i o n appear to c o n t r o l the l e v e l of undigested residues i n the rumen and, therefore, has an e f f e c t on the amount of time an animal spends ruminating. Robles et a l . (1981) fed mature wethers orchardgrass hay which v a r i e d i n c e l l w a l l content from 60 to 78 percent. These researchers found that as c e l l w all concentration increased, DM and DE intake, and DM d i g e s t i b i l i t y and excretion rate decreased while c e l l w all intake, rumen volume and rumen c e l l w a l l content and re t e n t i o n time increased s i g n i f i c a n t l y . They also found that on d i f f e r e n t d i e t s , the animals ate to a constant i n d i g e s t i b l e c e l l w all intake. An increase i n c e l l w all intake and increased retention -106- time with feedstuffs of increasing c e l l w all content has been shown to increase amount of time spent ruminating. Welch and Smith (1969a) fed sheep early-cut orchardgrass hay, l a t e cut mixed grass hay, weedy oat straw, 2nd cut mixed a l f a l f a grass hay, and oat straw containing 22.8, 8.0, 7.3, 17.8 and 5.4 percent crude p r o t e i n and 27.1, 36.4, 39.2, 28.3, and 42.9 percent crude f i b e r r e s p e c t i v e l y . They found that the simple c o r r e l a t i o n between rumination time and forage c e l l w all intake was 0.99 whereas the simple c o r r e l a t i o n between rumination time and crude p r o t e i n intake was only 0.24. Therefore, as the d i g e s t i b i l i t y of a r a t i o n i s increased, the amount of residue remaining to be cleared from the rumen decreases which has a d i r e c t e f f e c t on reducing the amount of time spent ruminating. The fibrousness of feedstuffs may also have an e f f e c t on the eating behavior i n ruminants. Freer et a l . (1962) found that F r i e s i a n and Shorthorn c a t t l e required more time to eat oat straw than they d i d to eat hay. Balch (1971) also found that le s s fibrous feedstuffs required s i g n i f i c a n t l y less time to be consumed by c a t t l e than d i d higher f i b e r feeds. Lee and Pearce (1984) demonstrated that d i f f e r e n t forages required d i f f e r e n t grinding energies to produce the same modulus of fineness and that grinding energy was r e l a t e d to the ADF content of the forage. I f swallowing i s l i m i t e d by a maximum p a r t i c l e s i z e , feedstuffs that are more r e s i s t a n t to comminution would require longer chewing times during eating. The moisture content of feedstuffs may also have an e f f e c t on eating behavior. G i l l et a l (1966) found that although there was no s i g n i f i c a n t d i f f e r e n c e i n eating time per kg DM intake, there was a s i g n i f i c a n t increase i n the number of chews per minute, and a s i g n i f i c a n t decrease i n the number of chews per bolus swallowed during eating when fresh herbage was fed to c a t t l e as compared with the feeding of the forage as a hay. Feeding of fresh -107- cut herbage also increased the rate of bolus swallowing and the wet weight of the b o l i . The dry weights of the b o l i from the two d i e t s , however, were not s i g n i f i c a n t l y d i f f e r e n t . These reaserchers also found that when mature ryegrass was fed i n the fresh form, as opposed to a hay, the median p a r t i c l e s i z e of the swallowed b o l i increased from 1314 um to 2070 um and the p a r t i c l e s i z e of the b o l i d i d not decrease as the meal progressed as i t d i d when the hay was fed. Forage to Concentrate Ratio I t has been shown that an increase i n the forage to concentrate r a t i o i n a r a t i o n i s associated with an increase i n the amount of time ruminants spend chewing during eating and ruminating (Balch, 1958; Sudweeks et a l . . 1975). Concentrates generally contain le s s f i b e r than do forages. Therefore, an increase i n the forage to concentrate r a t i o of a r a t i o n r e s u l t s i n an increase i n f i b e r intake and the l e v e l of i n d i g e s t i b l e residues i n the rumen. As discussed above, such an increase i n the f i b e r content of rations normally causes an increase i n the amount of time the animals spend eating and ruminating. The p a r t i c l e s i z e of concentrates also tends to be smaller than that of most forages. As the proportion of forage i n the d i e t increases, the p a r t i c l e s i z e of the d i e t increases and, therefore, the requirement f o r comminution of p a r t i c l e s by chewing during eating and rumination also increases. The lower requirement f o r comminution of concentrates i s r e f l e c t e d i n the higher rate of passage of concentrates from the rumen as compared with that of forages (Rode et a l . . 1985) . The proportion of concentrates i n a r a t i o n also has an e f f e c t on the eating behavior of ruminants. Balch (1958) found that when animals ate concentrates the recordings had a wavy appearance i n d i c a t i n g the mouth was -108- not opened wide; hay eating gave a more regular pattern with a l e v e l b aseline. The rate of jaw movements when eating concentrates was also somewhat higher (88-90 per min) than that f o r hay (72-82 per min). These chewing rates d i d not s i g n i f i c a n t l y change during the course of a meal. P a r t i c l e Density The s p e c i f i c g r a v i t y of p a r t i c l e s i n the rumen appears to have a d i r e c t e f f e c t on the s e l e c t i o n of p a r t i c l e s f o r rumination and passage from the rumen. Evans et a l . (1973) found that i n c a t t l e fed pasture hay, rumination commenced at the time of maximum concentration of low density p a r t i c l e s and minimum concentration of high density p a r t i c l e s i n the rumen. Rumination a c t i v i t y then ceased at the point where the concentration of high density p a r t i c l e s was maximum and low density p a r t i c l e s were at a minimum concentration i n the rumen. Since the increase i n s p e c i f i c g r a v i t y of feed p a r t i c l e s i n the rumen i s l i k e l y a r e s u l t of m i c r o b i al d i g e s t i o n and hydration of feed p a r t i c l e s (Hooper and Welch, 1985) i t i s p o s s i b l e that di f f e r e n c e s i n the rate of change of the s p e c i f i c g r a v i t y of d i f f e r e n t feeds w i l l have an e f f e c t on the time a f t e r feeding that rumination commences. Welch and Smith (1969a) found that the peak rumination time i n sheep fed d i e t s of varying n u t r i t i o n a l composition occured at d i f f e r e n t times depending on the d i e t fed. Passage from the rumen, once p a r t i c l e s i z e i s s u f f i c i e n t l y reduced, appears to be f a s t e s t f o r p a r t i c l e s with s p e c i f i c g r a v i t i e s i n the range of 1.1 to 1.2 (King and Moore, 1957; Campling and Freer, 1962). Hooper and Welch (1985) found that the s p e c i f i c g r a v i t y of forages increased at a greater rate when immersed i n rumen f l u i d than i t d i d when the forage was immersed i n water. These researchers also found that forage p a r t i c l e s i n -109- b u f f e r s o l u t i o n increased i n s p e c i f i c g r a v i t y at a f a s t e r rate than d i d p a r t i c l e s i n water. Thomson et a l . (1977) found that the a d d i t i o n of s a l i v a r y s a l t s to the rumen increased the l i q u i d d i l u t i o n rate. Therefore, s a l i v a t i o n during rumination may increase the s p e c i f i c g r a v i t y of comminuted p a r t i c l e s and increase the rate of passage of these p a r t i c l e s . I t i s not known, however, whether the s p e c i f i c g r a v i t y of feedstuffs w i l l a f f e c t the amount of comminution p a r t i c l e s w i l l require before passage i s p o s s i b l e . I t i s l i k e l y that the s p e c i f i c g r a v i t y of feedstuffs w i l l have i t s greatest e f f e c t on the passage of p a r t i c l e s already reduced to a s i z e capable of passing through the reticulo-omasal o r i f i c e . Therefore, the s p e c i f i c g r a v i t y of feedstuffs would p r o b a b i l i t y exert a greater e f f e c t on rumen f i l l and the l e v e l of intake rather than on the amount of time animals spend ruminating. Body Weight Bae et a l . (1983) found that chewing time per kg of c e l l w all intake i n d i f f e r e n t breeds of dairy c a t t l e s i g n i f i c a n t l y decreased with increasing metabolic body weight; differences i n body weight accounted f o r 52% of the v a r i a b i l i t y i n time spent chewing between animals. Differences i n c e l l w all intake between animals accounted f o r an a d d i t i o n a l 22% of v a r i a b i l i t y . Breed of animal d i d not s i g n i f i c a n t l y a f f e c t chewing time over and above the e f f e c t of body s i z e . There was also no c o r r e l a t i o n between body s i z e and speed of chewing. Lea and Pearce (1984) hypothesized that anatomical d i f f e r e n c e s i n the animal i n mouth s i z e , jaw movement, teeth area and grinding a c t i o n may account for differences i n p a r t i c l e s i z e reduction of ingested feed. -110- METHODS OF MONITORING CHEWING BEHAVIOR As with most behavioral studies, the most complete information on animal chewing behavior i s obtainable by v i s u a l observation and recording. Unfortunately, the amount of information required i n chewing studies, i n c l u d i n g t o t a l times of d i f f e r e n t behaviors and the counting of i n d i v i d u a l chews, makes t h i s task almost impossible to be accomplished by the v i s u a l observation of even one animal at a time. Since many of the experiments being designed today to study the e f f e c t s of various dietary treatments on chewing behavior require simultaneous observation of a number of animals, the manpower requirements and the cost of that labor p r o h i b i t the use of v i s u a l observation (Penning, 1983). Furthermore, v i s u a l observation of chewing behavior can become tedious and t i r i n g , r e s u l t i n g i n errors and inaccuracies i n the recorded information (Castle et a l . . 1975). To overcome the d i f f i c u l t i e s of v i s u a l observation, a number of automated methods have been developed to record the jaw movements of animals. The accurate observation of chewing behavior requires the development and use of one of these methods since none are commercially a v a i l a b l e . Any method that i s developed should i d e a l l y s a t i s f y the following c r i t e r i a : 1: be accurate i n the recording of chewing a c t i v i t y , making i t po s s i b l e to d i s t i g u i s h between chewing a c t i v i t y involved i n eating and rumination and non-chewing a c t i v i t y such as drinking, l i c k i n g , and bawling. 2: require a minimum of labor and/or supervision during recording and analysis of data. - I l l - 3: be e a s i l y interchangeable between animals and very r e s i s t a n t to damage by animal a c t i v i t y and other operational f a i l u r e . 4: be e a s i l y constructed at a minimum of expense. 5: be adaptable to telemetry or other remote recording to enable observation of grazing and eating i n a l l forms of animal confinement and housing. 6: be adaptable to e l e c t r o n i c analysis of recorded data by data loggers and computers. The e a r l i e s t method of automatic chewing montitoring u t i l i z e d an expandable rubber tube which was placed under the jaw or over the nose of the animal (Johnstone-Wallace, 1953; O l t j e n et a l . . 1962). The expandable tube was then connected v i a another tube to a pressure tambour on which a pen was mounted. Jaw movements by the animal would s t r e t c h the rubber tube which was placed around the jaw causing an increase i n pressure i n the closed system which i n turn moved the recording pen. Balch (1971) designed a s i m i l a r system but used a l i g h t l y i n f l a t e d tube made from t h i n walled rubber tubing supported on a perforated brass tube to prevent problems of kinking. This device was used both to monitor jaw movement when placed beneath the cheek strap of a leather head s t a l l and reticulo-rumen m o t i l i t y when anchored i n the rumen. A c t i v i t y increased the pressure i n the closed system by decreasing the volume of the device, s i m i l a r to the sqeezing of a balloon. Pressure changes were recorded by movement of the tambour pen on a moving chart recorder. Although the above systems have been used -112- s u c c e s s f u l l y , they s u f f e r from the need f o r animals to be p a r t i a l l y r e s t r a i n e d to prevent kinking of the tube which connects the jaw pneumatic device to the tambour, and from temperature changes which also a l t e r pressure i n the system thus rendering i t non-functional. The problems with the above system have been overcome with the use of pressure transducers which eliminate the need f o r a connecting length of tube (Law and Sudweeks, 1975). Pressure impulses from a pneumatic device are converted to e l e c t r i c a l impulses which can be recorded on an e l e c t r o n i c moving chart recorder. These researchers found that t h e i r system operated with l e s s than 1/2 percent error over the range of 1/4 to 16 impulses per second. The use of e l e c t r o n i c transducers also enables remote recording of chewing a c t i v i t y on tape by radio telemetry. Grazing behavior has been studied using V i b r i c o r d e r s which record movement by the motion of a pendulum which i s recorded on a c i r c u l a r disk of paper by a pen attached to the pendulum (Castle et a l . . 1975). This system alone, however, can only discern animal motion associated with body movement during grazing. Ruckebush and Bueno (1973) ( c a t t l e ) and Bechet (1978) (sheep) removed the pendulum from a V i b r i c o r d e r and adapted a pneumatic c o n t r o l to the pen which received impulses from a rubber bulb s i t u a t e d i n the submandibular space of the grazing animal. This l a t t e r method improved the accuracy of recording with V i b r i c o r d e r s , increased the amount of information recorded and d i d not require the use of expensive telemetry when used with grazing animals. Another form of transducer recorder has been employed which completely removes the need f o r pneumatics. L e v e i l l e et a l . (1979) developed a v a r i a b l e induction gauge by winding copper wire around a length of tube, f l a t t e n i n g the tube and wire, and covering the assembly with a polymer to -113- protect i t . The transducer was mounted around the nose band on sheep s i m i l a r to the mounting of pneumatic tubes. E l e c t r i c a l impulses caused by changes i n resistance i n the transducer due to jaw movement were inte r p r e t e d by a data logger and analyzed by computer. Penning (1983) developed an almost i d e n t i c a l system except that the transducer was made by packing a s i l i c o n tube with carbon granules and implanting electrodes at each end. The transducer was mounted i n a s i m i l a r manner with the impulses recorded on tape and l a t e r analyzed by a microprocessor. Chewing behavior has also been recorded without the need f o r pneumatics using various forms of microswithches (Duckworth and Shirlaw, 1955; Stobbs and Cowper, 1972; Chambers et a l . . 1981). These types of "event recorders" are mounted d i r e c t l y under the jaw and a c t i v a t e d by d i r e c t pressure or mounted on a h a l t e r and acti v a t e d by a chain or rope slung under the jaw of the animal. Microswitch impulses, however, record only a s i n g l e f i x e d amplitude stroke when the jaw of the animal opens f a r enough to a c t i v a t e the switch. Therefore, the adjustment of t h i s type of system i s c r i t i c a l ; damage to the microswitch can also be a major problem (P.M. Kennedy, personal communication). This method also gives no information on the amplitude of the jaw movements which are important i n i d e n t i f y i n g many non chewing a c t i v i t i e s such as bawling, l i c k i n g and drinking. Both the i n c l u s i o n of these a c t i v i t i e s as chewing and any damage to the microswitch could introduce considerable error. Two methods f o r d i r e c t measurement of jaw movement and chewing behavior have been developed. Nichols (1966) attached s p e c i a l electrodes to the masseter muscles of sheep. Changes i n the e l e c t r i c a l p o t e n t i a l received from the s k i n over the muscles were amplified by a transmitter which relayed the signals to a r e c e i v e r which recorded the signals on an e l e c t r i c chart -114- recorder. Kydd and Mullins (1963) developed a method f o r f i t t i n g a very small pressure transducer to a tooth and connecting i t to a transmitter embedded i n a tooth borne p a r t i a l denture. This method would have a great advantage i n that the actual grinding energy and chewing a c t i v i t y could be measured d i r e c t l y . However, use of both of the above methods on a large scale i s l i m i t e d by the d i f f i c u l t y of f i t t i n g the transducers, the lack of easy i n t e r c h a n g e a b i l i t y between animals and the cost of animal preparation. -115- MATERIALS AND METHODS DAIRY COW TRIAL Twelve H o l s t e i n dairy cows, a l l i n mid l a c t a t i o n , were randomly a l l o t t e d to four d i e t a r y treatments i n a balanced two period changeover design ( G i l l and Magee, 1976). Each animal received two of the four treatments during the experiment. The d i e t a r y treatments comprised good q u a l i t y orchardgrass hay chopped to two d i f f e r e n t median p a r t i c l e lengths (10 mm and 20 mm) fed at two forage to concentrate r a t i o s (40:60 and 60:40) i n a two by two f a c t o r i a l arrangement; the cows were fed ad l i b i t u m i n two meals per day. Each four week experimental period consisted of three weeks adaptation followed by one week of sample c o l l e c t i o n . During the adaptation period, the cows were housed with the r e s t of the herd i n a free s t a l l barn but fed i n d i v i d u a l l y using e l e c t r o n i c a l l y a c t i v a t e d doors. At the beginning of the sampling period, s i x of the cows on t r i a l were tra n s f e r r e d to the research area f o r e l e c t r o n i c monitoring of chewing behavior (see Figure 14). The animals were adapted to stanchions for 24 hours a f t e r which chewing behavior was monitored continuously f o r 24 hours. The cows were then returned to the free s t a l l barn f o r the next adaptation period and the second group of s i x cows was t r a n s f e r r e d to the research area. Chewing monitoring commenced immediately following the afternoon milking and terminated j u s t p r i o r to the next afternoon milking. During the e a r l y morning of each monitoring period, i t was necessary for the cows to be released from the stanchions to permit p a r l o r milking. Any chewing a c t i v i t y that occurred during that time was monitored v i s u a l l y . During the sampling period, milk, rumen f l u i d , and f e c a l samples were also -116- FIGURE 14: Dairy c a t t l e i n stanchion s t a l l s i n research area during the monitoring of chewing behavior. -117- taken to be analyzed i n r e l a t i o n to objectives of another t r i a l . DAIRY STEER TRIAL Three H o l s t e i n steers i n i t i a l l y weighing 845, 947 and 927 kg and one Ayrshire steer weighing 776 kg were randomly a l l o c a t e d to four d i e t a r y treatments i n a balanced L a t i n Square design. Each animal had been s u r g i c a l l y prepared with rumen and duodenal cannulae for the taking of samples to be analyzed i n r e l a t i o n to other objectives of the t r i a l . The d i e t a r y treatments consisted of timothy-brome hay chopped to four d i f f e r e n t median p a r t i c l e lengths (5.0, 10.0, 15.0, and 20.0 mm) which were fed i n a 60:40 forage to concentrate r a t i o at 9.5 kg per 100 kg of metabolic body weight per day. The rations were fed i n four equal allotments during the day at 6 hour i n t e r v a l s , s t a r t i n g at 9:00 AM. Each experimental period was 21 days i n length with 14 days f o r d i e t adaptation followed by 7 days of sample c o l l e c t i o n during which chewing behavior was monitored. The steers were housed i n stanchions i n the research area described above f o r the duration of the experiment with the exception of the f i r s t 10 days of adaptation i n the f i r s t two periods during which the steers were housed unrestrained i n i n d i v i d u a l pens. Chewing monitoring commenced immediately p r i o r to the 3:00 PM feeding on the morning of the second sampling day and ran continuously fo r 48 hours. PREPARATION OF CHOPPED FORAGE A l l the forage that was fed i n the two experiments above was chopped with e i t h e r a John Deere Model 35 or a Fox forage harvester. The forage was -118- obtained in standard two strand or three wire square bales which were randomly allocated into dietary treatments prior to chopping. Randomly selected test bales were chopped, using various machine settings, into an open fronted bin. Each test sample of chopped hay was then subsampled and separated on the Forage Particle Separator (see Chapter 1) to determine the median particle length. Appropriate machine settings were then selected to prepare chopped forage of the required median particle lengths for use as dietary treatments in the experiments. MONITORING OF CHEWING BEHAVIOR The development of a chewing monitor system was required to enable continuous monitoring of the chewing behavior of the animals on t r i a l . This system was installed in a separate research f a c i l i t y in which the animals on t r i a l were held in individual stanchions (Figure 14). The system consisted of a pneumatic device (Figure 15) which was held in place under the jaw of the animal by a specially designed halter (Figure 16). The halters were adjustable in three places (over the nose, behind the pohl, and under the neck) to enable correct positioning of the pneumatic device. Pressure impulses generated by jaw movements were transmitted via a length of tygon tubing to a " s i l i c o n chip" electronic pressure transducer (Figure 17) mounted between the ears of the animal on the pohl strap of the halter (Figure 16). Equilibration of static pressure in the closed pneumatic system was achieved by activation of the air valve mounted on the right hand side of the pneumatic device. The pressure transducer was connected via a quick coupler electrical connector and an expandable cord to an amplifier which was mounted on the -119- FIGURE 15: Pneumatic device of the chewing monitor for producing pressure impulses from jaw movement. -120- FIGURE 16: Chewing monitor h a l t e r with pneumatic device and pressure transducer mounted. -121- FIGURE 17: Chewing monitor " s i l i c o n chip" pressure transducer mounted i n i t s s t e e l housing. -122- stanchion support d i r e c t l y above the animal's head. This method of connection allowed u n r e s t r i c t e d movement of the animal's head and easy disconnection to release the animals to go to the milking p a r l o r . The a m p l i f i e r was "hard-wired" to a s p e c i a l power supply and to a v a r i a b l e speed chart recorder on which output t r a c i n g were recorded. Both the a m p l i f i e r and power supply were designed and constructed by G i l l e s Galzy, Senior Technician of the Department of Animal Science, U n i v e r s i t y of B r i t i s h Columbia. During the monitoring of chewing behavior, animal a c t i v i t y was also v i s u a l l y monitored using closed c i r c u i t video equipment. Tracings recorded on the chart recorder were simultaneously compared with the animal a c t i v i t y seen on the video monitors to ensure accurate recording of chewing behavior. ANALYSIS OF CHEWING RESULTS During each chewing monitoring period, each one hour segment of recorded data was c o l l a t e d into t o t a l times spent eating and ruminating. The remaining time was c l a s s i f i e d as i d l i n g , which included time spent drinking, bawling, and grooming, a l l of which were discernable from the tracings. The number of boluses that were regurgitated during periods of rumination were also c a l c u l a t e d from the tracings. The chewing a c t i v i t i e s f o r each hour of recording were then t o t a l l e d f o r the e n t i r e recording period and expressed as t o t a l time per 24 hours. These times were then divided by the dry matter intake f o r each animal to give the time spent chewing and i d l i n g per kilogram of intake as was suggested by Balch (1971) as an index of the fibrousness of f e e d s t u f f s . Time chewing per bolus regurgitated was c a l c u l a t e d by d i v i d i n g the t o t a l time spent ruminating by the number of -123- boluses regurgitated during a twenty four hour period. STATISTICAL ANALYSIS The e f f e c t of forage p a r t i c l e length and forage to concentrate r a t i o on parameters of chewing behavior was tested by General Linear Hypothesis using the BMD:10V packaged program of the U n i v e r s i t y of B r i t i s h Columbia. Y i e l d v a r i a b l e s were expressed as chewing a c t i v i t y per kg of DM intake with metabolic body weight (BW -^) included i n the analysis as a covariable. Differences between means for the treatment combinations were tested by Duncan's M u l t i p l e Range Test ( a = 0.05). The General Linear Hypothesis f o r the Dairy cow t r i a l was as follows: Y i j k l m = u + A ± + Pj + L k + H X + L H k l + b B w i j k l m + E i j k l m where: Y i j k i m = the dependent v a r i a b l e : chewing parameters. u = the o v e r a l l mean A i = the e f f e c t of the i ' t h animal. Pj = the e f f e c t of the j ' t h period. L k = the e f f e c t of the k'th forage median p a r t i c l e length. Hi = the e f f e c t of the I'th forage:concentrate r a t i o . L H k i = the e f f e c t of the i n t e r a c t i o n between the k'th forage median p a r t i c l e length and the I'th forage to concentrate r a t i o . b B W i j k l m the e f f e c t of the covariable metabolic body weight -124- ^ i j k l m = t b e unexplained r e s i d u a l error associated with each sample. The General Linear Hypothesis f o r the Dairy Steer t r i a l was as follows: Y i j k - u + A i + Pj + L k + bBw i j k + E i j k where: Y ^ j k = the dependent v a r i a b l e : chewing parameter. u = the o v e r a l l mean. A^ = the e f f e c t of the i ' t h animal. Pj = the e f f e c t of the j 1 t h period. L k = the e f f e c t of the k'th forage median p a r t i c l e length. bBWij k = the e f f e c t of the covariable metabolic body weight. E ^ j k = the unexplained r e s i d u a l error associated with each sample. -125- RESULTS DAIRY COW TRIAL The p a r t i c l e length d i s t r i b u t i o n s of the two median chop lengths of forage fed i n t h i s experiment are shown i n Table XXI. The median p a r t i c l e length (MPL) of the short chopped forage was 7.32 mm which was s i g n i f i c a n t l y smaller (P < 0.05) than that of the long chopped forage which had a median p a r t i c l e length of 18.06 mm. The c o e f f i c i e n t of spread (CS) of the short chop forage (1.284) was also s i g n i f i c a n t l y smaller than that f o r the long chop (1.488). The higher CS for the long chop indi c a t e d that i t had a r e l a t i v e l y narrower d i s t r i b u t i o n of p a r t i c l e lengths which were also more normally d i s t r i b u t e d . There was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n n u t r i t i o n a l TABLE XXI: P a r t i c l e length d i s t r i b u t i o n (% sample wt.) and d i s t r i b u i o n parameters of the short and long chopped orchardgrass hay. FORAGE PARTICLE LENGTH SHORT LONG 3.30- 8.25 mm 8.25-16.50 mm 16.50-33.00 mm 33.00-66.00 mm <3.30 mm >66.00 mm 23.6 29.9 34.0 11.7 0.8 0.0 9.5 9.0 25.5 38.8 15.1 2.1 MEDIAN LENGTH: COEFFICIENT OF SPREAD: 7.3 mma 1.284 a 18.1 mmb 1.488 b WEIBULL PARAMETERS: B 0.136678 0.055357 C 1.283979 1.487754 Median lengths and c o e f f i c i e n t s of spread with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -126- TABLE XXII: Nutrient content (%, DM basis) of the concentrate and short and long chopped orchardgrass hay used i n the experiment. CONCENTRATE HAY SHORT LONG DM CP NDF ADF 86.5 14.9 88.1 14.6 68.5 38. 9 b 86.7 14.0 68.5 38. 3 b 11.0 a a " D Means with i n rows with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). composition between the two chop lengths of forage (Table XXII). There was, however, a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) i n a c i d detergent f i b e r (ADF) content between the forage and concentrate, but no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n dry matter and crude p r o t e i n content. The two forage to concentrate r a t i o treatments therefore also had s i g n i f i c a n t l y d i f f e r e n t ADF contents (P < 0.05). Throughout the s t a t i s t i c a l analysis of t h i s experiment the e f f e c t of the covariable (BW-7^) was not s i g n i f i c a n t (P > 0.05) i n d i c a t i n g that the metabolic weight of the animals d i d not have a s i g n i f i c a n t e f f e c t on chewing behavior i n t h i s experiment. There was also no s i g n i f i c a n t (P > 0.05) animal e f f e c t , except on time spent chewing per bolus regurgitated during rumination. Subsequently, the covariable and, where appropriate, the animal e f f e c t were removed from the General Linear Hypothesis f o r the analysis of t h i s t r i a l . The p a r t i t i o n i n g of sums of squares by the reduced General Linear Hypothesis model f o r each y i e l d v a r i a b l e i s given i n Appendix A. Decreasing the MPL of the forage being fed d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) the intake or chewing time of the animals (Table XXIII). There was a consistent trend, however, towards increased i d l e time and decreased time spent eating and ruminating when the MPL of the forage was decreased. -127- TABLE XXIII: E f f e c t of forage median p a r t i c l e length on intake and chewing c h a r a c t e r i s t i c s . INTAKE (kg, DM): Hay Cone. To t a l CHEWING TIME (min/kg intake): I d l i n g Eating Rumination T o t a l Chewing RUMINATION CHARACTERISTICS: # B o l i / kg intake Time chewing / Bolus (min) MEDIAN PARTICLE LENGTH (mm) 7.3 18.1 SEM 10.1 10.1 0.1 10.2 10.3 0.1 20.3 20.4 0.3 33.0 29.2 1.7 10.9 12.1 0.7 17.9 19.4 0.8 28.8 31.4 1.3 17.6 19.7 1.0 1.00 0.97 0.01 TABLE XXIV: E f f e c t of forage to concentrate r a t i o on intake and chewing c h a r a c t e r i s t i c s . FORAGE:CONCENTRATE RATIO INTAKE: (kg, DM) Hay Cone. To t a l 40:60 8 12 .5 a 7b 21.2C 60:40 11.7 b 7.8 a 19. 6 a SEM 0.1 0.1 0.3 CHEWING TIME: (min/kg intake) I d l i n g Eating Rumination T o t a l Chewing RUMINATION CHARACTERISTICS: # B o l i / kg intake Time chewing / Bolus (min) 32.4 9.7 a 16. 6 a 26. 3 a 16.0 a 0.99 29.7 13. 2 l 20. 7 l 33. 9l 21.3 d 0.98 1.7 0.7 0.8 1.3 1.0 0.01 a " b Mean values within rows having d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -128- Increasing the proportion of forage and, therefore, the proportion of f i b r e i n the d i e t s i g n i f i c a n t l y decreased (P < 0.05) voluntary intake and s i g n i f i c a n t l y increased (P < 0.05) the amount of time the animals spent eating and ruminating per kg of DM ingested (Table XXIV). There was therefore also a s i g n i f i c a n t cumulative e f f e c t (P < 0.05) of time spent eating and ruminating on increasing the t o t a l time spent chewing per kg of feed ingested as the proportion of forage i n the d i e t increased. Although increasing the proportion of hay ingested d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) the amount of time spent i d l e there was a trend towards reduced i d l e time. During rumination, increasing the proportion of forage i n the d i e t s i g n i f i c a n t l y increased (P < 0.05) the number of b o l i regurgitated per kg of feed ingested but d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) the time spent TABLE XXV: E f f e c t of forage to concentrate r a t i o and forage median p a r t i c l e length (mm) on intake and chewing c h a r a c t e r i s t i c s . DIETARY TREATMENTS FORAGE:CONCENTRATE RATIO 40: :60 60: :40 MEDIAN PARTICLE LENGTH 7. ,3 18. 1 7. 3 18. 1 SEM INTAKE (kg, DM): Hay 8. ,4 8. ,5 11. ,8 11. ,8 0. ,2 Cone. 12. .6 12. ,8 7. ,8 7. ,8 0. ,2 T o t a l 21. .0 21. ,3 19. ,6 19. .6 0. ,4 CHEWING TIME (min/kg intake): I d l i n g 33, .6 31. .3 32. .4 27, .0 2, .4 Eating 9. .9 9. .6 11. .9 14. .5 1. .0 Rumination 15 .2 18. .0 20. .6 20. .8 1. .2 T o t a l Chewing 25. .1 27. .6 32. .5 35, .3 1. .8 RUMINATION CHARACTERISTICS: # B o l i / kg intake 14, .3 17, .7 20, .8 21, .7 1, .5 Time chewing / Bolus (min) 1, .02 0, .95 0, .98 0, .98 0, .01 -129- chewing per bolus regurgitated (Table XXIV). Increasing the MPL of the forage being fed also increased the number of b o l i regurgitated during rumination but the e f f e c t was not s i g n i f i c a n t (P > 0.05) (Table XXIII). Though also not s i g n i f i c a n t (P > 0.05), there was a strong trend towards a reduced time spent chewing per bolus regurgitated when the MPL of the forage increased. There was no s i g n i f i c a n t i n t e r a c t i o n (P > 0.05) between MPL and the proportion of forage i n the d i e t on the chewing c h a r a c t e r i s t i c s of the animals i n t h i s t r i a l (Table XXV). DAIRY STEER TRIAL The p a r t i c l e length d i s t r i b u t i o n s of the four treatments of chopped forage fed i n t h i s experiment are given i n Table XXVI. There was a s i g n i f i c a n t d i f f e r e n c e (P < 0.05) between the MPL of the four chop lengths TABLE XXVI: P a r t i c l e length d i s t r i b u t i o n s (% sample wt.) and d i s t r i - bution parameters of the chopped timothy-brome hay. CHOPPED FORAGE TREATMENTS PARTICLE LENGTH A B C D <3.30 mm 36.8 23.0 20.6 13.9 3.30- 8.25 mm 28.4 20.3 10.2 8.0 8.25-16.50 mm 23.5 33.3 24.7 18.1 16.50-33.00 mm 8.9 17.3 33.0 35.8 33.00-66.00 mm 2.5 5.5 9.9 20.8 >66.00 mm 0.0 0.6 1.7 3.6 MEDIAN LENGTH (mm): 5.2 a 9.0b 13. 3 C 20.0 d COEFFICIENT OF SPREAD: 0.955 1.109 1.098 1.219 WEIBULL PARAMETERS B: 0. .192308 0. ,110988 0.075482 0.050100 C: 0. .955450 1. .109449 1.097834 1.218846 Median lengths and c o e f f i c i e n t s of spread with d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). -130- of forage but no s i g n i f i c a n t difference (P > 0.05) between the CS. The shortest length of forage, however, had the smallest CS and the longest chop length had the la r g e s t . The CS for the middle chop lengths were intermediate. There was also no s i g n i f i c a n t difference (P > 0.05) i n n u t r i t i o n a l composition between the four forage p a r t i c l e length treatments (Table XXVII) . The concentrate that was fed with the hay had a s i g n i f i c a n t l y higher crude p r o t e i n (P < 0.05) and s i g n i f i c a n t l y lower ADF content (P < 0.05) than d i d the forage; the two feedstuffs d i d not s i g n i f i c a n t l y d i f f e r (P > 0.05) i n moisture content. However, since the forage to concentrate r a t i o remained constant throughout the experiment, there was no s i g n i f i c a n t d i f f e r e n c e (P > 0.05) i n n u t r i t i o n a l composition between the di e t a r y treatments (Table XXVIII) . Therefore, as was the objective, t h i s experiment was only t e s t i n g the e f f e c t of median p a r t i c l e length on chewing behavior. The feeding l e v e l during the experiment was f i x e d at 9.5 percent of metabolic body weight on an as fed basis . A l l animals except the Ayrshire consumed t h e i r t o t a l feed allotment throughout the experiment. The Ayrshire's intake, on the basis of metabolic body weight, was lower than TABLE XXVII: Nutrient content (%, DM basis) of the concentrate and the four lengths (mm) of chopped timothy-brome hay used i n the experiment. CONCENTRATE FORAGE MEDIAN PARTICLE LENGTH (mm) 5.2 9.0 13.3 20.0 D.M. C P . NDF ADF 10. l a 88.3 16.0 b 88.3 12. l a 53.7 36. 8 b 88.0 11. 6 a 55.2 39. 2 b 87.9 11.4 a 54.2 37.0 b 89.2 11. 5 a 56.3 38.0 b a-b Means within rows with d i f f e r e n t superscripts d i f f e r e n t (P < 0.05). were s i g n i f i c a n t l y -131- TABLE XXVIII: Nutrient content (%, DM basis) of the d i e t a r y treatments (40% concentrate with 60% timothy-brome hay chopped at four median p a r t i c l e lengths). FORAGE MEDIAN PARTICLE LENGTH (mm) 5. .2 9. .0 13. .3 20. .0 D.M. 88. .3 88. .1 88. .1 88. .8 C P . 13. .7 13. .4 13. .2 13. .3 ADF 26. .1 27. .6 26. .2 26. .8 that f o r the other steers and was not constant over the four treatment periods of the experiment. This may have been caused by a chronic frothy b l o a t s u f f e r e d by the Ayrshire throughout the experiment. I t was not c l e a r whether the length of hay (5.2 mm) fed to the Ayrshire i n the f i r s t period had any e f f e c t on the incidence of bloat i n t h i s animal. The covariable, metabolic body weight, had a s i g n i f i c a n t e f f e c t (P < 0.05) on time spent i d l e , time spent ruminating and t o t a l time spent chewing per kg of intake, and on the time spent chewing per bolus regurgitated during rumination. Metabolic body weight, however, d i d not have a s i g n i f i c a n t e f f e c t (P > 0.05) on the time spent eating, nor on on the number of b o l i regurgitated during rumination per kg of feed consumed. Where appropriate, the following r e s u l t s were therefore adjusted for the e f f e c t of metabolic body weight on chewing behavior. The p a r t i t i o n i n g of the sums of squares by the f u l l General Linear Hypothesis model f o r each y i e l d v a r i a b l e i s given i n Appendix B. The r e s u l t s of the e f f e c t of decreasing the MPL of the forage on the chewing a c t i v i t y of the steers i s shown i n Table XXIX. There was a consistent trend towards decreased time spent eating per kg of feed ingested as the MPL of the forage decreased, but t h i s e f f e c t was not s i g n i f i c a n t (P > 0.05). The same trend was seen i n the time spent ruminating which -132- TABLE XXIX: Ef f e c t of forage median p a r t i c l e length (mm) on intake and chewing c h a r a c t e r i s t i c s . FORAGE MEDIAN PARTICLE LENGTH (mm) 5.2 9.0 13.3 20.0 SEM COV INTAKE (kg, DM): 12.4 a 12.8 a b 12.7 a b 13.0 b 0.1 NS CHEWING TIME (min/kg intake): Idling Eating Rumination Total Chewing 94.4 b 8.4 16.9 a 25.3 a 86.1 a b 9 * 6 h 20.9° 30.5 b 83.5 a 22.6 b c 32.3 b c 77.3 a 10.3 24.6° 34.9 C 2.5 0.5 0.8 1.0 * NS * * RUMINATION CHARACTERISTICS: // B o l i / kg intake Time chewing / Bolus (min) 18.9 a 0.856 23.8 a b. 0.859 28.2 b c v 0.794 a b 31.1° 0.786 3 1.3 0.018 NS * ^ Covarible e f f e c t of BŴ *̂ :̂ NS = not s i g n i f i c a n t , * = s i g n i f i c a n t (P < 0.05). a-c Mean values within rows having d i f f e r e n t superscripts were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05). s i g n i f i c a n t l y decreased (P < 0 . 0 5 ) as the MPL of the forage decreased. The cumulative e f f e c t of decreasing the MPL of the forage on time spent eating and ruminating r e s u l t e d i n a s i g n i f i c a n t decrease (P < 0 . 0 5 ) i n t o t a l time spent chewing per kg of feed ingested as the MPL of the forage decreased. Subsequently, there was a concomitant s i g n i f i c a n t increase (P < 0 . 0 5 ) i n the amount of time the animals were i d l e per kg of feed ingested. During rumination, there was a s i g n i f i c a n t decrease (P < 0 . 0 5 ) i n the number of b o l i regurgitated per kg of feed ingested (DM basis) as the MPL of the forage decreased. The time spent chewing per bolus regurgitated was also s i g n i f i c a n t l y a f f e c t e d (P < 0 . 0 5 ) by the MPL of the forage. There was a reduced amount of time spent chewing per bolus when the animals were fed the 2 0 . 0 mm length of forage as compared with the 5 . 2 and the 9 . 0 mm lengths. The time spent chewing per bolus on the 1 3 . 3 mm forage was intermediate but not s i g n i f i c a n t l y d i f f e r e n t (P > 0 . 0 5 ) from the other lengths of forage. C u r v i l i n e a r regression was performed on the responses of the y i e l d v a r i a b l e s discussed above to the changes i n forage MPL. In general, TABLE XXX: Regression (Y = a + blogX) and BW0-75 covariable c o e f f i c i e n t s f o r the e f f e c t of forage median p a r t i c l e length on chewing and rumination c h a r a c t e r i s t i c s . REGRESSION BW r 0 . 7 5 a b CHEWING TIME (min/kg intake): I d l i n g Eating Ruminating T o t a l chewing 1 1 4 . 2 3 3 6 . 3 8 0 7 . 9 2 4 1 4 . 2 5 9 - 2 8 . 2 3 8 3 . 0 7 4 1 2 . 9 9 8 1 6 . 1 0 8 0 . 9 8 0 . 9 3 0 . 9 9 0 . 9 8 1 . 3 8 8 * 0 . 2 2 6 0 . 4 3 9 * 0 . 6 6 7 * RUMINATION CHARACTERISTICS: #Boli / kg intake min chewing / bolus 3 . 7 2 0 2 1 . 2 8 5 0 . 9 9 0 . 2 8 9 0 . 0 0 9 * * Covariable was s i g n i f i c a n t (P < 0 . 0 5 ) . - 1 3 4 - regressing chewing a c t i v i t y on the logarithm of the MPL of the forage gave a bett e r f i t to the data than d i d simple l i n e a r regression. The observed values are shown with the predicted regression l i n e s i n Figures 18 and 19 and the regression c o e f f i c i e n t s and the c o e f f i c i e n t s of determination f o r each regression l i n e are given i n Table XXX, along with the covariable c o e f f i c i e n t s f o r the e f f e c t of metabolic body weight on chewing a c t i v i t y . Animals with higher metabolic body weights spent s i g n i f i c a n t l y (P < 0.05) more time i d l e and les s time eating and ruminating per kg of feed ingested than d i d l i g h t e r animals. Larger animals also ruminated f o r s i g n i f i c a n t l y l e s s time (P < 0.05) on each bolus regurgitated during rumination. They also tended to regurgitate a smaller number of b o l i per kg of feed ingested but t h i s e f f e c t was not s t a t i s t i c a l l y s i g n i f i c a n t (P > 0.05). -135- 1 0 0 \ 9 0 CD CO 8 0 - Idle T o t a l C h e w i n g R u m i n a t i o n • ... D E a t i n g 5 1 0 1 5 2 0 M e d i a n P a r t i c l e L e n g t h ( m m ) FIGURE 18: P l o t o f o b s e r v e d v a l u e s and p r e d i c t e d r e g r e s s i o n l i n e s (Y = a + b l o g X ) f o r the r e l a t i o n s h i p between the times a n i m a l s s p e n t i d l e and chewing p e r kg i n t a k e (Y) and the median p a r t i c l e l e n g t h o f a timothy-bromegrass hay chopped to 4 median p a r t i c l e l e n g t h s (X) when the hay was f e d i n a 60% f o r a g e , 40% c o n c e n t r a t e r a t i o n . -136- CO •4-* c ra „«, x 2 0 o m + 10 o 0 .90 CO o m 9 CO 0 . 8 0 | CD SZ O - 0 .70 c u 0 5 10 15 Med ian Par t ic le Length (mm) 2 0 FIGURE 19: Plot of observed values and predicted regression l i n e (Y = a + blogX) f o r the r e l a t i o n s h i p between the number of b o l i regurgitated during rumination per kg of intake (Y) and median forage p a r t i c l e length (X), and the e f f e c t of median p a r t i c l e length on time spent chewing per bolus regurgitated when timothy-bromegrass hay was chopped to 4 median p a r t i c l e lengths and fed i n a 60% forage, 40% concentrate r a t i o n . -137- DISCUSSION As demonstrated by other research, and i n the present study, the reduction of p a r t i c l e s i z e i n forages fed to ruminants does not always a f f e c t the chewing behavior of c a t t l e . In both of the present studies reducing the MPL of the forage d i d not s i g n i f i c a n t l y change (P > 0.05) the rate of intake of the d i e t s that were fed. However, there was a consistent trend towards a reduced amount of time spent eating per kg of feed ingested as the MPL of the forage decreased. One must therefore conclude that the d i f f e r e n c e between the lengths of forage i n the amount of comminution required by the animals to swallow the rations was minimal and d i d not s i g n i f i c a n t l y i n h i b i t the rate of intake. On the other hand, increasing the proportion of the forage i n the r a t i o n fed to the d a i r y cows s i g n i f i c a n t l y increased the amount of time required f o r chewing each kg of feed p r i o r to swallowing. The greater rate of intake for concentrates as compared with that f o r forages has been reported before (Balch, 1958). The f a s t e r rate of intake f o r concentrates may be due to a smaller p a r t i c l e s i z e and/or les s resistance to comminution by chewing. Therefore, as the proportion of forage i n a r a t i o n increases, one would expect a longer time chewing per kg of intake to be required p r i o r to swallowing. Research has shown that decreasing the p a r t i c l e s i z e of forages fed to ruminants can increase voluntary feed intake and decrease the time spent ruminating. The cause of these e f f e c t s i s b e l i e v e d to be a greater rate of passage of p a r t i c l e s from the rumen; the increased rate of passage being caused by a decreased requirement f o r p a r t i c l e s to be reduced i n s i z e by rumination to enable passage through the reticulo-omasal o r i f i c e . Such a decrease i n time spent ruminating was observed i n the dairy steer t r i a l . -138- Decreasing the MPL of the timothy-brome hay from 20.0 to 9.0 mm, 13.3 to 5.2 mm, or 9.0 to 5.2 mm s i g n i f i c a n t l y decreased the amount of time the animals spent ruminating per kg of intake. One would therefore conclude that the decreases i n time spent ruminating would be associated with a greater rate of passage of unruminated p a r t i c l e s from the rumen and that the p o t e n t i a l fo r higher intakes would be increased. In the d a i r y cow t r i a l , however, decreasing the MPL of the orchardgrass hay from 18.1 to 7.3 mm d i d not s i g n i f i c a n t l y a l t e r the intake of the r a t i o n or the time the cows spent ruminating per kg of intake. Why, therefore, d i d a change of 10.8 mm i n MPL not s i g n i f i c a n t l y a f f e c t the time spent ruminating by the dairy cows when smaller changes had a s i g n i f i c a n t e f f e c t when the d a i r y steers were fed chopped timothy-brome hay? In the steer t r i a l , the e f f e c t of reducing forage p a r t i c l e length on decreasing the amount of time the animals spent ruminating increased as the MPL of the forage decreased. There was a d i r e c t r e l a t i o s h i p between the time spent ruminating and the logarithm of the median p a r t i c l e length of the forage that was fed (R 2 = 0.99). This r e l a t i o n s h i p was s i m i l a r to that described by Poppi et a l . (1980) f o r the e f f e c t of p a r t i c l e s i z e on resistance to passage from the rumen. On the basis of t h e i r findings, Poppi et a l . (1980) suggested that there e x i s t e d a c r i t i c a l p a r t i c l e s i z e above which passage may be p o s s i b l e , but the p r o b a b i l i t y of such passage was very low. Therefore, r e l a t e d to the resistance of p a r t i c l e s i z e passage from the rumen, there appears to be a "threshold length" below which the reduction of forage p a r t i c l e length may have a s i g n i f i c a n t e f f e c t on decreasing the time spent ruminating and, therefore, increasing voluntary feed intake. I t i s p o s s i b l e that the median p a r t i c l e lengths of the orchardgrass hay fed i n the d a i r y cow t r i a l were above the "threshold" required to e l i c i t a s i g n i f i c a n t -139- response i n the time spent ruminating by these animals. I t has been reported that the e f f e c t of decreasing forage p a r t i c l e length on increasing intake and decreasing the time spent ruminating becomes more pronounced as the f i b e r content of the forage increases (Welch and Smith, 1969a). Although d i f f e r e n t forages were fed i n the present two t r i a l s , the ADF content of the two forages was s i m i l a r (38.6% ADF f o r the orchardgrass hay i n the dairy cow t r i a l and 37.8% ADF f o r the timothy-brome hay i n the steer t r i a l ) . The timothy-brome hay, on the other hand, had a lower CP content (11.7 vs 14.3%) and produced a much coarser and s t i f f e r p a r t i c l e when processed than d i d the orchardgrass hay. Pearce (1965) suggested that increased p r o t e i n intake could decrease rumination time, and the coarseness of the timothy-brome hay may indicate a greater resistance to comminution. Therefore, the reduction i n p a r t i c l e length of the lower p r o t e i n content and s t i f f e r timothy-brome hay p a r t i c l e s may have e l i c i t e d a greater response i n chewing behavior than that which was e l i c i t e d by the orchardgrass hay. The experimental design of the dairy cow t r i a l may also have influenced the detection of s i g n i f i c a n t differences between the e f f e c t s of the dietary treatments on chewing behavior. There i s extreme v a r i a t i o n i n the chewing behavior of ruminants which, i f uncontrolled, can introduce s i g n i f i c a n t experimental er r o r into the r e s u l t s of experiments. The design used f o r the steer t r i a l was a balanced L a t i n Square whereas that used f o r the cow t r i a l was a two period changeover design with four treatments. In the steer t r i a l each animal received each treatment while i n the dairy cow t r i a l each cow only received two of the four treatments. The unbalanced nature of the cow t r i a l therefore may not have f u l l y c o n t r o l l e d the animal to animal v a r i a t i o n to the point that the differences i n chewing behavior between p a r t i c l e -140- length treatments were not s t a t i s t i c a l l y s i g n i f i c a n t . There was, however, a s i g n i f i c a n t increase i n the amount of time spent ruminating per kg of intake as the proportion of forage i n the r a t i o n fed to the d a i r y cows was increased. The increase i n the proportion of forage was also associated with an increase i n the f i b e r content of the r a t i o n which has been shown to increase the time spent ruminating. Bae et a l . (1981) demonstrated that, regardless of l e v e l of intake, ingested roughage required a constant amount of comminution per kg of c e l l w all content f o r passage from the rumen. Therefore, one would expect animals to spend a greater amount of time ruminating per kg of intake as the proportion of forage i n the d i e t increases. The detection of a s i g n i f i c a n t e f f e c t of forage to concentrate r a t i o , but not of p a r t i c l e length, on rumination time i n the dai r y cow t r i a l supports the suggestion that the composition of the d i e t has the greatest e f f e c t on the process of d i g e s t i o n i n the ruminant (Mertens and Ely, 1982). Both increasing the forage to concentrate r a t i o i n the dairy cow t r i a l and increasing the MPL i n the steer t r i a l s i g n i f i c a n t l y increased the number of b o l i regurgitated during rumination. Except when the p a r t i c l e length of the hay fed to the steers was increased to 20.0 mm, there was no s i g n i f i c a n t change i n the time spent chewing per bolus regurgitated i n each t r i a l . Therefore, there was no change i n the e f f i c i e n c y of mastication during rumination when the proportion of forage i n the d i e t or the MPL of the forage was a l t e r e d . The increase i n the e f f i c i e n c y of mastication during rumination of the longest hay fed to the steers i s d i f f i c u l t to explain. Duckworth and Shirlaw (1955) found that chopping of long hay increased the duration of rumination cycles as compared with that when the long hay was fed. I t i s possible that the longer length of p a r t i c l e s i n the rumen cause -141- the formation of a l i g h t e r bolus during rumination. Such a bolus would require l e s s comminution than a bolus of the same volume made up of a greater weight of shorter p a r t i c l e s . Unfortunately no research has been done to i n v e s t i g a t e the e f f e c t of d i e t p a r t i c l e s i z e on the p a r t i c l e s i z e and weight of b o l i regurgitated during rumination. The chewing r e s u l t s i n the dairy steer t r i a l support the r e s u l t s of Bae et a l . (1983) who showed that larger animals were more e f f i c i e n t chewers than were smaller animals. In the steer t r i a l , higher metabolic body weight was associated with a s i g n i f i c a n t decrease i n time spent eating and ruminating per kg of feed ingested, and a decrease i n the time spent chewing per bolus regurgitated during rumination. Although the trends were s i m i l a r to those found i n the steer t r i a l , metabolic body weight d i d not have a s i g n i f i c a n t e f f e c t on the chewing behavior i n the dai r y cow t r i a l . The lack of d etection of a s i g n i f i c a n t e f f e c t of body weight may have been due to the experimental design that was used and i t s i n a b i l i t y to completely account f o r a l l the e f f e c t s of animal v a r i a t i o n i n the experiment. The e f f e c t s of higher metabolic body weight on chewing behavior are l i k e l y due to an increased s i z e of the mouth, teeth surface area, esophagus and reticulo-omasal o r i f i c e i n larger animals. Greater prehension p o t e n t i a l , more grinding surface on the teeth, and a larger esophagus would allow a greater rate of intake with a reduced time requirement f o r comminution p r i o r to swallowing. During rumination, due to a larger esophagus, larger animals could regurgitate l a r g e r b o l i which could be more e f f i c i e n t l y reduced i n s i z e by the l a r g e r surface area of the teeth. F i n a l l y , a l a r g e r reticulo-omasal o r i f i c e could pass l a r g e r p a r t i c l e s than those passed i n a smaller animal. This would increase the rate of passage of digesta and decrease the requirement for time spent ruminating per kg of intake i n -142- l a r g e r animals. Bae et a l (1983), however, found that f e c a l p a r t i c l e s i z e d i d not s i g n i f i c a n t l y d i f f e r f o r d i f f e r e n t body sizes i n t h e i r experiments. -143- SUMMARY The present study investigated the e f f e c t of forage median p a r t i c l e length and forage to concentrate r a t i o on the chewing behavior i n dairy c a t t l e . In the f i r s t experiment, l a c t a t i n g dairy c a t t l e were fed orchardgrass hay chopped to two MPLs (7.3 and 18.1 mm) i n two forage to concentrate r a t i o s (40:60 and 60:40) ad l i b i t u m . In the second experiment, dairy steers were fed timothy-brome hay chopped to four MPLs (5.2, 9.0, 13.3 and 20.0 mm) i n a 60:40 forage concentrate r a t i o at 9.5 percent of metabolic body weight. In the dairy cow t r i a l , decreasing the p a r t i c l e length of the forage d i d not s i g n i f i c a n t l y a f f e c t the chewing behavior of the c a t t l e . Increasing the proportion of forage i n the d i e t , however, s i g n i f i c a n t l y increased voluntary feed intake, increased the time spent ruminating and t o t a l time chewing per kg of intake, and increased the number of b o l i regurgitated per kg of intake during rumination. Eating time was not s i g n i f i c a n t l y a f f e c t e d by the proportion of forage i n the r a t i o n . There was also no s i g n i f i c a n t i n t e r a c t i o n between the e f f e c t s of MPL and the proportion of forage i n the r a t i o n on the chewing behavior of the c a t t l e . Decreasing the MPL of the timothy-brome hay fed to the steers s i g n i f i c a n t l y decreased the time the animals spent ruminating and t o t a l time chewing per kg of intake and increased the number of b o l i regurgitated during rumination. There was also evidence that the e f f i c i e n c y of mastication during rumination increased as the MPL of the forage increased. The MPL of the forage d i d not s i g n i f i c a n t l y a f f e c t the time spent eating per kg of intake. There was a d i r e c t r e l a t i o n s h i p between the logarithm of MPL and the chewing behavior of the steers. This r e l a t i o n s h i p suggested that -144- there e x i s t e d a "threshold length" below which the e f f e c t of MPL on chewing behavior becomes s i g n i f i c a n t . Differences i n the metabolic body weight of the steers during the experiment also had a s i g n i f i c a n t e f f e c t on chewing behavior. -145- GENERAL SUMMARY AND CONCLUSIONS The p a r t i c l e s i z e of forages i n ruminant di e t s a f f e c t s the rate of passage of undigested feed p a r t i c l e s from the rumen, the ruminal d i g e s t i b i l i t y of the r a t i o n , and, therefore, the chewing behavior of the animal. However, u n t i l recently, only q u a l i t a t i v e or semi-quantitative methods have been used to characterize the p a r t i c l e s i z e d i s t r i b u t i o n i n processed forage. A method for the quantitation of the p a r t i c l e length d i s t r i b u t i o n i n processed forage was therefore developed, tested, and used to i n v e s t i g a t e the e f f e c t of processing method and forage type on the p a r t i c l e length d i s t r i b u t i o n i n processed forage. The same method was also used to investigate the e f f e c t of forage p a r t i c l e length on voluntary feed intake and chewing behavior i n dairy c a t t l e . A simple v i b r a t i n g tray forage p a r t i c l e separator (FPS) was constructed to separate forage p a r t i c l e s into s i x t h e o r e t i c a l length f r a c t i o n s (<4, 4-10, 10-20, 20-40, 40-80 and >80 mm). The method of a p p l i c a t i o n of forage p a r t i c l e s to the FPS during separation s i g n i f i c a n t l y a f f e c t e d (P < 0.05) the measurement of the p a r t i c l e length d i s t r i b u t i o n . The separation r e s u l t s , however, were repeatable within a given method of a p p l i c a t i o n . When orchardgrass hay, chopped at three t h e o r e t i c a l lengths of cut (TLC: 3.18, 6.35 and 9.53 mm), was separated, only 56.6% of a l l p a r t i c l e s separated (by weight) were c o r r e c t l y c l a s s i f i e d into the above t h e o r e t i c a l p a r t i c l e length f r a t i o n s ; 32.4% were oversized ( c l a s s i f i e d as being longer than they a c t u a l l y were) and 11.0% were undersized ( c l a s s i f i e d as being shorter than they a c t u a l l y were). Based on t h i s degree of over and undersizing, the t h e o r e t i c a l p a r t i c l e length f r a c t i o n s c l a s s i f i e d by the FPS were c a l i b r a t e d to be <3.3, 3.3-8.25, 8.25-16.5, 16.5-33.0, 33.0-66.0 and >66.0 mm. Because -146- the FPS separated p a r t i c l e s on the basis of a s p e c i f i c s i z e parameter, the measurement of forage p a r t i c l e s i z e by t h i s method i s more appropriate than i s the measurement of an u n i d e n t i f i e d p a r t i c l e s i z e parameter using sieving. Separation data f o r the chopped orchardgrass hay, expressed as percent cumulative weight undersize, was f i t t e d by regression to a l i n e a r equation, two exponential equations, a lognormal d i s t r i b u t i o n , and a modified Weibull function. Only the Weibull function adequately f i t the separation data. The c o e f f i c i e n t s of determination f o r the Weibull function were a l l greater than 0.99 and the r e s i d u a l s were randomly d i s t r i b u t e d around the predicted regression l i n e . The median p a r t i c l e length (MPL) could be predicted by the inverse of the B parameter i n the modified Weibull function while the use of the C parameter (named the c o e f f i c i e n t of spread [CS]) as a measure of the spread of p a r t i c l e lengths around a given median was discussed. A l f a l f a and low and high q u a l i t y orchardgrass hays were hammermilled through a 12.7 mm screen and chopped at 3 TLC (3.18, 6.35 and 9.53 mm) and separated on the FPS to determine the dry matter (DM), crude p r o t e i n (CP) and a c i d detergent f i b e r (ADF) MPL and CS of each processed forage. The MPL were based on the weight of each n u t r i e n t c o l l e c t e d i n each p a r t i c l e length f r a c t i o n on the FPS. There was a s i g n i f i c a n t i n t e r a c t i o n (P < 0.05) between the e f f e c t of processing method and forage type on the DM, CP and ADF MPL and CS produced i n the processed forage. Furthermore, the differences i n DM MPL and CS between forages were s i g n i f i c a n t l y d i f f e r e n t (P < 0.05) from those f o r CP and ADF. There were also s i g n i f i c a n t d i f f e r e n c e s (P < 0.05) between the DM and CP MPL, and the DM and ADF MPL, within each forage type. Therefore, d i f f e r e n t forages processed by the same method do not always r e s u l t i n the production of s i m i l a r DM, CP and ADF MPL or CS within or between forage types. Lack of q u a n t i f i c a t i o n of p a r t i c l e s i z e i n research -147- using processed forage may therefore introduce uncontrolled v a r i a t i o n into d i e t a r y treatments. Twelve l a c t a t i n g H o l s t e i n cows were fed orchardgrass hay chopped to two d i f f e r e n t MPL (7.3 and 18.1 mm) at two forage to concentrate r a t i o s (40:60 and 60:40) i n a two by two f a c t o r i a l arrangement i n a two period changeover design. The p a r t i c l e length of the forage d i d not s i g n i f i c a n t l y a f f e c t (P > 0.05) voluntary feed intake (VFI) or chewing behavior. Increasing the forage to concentrate r a t i o i n the d i e t s i g n i f i c a n t l y (P < 0.05) decreased VFI, increased the time spent chewing per kg of feed intake during eating and rumination and increased the number of b o l i regurgitated per kg of feed intake during rumination. Time spent i d l e per kg of feed intake and the time chewing per bolus regurgitated during rumination were not s i g n i f i c a n t l y a f f e c t e d (P > 0.05) by the forage to concentrate r a t i o of the d i e t . There was no s i g n i f i c a n t i n t e r a c t i o n (P > 0.05) between the e f f e c t s of forage MPL and forage to concentrate r a t i o on VFI and chewing behavior. When dairy steers were fed timothy-brome hay chopped to 4 MPL (5.2, 9.0, 13.3 and 20.0 mm) at a 60:40 forage to concentrate r a t i o i n a 4 x 4 L a t i n Square design, increasing the MPL of the forage i n the d i e t s i g n i f i c a n t l y (P < 0.05) decreased the time spent i d l e , increased the time spent ruminating and the t o t a l time spent chewing (eating plus rumination), and increased the number of b o l i regurgitated per kg of feed intake. These e f f e c t s of forage MPL on chewing behavior were shown to be d i r e c t l y r e l a t e d to the logarithm of the forage MPL. Increasing the MPL of the forage from 5.2 or 9.0 mm to 20.0 mm also s i g n i f i c a n t l y decreased (P < 0.05) the time spent chewing per bolus regurgitated during rumination. The MPL of the forage, however, d i d not have a s i g n i f i c a n t e f f e c t on the time spent chewing per kg of feed intake during eating. -148- Body s i z e , included as a covariable i n both dairy c a t t l e t r i a l s , had a s i g n i f i c a n t e f f e c t (P < 0.05) on chewing behavior i n the steer t r i a l , but not i n the dairy cow t r i a l . As body s i z e increased, time spent i d l e increased and the time spent chewing per kg of feed intake, during both eating and rumination, decreased. Larger animals also spent les s time chewing each bolus that was regurgitated during rumination. The differences i n the e f f e c t of forage p a r t i c l e length, and body si z e , on chewing behavior between the two t r i a l s i n d i c a t e d that there may e x i s t a maximum p a r t i c l e length, p o s s i b l y r e l a t e d to body s i z e , below which the e f f e c t of d i e t a r y p a r t i c l e length on the d i g e s t i o n process i n ruminants becomes s i g n i f i c a n t . -149- LITERATURE CITED A l l e n , M.S., J.B. Robertson and P.J. Van Soest. 1984. A comparison of p a r t i c l e s i z e methodologies and s t a t i s t i c a l treatments. In: Techniques i n P a r t i c l e Size Analysis of Feed and Digesta i n Ruminants. (P.M. Kennedy, Ed.). Occ. Pub. 1, Canadian Society of Animal Science, Edmonton, Alberta, Canada: 39-56. ASAE. 1969(a). Method of determining and expressing fineness of feed materials by si e v i n g . Standard ASAE S319. A g r i c u l t u r a l Engineering Yearbook: 346-347. ASAE. 1969(b). 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Res. 8: 424-431. -157- APPENDICES APPENDIX A: PARTITIONING OF THE SUMS OF SQUARES FOR THE ANALYSIS OF INTAKE AND CHEWING BEHAVIOR IN THE DAIRY COW TRIAL (Reduced General Linear Hypothesis Models) (a) T o t a l feed intake: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 8.062 8.062 9.43 0 .015 Length 1 0.036 0.036 0.04 0 .842 % Hay 1 11.056 11.056 12.93 0 .007 Leng x Hay 1 0.003 0.003 0.00 0 .954 Error 19 46.280 2.436 To t a l 34 104.876 Time spent i d l e : Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 596.106 596.106 17.78 0. .001 Length 1 87.440 87.440 2.61 0. .123 % Hay 1 44.038 44.038 1.31 0. .266 Leng x Hay 1 14.680 14.680 0.44 0. .516 Error 19 636.984 33.525 To t a l 23 1379.248 Time spent eating: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 29.260 29.260 ' 4.78 0. .042 Length 1 8.592 8.592 1.40 0, .251 % Hay 1 72.107 72.107 11.77 0. .003 Leng x Hay 1 12.586 12.586 2.05 0. .168 Error 19 116.395 6.126 To t a l 23 238.940 -158- APPENDIX A (cont'd) (d) T o t a l time spent ruminating: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 0.113 0.113 0.01 0. 907 Length 1 13.365 13.365 1.64 0. 215 % Hay 1 100.901 100.901 12.41 0. ,002 Leng x Hay 1 10.283 10.283 1.26 0. ,275 Error 19 154.512 8.132 To t a l 23 279.175 To t a l time spent chewing (eating plus ruminating): Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 33.654 33.654 1.70 0 .208 Length 1 42.560 42.560 2.15 0 .159 % Hay 1 341.562 341.562 17.28 0 .001 Leng x Hay 1 0.086 0.086 0.00 0 .948 Error 19 375.565 19.767 To t a l 23 793.427 Number of b o l i regurgitated: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 1 1.042 1.042 0.08 0 .777 Length 1 26.042 26.042 2.06 0 .167 % Hay 1 165.375 165.375 13.10 0 .002 Leng x Hay 1 9.375 9.375 0.74 0, .400 Error 19 239.792 12.621 Tot a l 23 441.625 -159- APPENDIX A (cont'd) Time chewing per bolus regurgitated: Source Degrees of Freedom Sums of Squares Mean Squares F Value Pr > F Period 1 0. .008 0, .008 4, .16 0. .078 Animal 11 0. .225 0, .020 10, .21 0. .002 Length 1 0. .005 0, .005 2 .72 0. .134 % Hay 1 0. ,000 0. .000 0. .06 0. ,809 Leng x Hay 1 0. ,006 0. .006 2, .96 0, ,124 Error 8 0. ,016 0. .002 To t a l 23 0. ,260 -160- APPENDIX B PARTITIONING OF THE SUMS OF SQUARES FOR THE ANALYSIS OF INTAKE AND CHEWING BEHAVIOR IN THE STEER TRIAL ( F u l l General Linear Hypothesis Models) (a) T o t a l feed intake: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 0.093 0.031 0.65 0 .614 Animal 3 54.287 18.096 383.73 0. .000 Length 3 0.933 0.311 6.59 0, .035 BW0-75 1 0.186 0.186 3.95 0, .104 Error 5 0.236 0.047 To t a l 15 55.734 (b) Time spent i d l e : Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 115.967 38.656 1.58 0. 305 Animal 3 3632.728 1210.910 49.50 0. 000 Length 3 638.998 213.000 8.71 0. 020 BW0-75 1 190.768 124.460 7.80 0. 038 Error 5 122.302 T o t a l 15 4700.762 (c) Time spent eating: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 9.323 3.110 3.06 0. .130 Animal 3 341.094 113.698 112.92 0. .000 Length 3 9.118 3.039 2.99 0, .134 BW0-75 1 5.064 5.064 4.98 0. .076 Error 5 5.079 1.016 To t a l 15 369.679 -161- APPENDIX B (cont'd) (d) T o t a l time spent ruminating: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 42.399 14.133 5.55 0, .048 Animal 3 73.195 24.398 9.57 0. .016 Length 3 131.102 43.700 17.15 0. .005 BW0-75 1 19.095 19.095 7.49 0, .041 Error 5 12.744 2.549 To t a l 15 278.535 To t a l time spent chewing (eating plus ruminating): Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 67.718 22.572 5.43 0 .050 Animal 3 418.917 139.639 33.58 0 .001 Length 3 207.679 69.226 16.65 0 .005 BW0-75 1 44.058 44.058 10.59 0 .023 Error 5 20.793 4.159 To t a l 15 759.165 Number of b o l i regurgitated: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 63.500 21.167 2.92 0. .134 Animal 3 45.500 15.167 2.09 0. ,220 Length 3 334.500 111.500 15.39 0. ,006 BW0-75 1 8.285 8.285 1.14 0. ,334 Error 5 36.214 7.243 Tota l 15 488.000 -162- APPENDIX B (cont'd) Time chewing per bolus regurgitated: Source Degrees of Sums of Mean F Pr > F Freedom Squares Squares Value Period 3 0.005 0.002 1.22 0. .395 Animal 3 0.058 0.019 14.88 0. .006 Length 3 0.025 0.008 6.47 0. .036 BW0-75 1 0.009 0.009 6.80 0, .048 Error 5 0.006 0.001 To t a l 15 0.103 -163-

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