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Forage and concentrate protein utilization by dairy cattle Kamande, George Matiru 1988

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FORAGE AND CONCENTRATE PROTEIN UTILIZATION DAIRY CATTLE. BY GEORGE MATIRU KAMANDE B.Sc. ( A g r . ) , UNIVERSITY OF NAIROBI, 1983. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE-FACULTY OF GRADUATE STUDIES (Department of Animal Science) We a c c e p t t h i s t h e s i s as co n f o r m i n g t o t h e r e q u i r e d s t a n d a r d . THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 198 8, c j George. M a t i r u Kamande 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. Department The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT In the f i r s t part of t h i s study, the r e l a t i v e in s i t u rumen d e g r a d a b i l i t i e s of some common Kenyan feedstuffs were estimated using two f i s t u l a t e d steers. The second part of the study attempted to manipulate rumen fermentation processes by heat treating dietary protein, and also by varying the hay p a r t i c l e s i z e . The in s i t u dacron bag technique was used to estimate the feeding value of some common Kenyan forages. The rate and extent of dry matter (DM) and crude protein (CP) degradation in the rumen was then determined from the incubated samples. E f f e c t i v e DM and CP degradation was also estimated at various rumen digesta flow rates. Green maize chop, fodder sorghum, napier grass, kikuyu grass, Pennisetum trachyphyllum, rhubarb leaves, banana leaves, sweet potato vines, desmodium and lucerne had moderate to high DM and CP degradability (>50%). These feedstuffs would therefore off e r greater p o t e n t i a l for conservation for feeding dairy c a t t l e in the dry season. Wheat straw, maize stover, red oats grass and naivasha stargrass had s i g n i f i c a n t l y (P<0.05) lower rumen degra d a b i l i t y . This l a s t group would require supplemental energy and nitrogen in order to meet the dairy cow's nutrients requirements. Wheat bran had a high DM degradability but i t s CP degradability was low. The d i g e s t i b i l i t y and amino acid a v a i l a b i l i t y of i t s protein i i r e q u i r e s f u r t h e r i n v e s t i g a t i o n s . The e f f e c t s o f f o r a g e p a r t i c l e l e n g t h a n d h e a t t r e a t m e n t of p r o t e i n s o u r c e s on i n t a k e , m i l k y i e l d a n d c o m p o s i t i o n a n d , r a t i o n d i g e s t i b i l i t y w e r e d e t e r m i n e d u s i n g d a i r y c o w s . N o r m a l o r h e a t e d c a n o l a m e a l a n d d e h y d r a t e d a l f a l f a were f e d t o g e t h e r w i t h o r c h a r d g r a s s h a y t o 24 l a c t a t i n g H o l s t e i n c o w s . O r c h a r d g r a s s h a y was c h o p p e d t o two mean c u t l e n g t h s i . e 14 . 19 and 1.71 mm. I n s i t u r e s u l t s showed t h a t b o t h c a n o l a m e a l and a l f a l f a p r o t e i n s i n t h e s u p p l e m e n t was made i n d i g e s t i b l e by h e a t . H e a t t r e a t m e n t d i d n o t a f f e c t i n v i v o d r y m a t t e r (DM), c r u d e p r o t e i n (CP) a n d a c i d d e t e r g e n t f i b r e (ADF) d i g e s t i b i l i t y f o r t h e c o m p l e t e c a n o l a r a t i o n s . M i l k y i e l d was a l s o n o t s i g n i f i c a n t l y a f f e c t e d by h e a t i n g c a n o l a m e a l . H o w e v e r , n e u t r a l d e t e r g e n t f i b r e (NDF) d i g e s t i b i l i t y , v o l u n t a r y f e e d i n t a k e , b u t t e r f a t a n d m i l k p r o t e i n c o n t e n t s d e c r e a s e d w i t h h e a t t r e a t m e n t . R e d u c e d f o r a g e p a r t i c l e s i z e i n c o m b i n a t i o n w i t h h e a t t r e a t m e n t r e s u l t e d i n s i g n i f i c a n t l y l o w e r DM, CP, a n d ADF d i g e s t i b i l i t y . T h e r e was no s i g n i f i c a n t c h a n g e i n v o l u n t a r y f e e d i n t a k e , m i l k y i e l d o r i t s c o m p o n e n t s , ( e x c e p t l a c t o s e c o n t e n t ) , w i t h r e d u c e d hay p a r t i c l e s i z e . L a c t o s e c o n t e n t was s i g n i f i c a n t l y h i g h e r w i t h l o n g c h o p h a y . H e a t t r e a t m e n t o f " a l f a l f a a n d s h o r t h a y p a r t i c l e s i z e r e s u l t e d i n l o w e r DM a n d CP d i g e s t i b i l i t y o f t h e c o m p l e t e r a t i o n s . ADF d i g e s t i b i l i t y a n d v o l u n t a r y f e e d i n t a k e were i i i reduced with heat treatment. Hay p a r t i c l e s i z e d i d not a f f e c t v o l u n t a r y feed intake s i g n i f i c a n t l y . M i l k y i e l d and i t s components i n c r e a s e d with heat treatment of a l f a l f a . Only t o t a l milk f a t i n c r e a s e d with the longer chop hay. i v TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS v LIST OF TABLES v i LIST OF FIGURES v i i i LIST OF APPENDIX TABLES i x ACKNOWLEDGEMENT X CHAPTER ONE: E v a l u a t i o n of some Kenyan forages u s i n g the Nylon bag t e c h n i q u e . I n t r o d u c t i o n 1 L i t e r a t u r e review 4 M a t e r i a l s and methods 23 R e s u l t s 26 D i s c u s s i o n 41 Summary and c o n c l u s i o n s 46 CHAPTER TWO: To determine the e f f e c t of forage p a r t i c l e l e n g t h and heat treatment of p r o t e i n sources on i n t a k e , m i l k y i e l d and composition and r a t i o n d i g e s t i b i l i t y i n d a i r y c a t t l e . I n t r o d u c t i o n 49 L i t e r a t u r e review 51 M a t e r i a l s and methods 69 R e s u l t s 72 D i s c u s s i o n 88 Summary and c o n c l u s i o n s 98 General Summary 100 LITERATURE CITED 103 APPENDICES 112 V LIST OF TABLES Page Table 1 Names and stage of harvesting the forage samples.25 Table 2 Chemical composition of forage samples 27 Table 3 Dry matter degradation constants 30 Table 4 Crude protein degradation constants 31 Table 5 Ef f e c t i v e dry matter degradation 32 Table 6 Ef f e c t i v e crude protein degradability 33 Table 7 Composition of the ration feedstuffs 72 Table 8 Mean extent on DM and CP degradation over the experimental duration - i n s i t u 73 Table 9 Mean extent of DM and CP degradation for canola and a l f a l f a based concentrates - i n s i t u ..73 Table 10 Degradation rate constants of canola and a l f a l f a concentrates .78 Table 11 D i g e s t i b i l i t y and da i l y feed intake of canola based rations over the experimental duration 81 Table 12 Dry matter and crude protein d i g e s t i b i l i t y c o e f f i c i e n t s of canola based rations 81 Table 13 Daily feed intake of canola treatments 81 Table 14 Milk y i e l d and composition over the experimental duration -canola based rations 82 v i Table 15 E f f e c t s of canola r a t i o n treatments on milk y i e l d and composition 82 Table 16 D i g e s t i b i l i t y of a l f a l f a based r a t i o n s ...82 Table 17 Dry matter and crude p r o t e i n d i g e s t i b i l i t y of a l f a l f a treatments 83 Table 18 D a i l y feed intake and ADF d i g e s t i b i l i t y 83 Table 19 M i l k y i e l d and composition f o r a l f a l f a treatments 83 Table 20 M i l k y i e l d and composition of a l f a l f a treatments 84 v i i LIST OF FIGURES F i g u r e 1 % Degradation versus incubation time -Green maize chop 29 F i g u r e 2 % Degradation versus incubation time -Kikuyu grass 36 F i g u r e 3 % Degradation versus incubation time -Lucerne (LB) 37 F i g u r e 4 % Degradation versus incubation time -Rhubarb leaves 38 F i g u r e 5 % Degradation versus incubation time -Canola concentrates [DM] 74 F i g u r e 6 % Degradation versus incubation time -Canola concentrates [CP] 75 F i g u r e 7 % Degradation versus incubation time - A l f a l f a concentrates [DM] 76 F i g u r e 8 % Degradation versus incubation time - A l f a l f a concentrates [CP] 77 LIST OF APPENDIX TABLES Appendix 1 Composition of the d a i r y r a t i o n s f ormulated .112 Appendix 2 Exp e r i m e n t a l layout i n the t r i a l 113 ix ACKNOWLEDGEMENTS My sincere gratitude goes to my research supervisor, Dr J.A. Shelford, Associate Professor, Animal Science Department. "Your unfaltering support, guidance, encouragement and constructive c r i t i c i s m s throughout the various aspects of thi s work remains c l e a r l y unmatched". 1 am also g r a t e f u l to; Professor B.D. Owen, Animal Science Department and Dr L.J. Fisher, Research S c i e n t i s t , Agriculture Canada, Agassiz, the two other members of my graduate committee. Their advice and encouragement in the preparation and writing of t h i s thesis was immeasurable. My gratitude also goes to the Kenya Government and Canadian International Development Agency (C.I.D.A.) for awarding the scholarship that made t h i s study possible. Special thanks go to the South Campus s t a f f and a l l the technicians in the Animal Science laboratory for their assistance. F i n a l l y , 1 would l i k e to dedicate t h i s thesis to my family and a l l my friends, r e a l l y wonderful people. CHAPTER 1 EVALUATION OF SOME KENYAN FORAGES USING THE DACRON-BAG TECHNIQUE. INTRODUCTION One of the major f a c t o r s l i m i t i n g the e x p l o i t a t i o n of l i v e s t o c k p r o d u c t i o n p o t e n t i a l i n Kenya r e l a t e s to the s e a s o n a l i t y of forage p r o d u c t i o n . The uneven d i s t r i b u t i o n of r a i n f a l l throughout the year i s the main cause of t h i s . Although g r a i n f e e d i n g p r o v i d e s the hig h n u t r i e n t d e n s i t y r e q u i r e d f o r e x p l o i t a t i o n of the g e n e t i c p o t e n t i a l of the d a i r y cow, p r o d u c t i o n c o s t s are h i g h . A l s o , d a i r y cows r e q u i r e forages to remain h e a l t h y . Fodder crops are u s u a l l y more c o s t e f f e c t i v e . I t i s t y p i c a l t h a t growth of fodder crops i s very r a p i d j u s t a f t e r the onset of the r a i n s and t r a i l s o f f to l i t t l e or no growth at a l l , at the height of the dry season. I n t e n s i v e milk p r o d u c t i o n r e q u i r e s an even supply of feeds throughout the year. The n u t r i t i v e value of most f e e d s t u f f s f a l l s r a p i d l y as the forage matures. T h i s r e s u l t s i n a p a t t e r n of r a p i d l i v e w e i g h t gains i n the e a r l y wet season, slower but s t i l l s u b s t a n t i a l gains u n t i l some time a f t e r the end of the short r a i n s , then l o s s e s i n the dry season and e a r l y r a i n y season. Reduced milk y i e l d s are a l s o observed i n the dry season. To overcome t h i s management problem, farmers have to e i t h e r preserve the forage s u r p l u s d u r i n g the r a i n y season, i n the form of hay or s i l a g e or feed . . 1 concentrates. Other p o s s i b i l i t i e s l i k e the adjustment of stocking rates over the seasons may not be f e a s i b l e in a smallholder dairy set-up, in view of the imperfect nature of the breeding stock market. Regulating the seasonality of forage production through i r r i g a t i o n may not be economically viable for the majority of smallholders because of the high costs involved. The in s i t u dacron bag technique could be used to estimate the potential feeding value of forages (Orskov e_t a l . , 1980). Information on the d e g r a d a b i l i t i e s of d i f f e r e n t forages, of the v a r i a t i o n between species and v a r i e t i e s , of the differences between parts of the plant and the effect of maturity on degradability, result in a better understanding of the potential value of the forages and t h e i r selection in dairy rations. It i s acknowledged (Orskov et a l . , 1980) that l i t t l e i s known of the r e l a t i v e degradability of the wide range of t r o p i c a l forages and browses available or p o t e n t i a l l y a v a i l a b l e . A great deal of information on forages i s therefore required. Accumulation of t h i s type of information w i l l ensure that feedstuffs are a l l o c a t e d on the basis of their degradation rates, pot e n t i a l degradability and outflow rate from the rumen with a given type of d i e t . Rumen degradation as measured by the nylon bag technique refers to the breakdown of material to a size small enough to leave the bag and not necessarily a complete degradation to simple chemical compounds. A feedstuff with low and slow . .2 degradability could result in reduced voluntary feed intake and thus l i m i t the performance of the animal. The s i m p l i c i t y and d i r e c t relevance to the value of the feed material under investigation make the dacron bag technique a useful tool in exploring the feeding value of common Kenyan feedstuffs. An attempt w i l l be made in t h i s t r i a l to evaluate and make suggestions on the feedstuffs with a pot e n t i a l for conservation in view of the i r superior degradation c h a r a c t e r i s t i c s . These feed materials w i l l presumably help even out the feed supplies across the seasons. Evaluation w i l l also be done and comparisons made on al t e r n a t i v e crop residues a v a i l a b l e . It i s anticipated that possible combinations of feedstuffs useable in dairy rations w i l l be i d e n t i f i e d . Proper selection of ration ingredients i s important in avoiding possible depressions in d i g e s t i b i l i t y and hence available supplies of energy and amino acids. The present study was therefore undertaken with the following object ives: a) To determine the rate and extent of rumen degradation of some common Kenyan feedstuffs. b) To i d e n t i f y possible combinations of the feedstuffs to include in a dairy cow rat i o n . . .3 LITERATURE REVIEW GROWTH PATTERN OF FORAGES. Background Information. The smallholder dairy production is mainly located in the Kenyan Highlands, at an elevation of 1500 to 2,000m above sea l e v e l and receives 700 to 2,000mm of rain per year (Stotz, 1983). There are about 1.5 m i l l i o n smallholder livestock farms occupying approximately 3.5 m i l l i o n hectares (ha) of farm land, the majority of which are less than 2 ha (Odingo, 1971). The importance of smallholder livestock farming i s shown by the fact that they represent over 50% of the national livestock herd. In 1981, 75% and 65% of the t o t a l national milk and beef output came from smallholders (Stotz, 1983). Smallholder livestock farming also provides gainful employment to a large number of Kenyans. Forage from smallholdings i s drawn from permanent pastures, grass leys, arable fodder crops and food crop residues. Under leys and permanent pastures naturally occurring grass species such as kikuyu grass (Pennisetum clandestinum), stargrass (Cynodon dactylon), nandi set a r i a (Setaria sphacelata) and rhodes grass (Chloris gayana) predominate, napier grass (Pennisetum purpureum), fodder sorghum (Sorghum sudanense), lucerne (Medicago sativa) are the common fodder crops. Food crop residues include maize . .4 stover (Zea mays), banana leaves (Musa spp.) and sweet potato vines (Ipomoea batatas) among others. Environmental e f f e c t s on forage q u a l i t y . A prerequisite for making more e f f i c i e n t use of forages is knowing their value, as sources of protein and energy, at thei r d i f f e r e n t stages of development. Thereafter comes the question of feeding the best avai l a b l e supplements. Forage quality normally involves considerations on the productive capacity of forages as major dietary ingredients and also the optimum time to harvest for conservation. At harvest time, forages r e f l e c t the cumulative result of plant growth and the environmental factors influencing the d i s t r i b u t i o n of photosynthetically derived energy and nutrients in the plant (Van Soest et a l . , 1978). Environmental conditions of growth determine the plants composition which in turn controls the l i m i t s of n u t r i t i v e value. Reviewing l i t e r a t u r e on the n u t r i t i o n a l value of t r o p i c a l grasses, French (1957) concluded that at the stage of maximum energy y i e l d , they are higher in f i b r e and l i g n i n and lower in protein and phosphorus. They also suffer more desiccation losses of leaves in s i t u and are less d i g e s t i b l e than temperate grasses. Butterworth (1967) compiled and tabulated a large.number of data on chemical composition and d i g e s t i b i l i t y of t r o p i c a l grasses from d i f f e r e n t parts of the world. . .5 The interaction of high temperature, a c h a r a c t e r i s t i c of Kenyas dry season, with pasture quality has received some attention. Working with some t r o p i c a l grass species, Deinum and Dirven (1975) found that the poor q u a l i t y a t t r i b u t e of t r o p i c a l grasses i s mainly due to the high temperature in the i r e c o l o g i c a l niche, and also to the large negative e f f e c t s of age and stem formation. Wilson and Minson (1983) indicated that grasses decrease by an average of 0.006 units of d i g e s t i b i l i t y for each 1°C increase in temperature over the normal growth range. The reduction in d i g e s t i b i l i t y of t r o p i c a l legumes was found to be much smaller with average decreases of 0.0028 units of d i g e s t i b i l i t y per 1*C increase. Increased temperature was associated with an increase in c e l l wall contents and l i g n i n contents. The t o t a l non-structural carbohydrate content of herbage decreases with higher growth temperatures (Wilson and Minson, 1983). It i s generally observed that the factors that retard plant development e.g water stress and cold environmental temperatures also promote the maintenance of forage q u a l i t y (Van Soest et a l . , 1978). Forage also declines in n u t r i t i v e value with increasing age as i s explained in the subsequent chapter. Wilson and Minson (1983) however observed that high temperatures have greater detrimental e f f e c t s on older tissue dry matter than ._on younger tis s u e s . Some experiments on the d i g e s t i b i l i t y of Kenyan grasses have been c a r r i e d out (Laksesvela and Said, 1978; Said, 1971; . .6 Van A r k e l et a l . , 1977). The g e n e r a l view as summarized by L a k s e s v e l a and S a i d (1978) was t h a t : P r o t e i n i s h i g h l y e x c e s s i v e i n the best e.g Kikuyu g r a s s , but more s e r i o u s l y d e f i c i e n t i n poor pasture e s p e c i a l l y f o r d a i r y cows. Energy was a l s o found to be d e f i c i e n t i n a l l p a s t u r e s f o r medium or h i g h producing d a i r y cows. T h i s adverse n u t r i t i o n a l s i t u a t i o n d e t e r i o r a t e s as the forages mature. C l e a r l y , t h i s demonstrates the c r i t i c a l need f o r c o r r e c t supplementation ' and forage management. RUMEN DEGRADABILITY OF DIETARY PROTEIN. Rumen microflora. D i e t a r y p r o t e i n e n t e r i n g the rumen i s r a p i d l y degraded by potent rumen m i c r o b i a l p r o t e a s e s and deaminases (Chalupa, 1975; S e t a l a , 1983). P r o t e o l y t i c a c t i v i t y o ccurs i n at l e a s t B a c i l l u s s p e c i e s , B a c t e r o i d e s , B u t y r i v i b r i o , Selenomonas, C l o s t r i d i u m and, one s t r a i n of S t r e p t o c o c c u s ( R u s s e l l and H e s p e l l , 1981). Most of the m i c r o b i a l p r o t e o l y t i c enzymes are c e l l bound but are l o c a t e d on the c e l l s u r f a c e to p r o v i d e f r e e access to s u b s t r a t e and are comprised of both exo- and endopeptidase (Chalupa, 1975). P r o t e o l y s i s i n the rumen i s an a c t i v e process and appears to be more of a f u n c t i o n of m i c r o b i a l c e l l biomass than of content of p r o t e i n or other c o n s t i t u e n t s i n the d i e t . During p r o t e o l y s i s most p r o t e i n s are broken down to p e p t i d e s , amino a c i d s and f i n a l l y to ammonia and carbon c h a i n s (Chalupa, 1975). U n l i k e p r o t e o l y s i s , deamination . .7 a c t i v i t y i s d i r e c t l y r e l a t e d to d i e t a r y p r o t e i n content (Lewis, 1955). Amino a c i d deamination c a p a c i t y g e n e r a l l y exceeds the r a t e of amino a c i d r e l e a s e by p r o t e o l y s i s . T h i s i s demonstrated by the f a c t t h a t amino a c i d s accumulate only t r a n s i e n t l y , even when l a r g e amounts of very d i g e s t i b l e p r o t e i n s are i n t r o d u c e d i n t o the the rumen (Lewis, 1962). P r o t e o l y s i s i s t h e r e f o r e thought to be the st e p l i m i t i n g ruminal d e g r a d a t i o n of p r o t e i n s . Work by Nugent and Mangan (1981) showed that the p r o t e o l y t i c a c t i v i t y i n the rumen i s almost e n t i r e l y a s s o c i a t e d w i t h b a c t e r i a l c e l l s and that c e l l - f r e e rumen f l u i d and protozoa have l i t t l e a c t i v i t y . P r o t o z o a l p r o t e o l y s i s takes p l a c e by i n g e s t i o n of smal l feed p a r t i c l e s and b a c t e r i a , with s u r p l u s amino a c i d s being e x c r e t e d back i n t o the surrounding medium (Tamminga and Hellemond, 1977). These f r e e amino a c i d s are then u t i l i z e d or degraded by b a c t e r i a . Entodinium lonqinucleatum and P o l y p l a s t r o n m u l t i v e s i c u l a t u r n are amongst the few protozoa t h a t can i n c o r p o r a t e f r e e amino a c i d s ( S e t a l a , 1983). Ammonia a s s i m i l a t i o n by rumen b a c t e r i a takes p l a c e through amination and t r a n s a m i n a t i o n mechanisms. These mechanisms are thought to g i v e r i s e to about 50 to 70% of the t o t a l m i c r o b i a l n i t r o g e n a s s i m i l a t e d (Mathison and M i l l i g a n , 1971). Ammonia c o n c e n t r a t i o n of about 3-8 mg per cent i n the rumen f l u i d i s s u f f i c i e n t f o r optimum s y n t h e s i s of b a c t e r i a l p r o t e i n (Kaufmann and Lupping, 1982). However, with the commercial d i e t s normally used on the farms, the supply of . .8 ammonia, and also amino acids and peptides i s more than adequate in meeting the requirements of the bacteria (Hagemeister et a l . , 1980). Besides ammonia, some rumen bacteria also require branched-chain fatty acids, peptides and amino acids for the synthesis of microbial protein (Chalupa, 1975). Methionine and cysteine are some of the amino acids thought to be stimulatory to certain strains of bacteria (Orskov, 1982; Chalupa, 1975; Kaufmann and Lupping, 1982). Supplementation of a l l non-protein nitrogen (NPN) diets with s p e c i f i c amino acid carbon-chains has increased nitrogen (N) retention in growing sheep (Broderick, 1975), and ruminal microbial protein synthesis (Hume, 1970). Though Setala (1983) acknowledges sit u a t i o n s where urea prevented the degradation of feed protein, Chalupa (1975) noted otherwise. Ruminal protozoa obtain most of t h e i r protein requirements by engulfment of bacteria but have amino acid requirements similar to those of higher animals (Hungate, 1966). Therefore, intact proteins or amino acids may have an e f f e c t through stimulation of protozoal growth. Patton et a l ., (1970) observed s i g n i f i c a n t increase in ruminal protozoal numbers afte r supplementing sheep with methionine and i t s hydroxy analogue. Implications from the above considerations point to the fact that t o t a l protection of dietary proteins from ruminal degradation may result in reduced supply of e s s e n t i a l non-ammonia factors normally derived from protein fermentation. . .9 The u t i l i z a t i o n of products of proteolysis i s greatly dependent on the amount of energy available to the microbes in the rumen. Carbohydrates are thought to be superior to proteins as energy sources for microbial protein biosynthesis (Tamminga, 1979). A need therefore arises to balance the degradation rate of feed protein and the release of energy from the feeds. In extreme cases of imbalance, uncoupled fermentation, i n f e r t i l i t y problems or even ammonia t o x i c i t y may result (Setala, 1983). The extent to which the microbial protein meets the animals t o t a l protein requirements and i t s amino ac i d p r o f i l e , determines i t s s i g n i f i c a n c e . FACTORS AFFECTING PROTEIN DEGRADABILITY IN THE RUMEN. The va r i a t i o n in d e g r a d a b i l i t i e s between feeds have been observed by many workers (Satter, 1986; Zinn et a l . , 1981; Siddons and Paradine, 1981). Amino acids absorbed from the ruminants small intestines have their o r i g i n in the rumen microbes, undegraded dietary protein, and endogenous protein. Microbial protein supplies approximately two-thirds of the l a c t a t i n g cows amino acids requirements, and dietary protein accounts for most of the remainder (Satter, 1986). Hence, the animal performance i s greatly influenced by the quantity of protein degraded in the rumen. Numerous factors influence ruminal degradation by a l t e r i n g microbial a c t i v i t y and access to the protein. Among the factors involved include the extent of c r o s s l i n k i n g in the protein ( d i s u l f i d e bonds), retention time in the rumen, ..10 p r o t e i n s o l u b i l i t y , p r o t e i n i n t a k e and, p r o c e s s i n g and storage e f f e c t s on p r o t e i n ( C l a r k , 1975; Chalupa, 1975; S a t t e r , 1986). Other c h a r a c t e r i s t i c s of the p r o t e i n i t s e l f and feed p a r t i c l e i n which the p r o t e i n r e s i d e s are a l s o i n f l u e n t i a l . Mahadevan et a l . , (1980) showed that many p r o t e i n s (both s o l u b l e and i n s o l u b l e ) that were r e s i s t a n t to de g r a d a t i o n became e a s i l y degradable a f t e r treatment with mercaptoethanol or p e r f o r m i c a c i d . Mercaptoethanol and pe r f o r m i c a c i d treatments have the s p e c i f i c e f f e c t s of brea k i n g the d i s u l f i d e bonds i n p r o t e i n s . P r o t e i n s with e x t e n s i v e c r o s s l i n k i n g e.g with d i s u l f i d e bonds are l e s s a c c e s s i b l e to p r o t e o l y t i c enzymes and are t h e r e f o r e r e l a t i v e l y r e s i s t a n t to de g r a d a t i o n ( S a t t e r , 1986). P r o t e i n s i n h a i r and f e a t h e r s are examples of h i g h l y c r o s s l i n k e d p r o t e i n s . Many chemical treatments have been used to make the feed p r o t e i n s r e s i s t a n t to d e g r a d a t i o n i n the rumen. Treatment of p r o t e i n s with formaldehyde causes methylene c r o s s l i n k i n g , thus re d u c i n g the r a t e of p r o t e o l y s i s ( S a t t e r , 1986). The p o s s i b i l i t y of i n t r o d u c i n g d i s u l f i d e bonds i n the p r o t e i n s has not been t e s t e d (Mahadevan et a l . , 1980). Ovalbumin i s a s o l u b l e but c y c l i c p r o t e i n having no t e r m i n a l amino a c i d or c a r b o x y l group. The c y c l i c f e a t u r e reduces the ra t e of p r o t e o l y s i s ( S a t t e r , 1986). T h i s demonstrates the i n f l u e n c e of the t e r t i a r y s t r u c t u r e on p r o t e i n s o l u b i l i t y . Wohlt et a l . , (1973) r e p o r t e d that p r o t e i n s o l u b i l i t y i s . . 1 1 higher in feeds containing more albumins and globulins than prolamins and g l u t e l i n s as a major protein f r a c t i o n . A high s o l u b i l i t y often means a rapid degradation of feed protein in the rumen (Crawford et a l . , 1978). Access to protein by proteases i s greater when protein i s in s o l u t i o n . The maturity of plants at harvest a f f e c t s the type of protein present in the t o t a l plant and t h i s influences s o l u b i l i t y of the plant protein (Waldo, 1968). As forages increase in maturity, the protein f r a c t i o n s , albumin, globulin, prolamin and g l u t e l i n decrease and the nonprotein nitrogen (NPN) content increases (Clark, 1975). Clark further adds that the soluble nitrogen content of forage i s greatest at maturity except for cereal grains. Soluble proteins d i f f e r greatly in the rate at which they are hydrolyzed. Soluble feed proteins from soybean meal and rapeseed meal were hydrolyzed at about one-fourth the rate of hydrolysis of casein (Mahadevan et a l . , 1980). Results from various studies (Pichard and Van Soest, 1977; Crawford et a l . , 1978; Mahadevan et a l . , 1980) show that in v i t r o determination of protein s o l u b i l i t y may not be a good measure of the degradability of feed proteins. It i s reasonable to expect protein s o l u b i l i t y to predict differences in protein degradation more accurately when applied to a group of similar feeds than when used across a diverse group of feeds d i f f e r i n g in physical and chemical propert i e s . Factors that regulate the rate of flow of feed . . 12 ingredients through the rumen influences the extent of ruminal degradation. A shorter retention time in the rumen allows less time for microbial fermentation. In addition, an increased passage rate of undigested forage residue out of the rumen may be associated with increased feed intake and depressed d i g e s t i b i l i t y (Hartnell and Satter, 1979). Clark (1975) reported that reducing p a r t i c l e size of the d i e t , increasing dietary feed intake, increased frequency of feeding, and rate of ruminal degradation w i l l increase the rate of passage of digesta through the rumen. High producing ruminants consuming large quantities of feed are l i k e l y to have a smaller f r a c t i o n of dietary protein degraded in the rumen than animals consuming low or moderate amounts. Tamminga (1979) working with cows consuming 8.2 or 12.9 Kg of dry matter d a i l y reported 29 and 45 percent undegraded dietary protein as a percent of t o t a l dietary protein. Using samarium sprayed hay p a r t i c l e s of d i f f e r e n t s i z e s , Hartnell and Satter (1979) found the eff e c t of the l e v e l of intake on turnover rates, to be i n s i g n i f i c a n t . Hence the impact on protein degradation from increased passage may also be minor or without e f f e c t (Satter, 1986; McAllan and Smith, 1983; M i l l e r , 1973). Rumen d i l u t i o n rate was defined as the proportion of t o t a l rumen volume leaving the rumen per hour (Harrison et a l . , 1975). Some work quoted by these researchers found that the y i e l d of bacteria dry matter per mole of ATP derived from ..13 rumen fermentation could be a l t e r e d by varying the d i l u t i o n rate. Increasing the d i l u t i o n rate of rumen f l u i d can increase the flow of protein from the rumen of sheep and steers (Satter, 1986). This increase i s a t t r i b u t e d to a net increase in e f f i c i e n c y of microbial synthesis (Stokes et a l ., 1985) and partly due to an increase in the proportion of undegraded dietary protein (Satter, 1986). Rumen f l u i d d i l u t i o n rates have been increased by high feed intakes, inclusion of sodium s a l t s (Stokes et a l . , 1985) and, infusion of s a l i v a (Harrison et a l . , 1975). Another factor that may influence passage rate and hence the ruminal degradation i s the c a l o r i c demand. Kennedy e_t a l . (1976) reported that sheep challenged with an increased c a l o r i c demand as a re s u l t of cold exposure had an increased rate of digesta passage. This increased the amount of microbial crude protein and the amount of undegraded dietary protein. It i s conceivable that in early l a c t a t i o n , when the cow i s mobilizing body tissu e to supply c a l o r i e s , that increased rate of digesta passage w i l l r e s u l t . Hartnell and Satter (1979) did not however observe s i g n i f i c a n t change in passage rate over the l a c t a t i o n period. Rumen pH i s normally between 5.5 and 7.0 (Hungate, 1966). Lower rumen pH, which usually accompanies increased feed intake, may reduce b a c t e r i a l and p r o t e o l y t i c a c t i v i t y . Proteins with an i s o e l e c t r i c point in the normal rumen pH range would then have reduced s o l u b i l i t y (Satter, 1986) and ..14 possibly a l t e r e d protein degradability also. Feed processing methods such as p e l l e t i n g , extrusion, and steam r o l l i n g and f l a k i n g may generate enough heat to a l t e r protein and either increase or decrease ruminal degradation of proteins. Disruption of the protein matrix may result in increased ruminal degradation, whereas heat applied or generated during grain processing can achieve the opposite (Chalupa, 1975). Some processing procedures increase microbial protein production by increasing the quantity of starch fermented in the rumen. Relationships worked out by Satter (1986) show that as heat input to a feed i s increased, the amount of undegraded protein increases. THE NYLON BAG TECHNIQUE AND RUMINAL PROTEIN DEGRADATION. In many in v i t r o and in s i t u experiments, protein degradation has been described as a function of time (Weakley et a l . , 1983; Orskov and McDonald, 1970; Lindberg, 1984). The extent of degradation determines both the degradable part av a i l a b l e for the rumen microbes and the undegraded protein which may be available for host animal enzymic digestion. Two methods of obtaining quantitative estimates of degradability are used, namely, measuring the quantity of dietary protein entering the abomasum (De Boer et a l . , 1986; Orskov, 1980), or by incubating dietary protein in nylon bags in the rumen for fixed durations (Orskov and McDonald, 1970; Orskov et a l . , 1980)w The f i r s t method involves the d i f f i c u l t i e s of maintaining s u r g i c a l l y prepared animals, ..15 r e q u i r e s lengthy s e r i e s of a n a l y s e s , and i s s u b j e c t to u n c e r t a i n t y as to the a c c u r a t e s e p a r a t i o n of m i c r o b i a l and d i e t a r y p r o t e i n . The nylon-bag (dacron bag, a r t i f i c i a l f i b r e bag, rumen bag) technique d e s c r i b e d by Orskov et a l . (1980) p r o v i d e s u s e f u l i n f o r m a t i o n on both the extent and r a t e of d e g r a d a t i o n . Most data on p r o t e i n d e g r a d a t i o n f i t s a g e n e r a l model with three p r o t e i n p o o l s ( S a t t e r , 1986): Pool A, non p r o t e i n n i t r o g e n or p r o t e i n that i s degraded very r a p i d l y . Pool B, p r o t e i n degraded at a r a t e s i m i l a r to the f r a c t i o n a l r a t e of d i g e s t a passage from the r e t i c u l o r u m e n (approximately 0.02 to 0.2 per hour). Pool C, bound or u n a v a i l a b l e p r o t e i n degraded very slowly or not at a l l . I d e a l l y , each pool has a degradation r a t e that i s assumed f r a c t i o n a l , t h a t i s , a constant p r o p o r t i o n of the remaining p r o t e i n i s degraded per u n i t of time. A l s o , o n l y d e g r a d a t i o n of p o o l B p r o t e i n w i l l be a f f e c t e d by the r e l a t i v e r a t e of passage. V a r i o u s techniques e x i s t t h a t p r o v i d e reasonable e s t i m a t e s of the d i f f e r e n t pools and the r e l e v a n t f r a c t i o n a l r a t e c o n s t a n t s . Orskov (1982) and Faichney (1975) reviewed the use of markers to the flow of d i g e s t a at given p o i n t s i n the r e t i c u l o r u m e n and can p r o v i d e u s e f u l e s t i m a t e s of v a r i o u s c o n s t a n t s . P i c h a r d and Van Soest (1977) used Streptomyces g r i s e u s protease and found that i n s o l u b l e p r o t e i n s of some forages i n c l u d e a r a p i d l y degradable f r a c t i o n and a more slowly degradable f r a c t i o n . Feeds t h e r e f o r e seem to c o n t a i n ..16 several types of protein that are in the B f r a c t i o n , and presumably each protein has i t s own f r a c t i o n a l degradation rate. The d i f f i c u l t i e s of measuring the f r a c t i o n a l rates in pool B are quite evident. E x i s t i n g procedures including that described by Orskov et a l . (1980) f a i l to sort out individual rate constants but do y i e l d an average rate. The percentage of material degraded 'P' a f t e r a time ' t ' hours may be described by the equation; P = a + b(1 - e~ c t) (i) [Orskov et a l . , 1980]. where, P = the actual degradation af t e r time ' t ' , t = the incubation time in hours, a = the intercept of the degradation curve at time zero, b = the potential degradability of the component that w i l l , in time, be degraded. c = the rate constant for the degradation of 'b' (%/hr). Pool A, as measured by t h i s technique, consists of soluble proteins and proteins residing in very small p a r t i c l e s that are removed when the bag i s incubated and/or washed for 1 hour (Satter, 1986). Mahadevan et a l . (1980) working with the protease in Bacteroides amylophilus found that soluble protein from f i s h meal was hydrolyzed at about double the rate of hydrolysis of soluble proteins from soybean meal or rapeseed meal. These results point to the fact that, not a l l soluble proteins are degraded in the rumen and vice versa. . . 17 Only the d e g r a d a t i o n of p o o l B p r o t e i n i s a f f e c t e d by the r e l a t i v e r a t e of passage. T h e r e f o r e e f f e c t i v e d e g r a d a b i l i t y ( p e f f ) i s ; P f f = a + bc/(c + k) ( i i ) [Orskov et a l . , 1980] where, a,b and c are given i n equation ( i ) above, and k = r e l a t i v e r a t e of passage of pool B. Since the t o t a l d e g r a d a b i l i t y of the sample i s given by (a+b), then l00-(a+b) r e p r e s e n t s the f r a c t i o n which w i l l appear to be undegradable in the rumen. The i n s i t u bag technique has many shortcomings and i s s u b j e c t to a number of v a r i a b l e s (Orskov et a l . , 1980; Weakley et a l . , 1983): The sample i s not exposed to any breakdown due to chewing and rumination s i n c e i t i s c o n f i n e d w i t h i n the bag. Measurements o b t a i n e d t h e r e f o r e , are f o r the breakdown of a sample to a s i z e small enough to leave the bag and not n e c e s s a r i l y a complete deg r a d a t i o n to simple chemical compounds. Normally the s u i t a b l y broken down feed p a r t i c l e s would be a b l e to leave the rumen. E x t e n s i v e s t u d i e s on; bag pore s i z e , sample weight, bag s u r f a c e area r a t i o , s u b s t r a t e p a r t i c l e s i z e and, animal d i e t e f f e c t s have been c a r r i e d out to determine t h e i r i n f l u e n c e on in s i t u degradation measurements (Orskov et a l . , 1980; S e t a l a , 1983; Weakley et a l . , 1983). V a r i a b i l i t y due to washing technique was r e c o g n i z e d by Weakley et a l . (1983) and r e c e n t l y De-Boer et a l . (1986) d e s c r i b e d a m o d i f i e d and more . . 18 consistent method. Uden et a l • (1974) observed a reduction in substrate disappearance as a result of decreasing bag pore s i z e . Greater d i g e s t i b i l i t y of Guinea grass from nylon bags with a 53-nm pore size was observed as compared to 20- or 35-nm porosity bags. Weakley et a l . (1983) observed a greater disappearance of dry matter and nitrogen from soybean meal and d i s t i l l e r s grains with dacron (52-nm pore size) than from rip-stop nylon bags (no v i s i b l e pores). These differences are deemed to have been due to larger porosity materials allowing greater efflux of digested residues. Other researchers (Uden et a l . , 1974; Nocek et a l . , 1979) have observed gas accumulation in bags with pore sizes ranging from 20- to 35nm, resulting in limited d i g e s t i b i l i t y in s i t u . The d i f f e r e n t i a l pressures and tumbling fibrous mat may be required to remove obstructions, such as the par t i c u l a t e matter or b a c t e r i a l slime, from the pores of small pore bag materials, and thus preventing gas accumulation within the bag (Weakley et a l . , 1983). The optimum size of bag i s determined by the necessity to have the bag large enough r e l a t i v e to the sample size used. This ensures that rumen f l u i d can e a s i l y enter the bag and mix with the sample (Orskov et a l . , 1980). Also, the bag need be small enough, to be e a s i l y withdrawn through the rumen cannula. Ideally the sample prepared for incubation should . . 19 r e p r e s e n t the m a t e r i a l s as they would appear in the rumen a f t e r i n g e s t i o n by the animal. M a s t i c a t e d i n g e s t a from oesophageal cannula, hammermilling through 2.5 to 3.0 mm s c r e e n , chopping, c u t t i n g , r o l l i n g and g r i n d i n g are u s u a l l y used to reduce the s u b s t r a t e p a r t i c l e s i z e . Decreasing p a r t i c l e s i z e would be expected to i n c r e a s e s u r f a c e area per u n i t weight of s u b s t r a t e , thus i n c r e a s i n g exposure of the s u b s t r a t e to m i c r o b i a l a t t a c k i n s i t u . However Weakley et a l . (1983) i n d i c a t e s t h a t clumping of p a r t i c l e s l e s s than 0.6 mm i n s i z e has been observed, r e s u l t i n g i n decreased degradation of the s u b s t r a t e . For reasonable comparisons a c o n s i s t e n t method should be maintained. As the sample s i z e f o r a given bag s i z e was i n c r e a s e d reduced d e g r a d a b i l i t y was observed (Orskov et a l . , 1980). A p p a r e n t l y , the s m a l l e s t amount of sample necessary should y i e l d adequate m a t e r i a l f o r a n a l y s i s a f t e r i n c u b a t i o n . The p o s i t i o n of the bags in the rumen has been the s u b j e c t of c o n f l i c t i n g r e s u l t s . Increased d i g e s t i o n was r e p o r t e d i n the rumen v e n t r a l sac (Balch and Johnson, 1950). Based on l a t e r work, Orskov et a l . (1980) concluded that the p o s i t i o n of bags in the rumen had l i t t l e or no e f f e c t on feed d e g r a d a t i o n . F u r t h e r , these workers d i d not n o t i c e any r e d u c t i o n i n the v a r i a b i l i t y i n DM disappearance between bags - when a t t a c h e d to weights so as to anchor i n the ventrar~~sac of the rumen. V a r i a t i o n between bags was reduced when the the bags were anchored with about 25cm of nylon c o r d to the . .20 cannula top i n sheep and with about 50cm or more i n c a t t l e (Orskov, 1982; Orskov et a l . , 1980; De Boer et a l . , 1986; Weakley et a l . , 1983). Some workers have employed p o l y e s t e r mesh bags to c o n t a i n s m a l l nylon bags (De Boer et a l . , 1986). Others have used s i n k e r s (250ml p l a s t i c b o t t l e s f i l l e d with pebbles and water) to p o s i t i o n the bags i n the v e n t r a l sac of the rumen (Orskov et a l . , 1980). The measurement of the r a t e of d e g r a d a t i o n r e q u i r e s t h a t the i n c u b a t i o n p e r i o d be spread over a s p e c i f i e d p e r i o d . The t o t a l time f o r complete d e g r a d a t i o n v a r i e s with the m a t e r i a l being incubated, and hence the i n t e r m e d i a t e times chosen w i l l a l s o v a r y . For an adequate and r e l i a b l e mathematical d e s c r i p t i o n , Orskov (1982) recommends t h a t the asymptote and other s e n s i t i v e p a r t s of the curve be w e l l supported by o b s e r v a t i o n s . The d i e t given to the animals f i t t e d with nylon bags should be s i m i l a r to the d i e t s f o r which the r e s u l t s are to be a p p l i e d . R e s u l t s o b t a i n e d by Orskov (1982) i n d i c a t e d that p r o t e i n supplements of v e g e t a b l e o r i g i n were degraded more slowly i n animals given a h i g h - c o n c e n t r a t e as compared with a high-roughage d i e t . Working with sheep on b a r l e y , Orskov et a l . (1980), found that animals c o n t r i b u t e d the h i g h e s t v a r i a t i o n i n dry matter and n i t r o g e n disappearance from i n s i t u bags. However, Weakley et a l . , (1983) observed 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) in i n s i t u dry matter disappearance among the four . .21 cows they fed with soybean meal. D i f f e r e n c e s among cows i n de g r a d a t i o n of n i t r o g e n from soybean meal approached s i g n i f i c a n c e ( P < 0 . 1 0 ) at 1 2 hours of i n s i t u exposure. They t h e r e f o r e concluded t h a t i t may be needless to be concerned wi t h animal e f f e c t s on i n s i t u measurements from s u b s t r a t e s p h y s i c a l l y s i m i l a r to soybean meal. . . 2 2 MATERIALS AND METHODS Two mature Ayrshire steers f i t t e d with a permanent rumen cannula were used. The animals were fed twice d a i l y with a l f a l f a cubes and orchard grass hay at 50:50 r a t i o (dry basis). The feed was offered ad libitum in two sequences, in the morning and afternoon. Forage samples were c o l l e c t e d in the Kenya Highlands after the long rains (Table 1). Sample c o l l e c t i o n and preparation methods used are outlined by Harris (1971). At least ten sampling locations were established in the f i e l d and 2.5kg of fresh material obtained. A l l samples were dried at 60 to 70°C for 48 to 72 hours and ground through a 2mm screen. The method used i s as outlined by Orskov et a l . (1980).Dacron bags, ( 5 * 1 1 cm) made from nylon and having 40nm diameter pore s i z e , were used throughout the study. Sample sizes and incubation i n t e r v a l varied with the type of material under study as outlined by Orskov et a l . (1980). Dacron bags with test material were incubated in the rumen. The interval between incubations was 6 hours, s t a r t i n g with 1 hour (Satter, 1986). This was followed by 6, 12, l8,...upto 72 hours^incubation periods. A l l samples were incubated at least in duplicate. Results that varied markedly (CV >15%) were repeated. A 10 cm long s t r i n g t i e d individual . .23 bags on to a 50 cm main s t r i n g . The bags were positioned in the ventral sac of the rumen with the help of a sinker ( p l a s t i c bottle f u l l of sand and water). The sinker was t i e d to the t i p of the main s t r i n g . Immediately after r e t r i e v a l from the rumen, the bags were soaked in a reservoir f u l l of cold water for 5 minutes. Careful hand washing was done for 10 to 15 minutes to remove rumen f l u i d and any debris s t i c k i n g on the bags. The bag material was cleaned by rubbing between the finger and thumb and, then rinsing in the cold water. Cleanliness of the bags was then ascertained by using the running tap procedure (Orskov et a l . 1980). The bags were then dried in an oven at 60-70°C for 48-72 hours. DM and CP contents were then determined. A l l samples were analysed for DM, CP (Parkinson and A l l e n , 1975) NDF and ADF (Waldern, 1971) and t o t a l ash (Chapman and Pratt, 1961) before incubation. After r i n s i n g and drying, the samples were again analysed for DM and CP. The General Linear Model of the SAS S t a t i s t i c a l Package (1985) was used for a l l s t a t i s t i c a l comparisons. The experimental model employed was a 12(incubation time)*32 (forage samples) f a c t o r i a l in a completely randomized design. The treatment effect was composed of the forage sample effect and the incubation time e f f e c t . An interaction e f f e c t between incubation time and the forage samples was also tested for. .24 Table 1:Names and stage of harvesting of the forage samples. SAMPLE NAME: GROWTH STAGE. SCIENTIFIC NAME. FODDER GRASSES. Giant Panicum Early vegt. Edible Canna Early vegt. Guatemala grass Early vegt. Pakistani hybrid Early vegt. French Cameroon Early vegt. Clone.13 Early vegt. Clone.13 Regr. flower Bana grass Early vegt. Bana grass Regr. vegt. Bana grass Regr. flower Green Maize chop Milk stage Fodder Sorghum Late vegt. Fodder Sorghum F u l l bloom PASTURE GRASSES. Kikuyu grass Regr. flower P. trachyphyllum Regr. flower Stargrass Stargrass Red Oat grass Red Oat grass Rhodes grass Rhodes grass LEGUMES. Lucerne Lucerne Lucerne Lucerne Desmodium spp. CROP RESIDUES, Rhubarb leaves Banana leaves Maize stover Wheat bran Wheat straw Sweet Potato vines Regr.flower(RF Late vegt. F u l l bloom Mid bloom Late bloom Mid bloom Late bloom Early vegt. Mid bloom Mid bloom Late bloom Early seed Early vegt. Regr. flower Post ripe Post ripe (EV (EV (EV (EV (EV (EV (RF (EV (RV (RF (MS (LV (FB (RF (RF (LV (FB (MB (LB (MB (LB (EV (MB (MB (LB (ES (EV (RF (PR (PR Panicum antidotale Canna edulis Tripsacum fasciculatum Pennisetum purpureum P. purpureum P. purpureum P. purpureum P. purpureum P. purpureum P. purpureum Zea mays Sorghum sudanense S. sudanense Pennisetum clandestinum  Pennisetum trachyphyllum  Cynodon plectostachyus C. plectostachyus  Themeda triandra T. tr iandra Chloris qayana C. gayana Medicago sativa M. sativa M. sativa M. sativa Desmodium uncinartum Rheum rhabarbarum  Musa species  Zea mays Triticum eastivum T. aestivum  Ipomoea batatas [Vegt.-Vegetative Regr.-Regrowth Flower -Flowering] . 2 5 RESULTS Chemical composition. Clone. 13 and bana grass v a r i e t i e s dropped markedly in q u a l i t y between the vegetative and the flowering stage (Table 2). This was marked by a f a l l in the CP content and an increase in both ADF and NDF contents. Green maize chop and sorghum were of higher q u a l i t y than the other fodder grasses. The negative effects of maturity on the chemical composition of maize and sorghum was characterised by a drop of over fiv e percentage points in the CP contents, between the two stages sampled. The c e l l wall contents increased over the same per iods. Pasture grasses were generally of lower q u a l i t y than the fodder ones. Declines in quality were also observed with matur i ty. Lucerne and desmodium tended to remain high in CP content over the sampled period. A high proportion of c e l l wall contents was observed in desmodium. A great variation in chemical composition existed within the various crop by-products sampled. Rhubarb leaves, sweet potato vines, banana leaves and wheat bran were high in CP content. Maize stover and wheat straw were high in c e l l wall contents. It may be desirable to compare s t a t i s t i c a l l y , the various degradation rate constants (a,b and c ) . However, the . .26 Table 2:Chemical composition of forage samples. SAMPLE NAME. AGE %DM %CP %ADF %NDF %ASH FODDER GRASSES. Giant panicum EV 92 .45 8. 47 49. 75 73. 47 16. 53 Edib le canna EV 93 .25 14. 91 48. 75 70. 67 12. 63 Guatemala grass EV 91 .91 12. 1 0 50. 02 74. 37 13. 98 Pakis tani hybrid EV 94 .38 9. 45 47. 74 71 . 43 22. 94 French Cameroon EV 94 .45 7. 36 51 . 32 78. 40 24. 08 Clone.13 EV 93 .84 16. 64 40. 09 64. 89 19. 09 Clone.13 RF 94 .04 4. 1 1 58. 99 84. 69 9. 08 Bana grass EV 94 .49 9. 18 44. 41 68. 05 20. 57 Bana grass RV 93 .75 10. 83 54. 94 75. 05 13. 30 Bana grass RF 93 .51 6. 92 49. 90 74. 21 13. 84 Green maize chop MS 92 .07 14. 16 40. 15 69. 31 12. 54 Fodder sorghum LV 92 .87 17. 34 36. 47 65. 35 13. 24 Fodder sorghum FB 93 .83 1 1 . 68 44. 38 75. 25 10. 83 PASTURE GRASSES. Kikuyu grass RF 94 .43 13. 80 35. 58 78. 99 15. 76 P. trachyphyllum RF 94 .85 1 1 . 74 44. 08 77. 27 16. 78 Naivasha stargrass LV 94 .42 7. 1 4 53. 31 80. 80 12. 84 Naivasha stargrass FB 94 . 1 2 6. 1 4 49. 86 85. 89 7. 99 Red oat grass MB 94 .90 5. 70 48. 69 80. 51 9. 32 Red oat grass LB 94 .74 5. 21 54. 40 82. 68 9. 82 Rhodes grass MB 93 .93 5. 93 46. 90 79. 46 10. 45 Rhodes grass LB 94 .36 8. 29 48. 04 85. 99 10. 85 LEGUMES. Lucerne EV 93 .33 20. 22 38. 86 55. 34 15. 30 Lucerne MB 93 .18 18. 78 38. 1 4 58. 08 12. 46 Lucerne . MB 93 .64 19. 19 41 . 30 55. 48 10. 97 Lucerne LB 92 .71 21 . 97 43. 38 56. 53 14. 18 Desmodium ES 93 .38 15. 84 60. 44 70. 1 6 8. 85 CROP RESIDUES. Rhubarb leaves EV 91 .72 14. 02 18. 59 23. 22 13. 02 Banana leaves RF 94 .46 15. 42 39. 44 75. 74 13. 1 7 Maize stover PR 94 .95 5. 39 49. 25 81 . 50 8. 27 Wheat bran 92 .72 16. 09 19. 26 58. 60 5. 97 Wheat straw PR 94 .03 5. 72 50. 21 73. 22 10. 99 Sweet potato vines RF 92 .33 20. 53 39. 73 42. 63 17. 93 .27 r e l a t i v e l y s m a l l number of data p o i n t s measured i n t h i s study makes the a n a l y s i s of a d d i t i o n a l parameters d i f f i c u l t . In the r e s u l t s d i s c u s s e d below i n c u b a t i o n time and sample e f f e c t s i g n i f i c a n t l y (P<0.05) i n f l u e n c e d the extent of sample de g r a d a t i o n i n the rumen. The i n t e r a c t i o n e f f e c t between forage samples and the time of i n c u b a t i o n was not s i g n i f i c a n t (P<0.05). Fodder grasses. F i g u r e 1 shows a t y p i c a l d e g r a d a t i o n curve o b t a i n e d f o r fodder g r a s s e s . The R-squared val u e s f o r the model used to e x p l a i n DM and CP d e g r a d a b i l i t y were 86 and 93% r e s p e c t i v e l y . During the f i r s t 36 hours the major d i f f e r e n c e s i n disappearance were s i g n i f i c a n t l y (P<0.05) e s t a b l i s h e d . Table 3 and 4 show the DM and CP d e g r a d a t i o n c o n s t a n t s . Clone.13, P a k i s t a n i h y b r i d and e d i b l e canna v a r i e t i e s had moderate DM and CP s o l u b i l i t i e s (15-20%) at the e a r l y stage of growth. These re p r e s e n t e d a p r o p o r t i o n a l s o l u b i l i t y between the p r o t e i n and the non-nitrogenous feed components. The r a p i d l y s o l u b l e p r o t e i n f r a c t i o n 'a' and the p o t e n t i a l l y degradable p r o t e i n 'b' f r a c t i o n of g i a n t panicum and Guatemala grass were r e l a t i v e l y s i m i l a r . From Table 5 and 6, e f f e c t i v e CP and DM d e g r a d a t i o n f o r g i a n t panicum was s i g n i f i c a n t l y (P<0.05) h i g h e r than f o r Guatemala g r a s s . The higher r a t e s of DM and CP d e g r a d a t i o n 'c' f o r g i a n t panicum c o n t r i b u t e d p o s i t i v e l y to t h i s e f f e c t . P a k i s t a n i h y b r i d had a . .28 F i g 1: % Degradation Versus incubation Time, c Q 0 o •s o D Green Maize Chop. 100 Time Incubated in the Rumen [Hrs]. % DM Degraded. * * C P graded. 29 Table 3: Dry Matter Degradation Constants. SAMPLE NAME. AGE a b FODDER GRASSES. Giant panicum EV 14. ,44 45. .56 4. ,9 Edible canna EV 22. .22 43. .33 3. ,2 Guatemala grass EV 13. .33 54. ,44 2. ,8 Pakistani hybrid EV 15. ,55 46. .67 5. ,4 French Cameroon EV 16. ,66 48. ,89 4. ,0 Clone.13 EV 17. .77 55. .56 4. , 1 Clone.13 RF 10. ,00 46. ,66 3. .6 Bana grass EV 16. ,66 51 .  1 1 6. , 1 Bana grass RV 18. .88 55. .56 4. .9 Bana grass RF 1 1 . . 1 1 50, .00 4. .9 Green maize chop MS 32, .22 48. .89 4. .3 Fodder sorghum LV 24. .44 54, .44 5. ; 1 Fodder sorghum FB 15. .55 48. .89 4. .6 PASTURE GRASSES. Kikuyu grass RF 21 . 1 1 55, .55 4. ,7 P. trachyphyllum RF 21 , . 1 1 54. .44 6. .2 Naivasha stargrass LV 12. .22 47, .77 4. ,0 Naivasha stargrass FB 10. .00 31 , . 1 1 3. .5 Red oat grass MB 10. .00 47, .77 3. .8 Red oat grass LB 8, .88 44, .45 3. .8 Rhodes grass MB 10. .00 47, .77 3. .8 Rhodes grass LB 16. .66 43, .90 4. .7 LEGUMES. Lucerne EV 25. .55 43, .33 6. .8 Lucerne MB 23. .33 44, .44 5, .5 Lucerne MB 24, .44 36, .67 10, .9 Lucerne LB 24. . 44 37, .78 4, .0 Desmodium ES 13, .33 36, .66 3, .4 CROP RESIDUES. Rhubarb leaves EV 20. .00 69, .99 6, .7 Banana leaves RF 21 , . 1 1 28, .89 3, .8 Maize stover PR 1 1 , . 1 1 48, .88 3, .4 Wheat bran 25, .55 47, .78 8, .9 Wheat straw PR 12, .22 45, .55 3, .3 Sweet potato vines RF 27, .77 50, .00 7, .9 a= % s o l u b i l i t y , b= p o t e n t i a l l y degradable f r a c t i o n [%], c= rate of degradation of the 'b' fr a c t i o n [%/hr]. .30 Table 4: Crude Protein Degradation Constants. SAMPLE NAME. AGE a b FODDER GRASSES. Giant panicum EV 12. .22 54, .45 7. .0 Edible Canna EV 18, .89 44. .44 1 . .6Guatemala grass EV 12, .22 58, .89 2. .2 Pakistani hybrid EV 21 , . 1 1 46, .67 0. .4 French Cameroon EV 7, .00 63, .00 4. .0 Clone.13 EV 18, .89 61 , . 1 1 6. .0 Clone.13 RF 1 Bana grass EV l\ .22 70! .56 6! .6 Bana grass RV 9, .44 53, .89 0, .9 Bana grass RF 13, .89 65, .00 3, .2 Green maize chop MS 22, .22 55, .56 8, .6 Fodder sorghum LV » Fodder sorghum FB 1 1 , .67 58! .33 6! .6 PASTURE GRASSES. Kikuyu grass RF 20, .00 60, .00 7, . 1 P. trachyphyllum RF 20, .00 60, .00 4, .7 Naivasha stargrass LV 10, .00 65, .56 1 , . 1 Naivasha stargrass FB 7, .78 46, .66 3, .3 Red oat grass MB K > Red oat grass LB 10, .00 57! !78 2, !s Rhodes grass MB 8, .00 50, .00 6, .4 Rhodes grass LB 14, .44 51 . 1 2 2, . 1 LEGUMES. Lucerne EV 18. .33 60. .00 9, . 1 Lucerne MB 20, .00 65. .56 6, .2 Lucerne MB 20. .00 60, .00 6, .5 Lucerne LB 20, .00 53. .89 7, .7 Desmodium ES 1 1 , . 1 1 51 . 67 4, .0 CROP RESIDUES. Rhubarb leaves EV 65, .56 21 . 1 1 6. .6 Banana leaves RF 22. .78 35. .00 3, .9 Maize stover PR 7. .22 50. .56 6, .2 Wheat bran 8. .33 53. .34 6, .2 Wheat straw PR 7. ,83 72. .78 7. .6 Sweet potato vines RF 21 . 1 1 62. .22 4. .8 a= % s o l u b i l i t y , b= p o t e n t i a l l y degradable f r a c t i o n [%], c= rate of degradation of the 'b' fraction [%/hr]. .31 Table 5: E f f e c t i v e Dry Matter Degradation. SAMPLE NAME. AGE k = 0. 03 0. 04 0. 05 0. 06 0 .07 FODDER GRASSES. Giant panicum EV 42. 70 39. 52 36. 99 34. 92 33 .20 E d i b l e canna EV 44. 56 41 . 48 39. 1 3 37. 29 35 .81 Guatemala grass EV 39. 61 35. 75 32. 87 30. 65 28 .88 P a k i s t a n i h y b r i d EV 45. 55 42. 36 39. 78 37. 66 35 .87 French Cameroon EV 44. 60 44. 1 1 38. 39 36. 22 34 .55 Clone.13 EV 49. 85 45. 89 42. 80 40. 32 38 .29 Clone.13 RF 35. 45 32. 10 29. 53 27. 50 25 .85 Bana grass EV 50. 92 47. 53 44. 75 42. 43 40 .46 Bana grass RV 53. 34 49. 47 46. 38 43. 86 41 .76 Bana grass RF 42. 1 2 38. 64 35. 86 33. 59 31 .70 Green maize chop MS 61 . 02 57. 55 54. 83 52. 63 50 .82 Fodder sorghum LV 58. 72 54. 95 51 . 93 49. 45 47 .39 Fodder sorghum FB 45. 1 4 41 . 70 38. 98 36. 77 34 .94 PASTURE GRASSES. Kikuyu grass RF 55. 02 51 . 1 2 48. 03 45. 51 43 .42 P. tr a c h y p h y l l u m RF 57. 80 54. 20 51 . 25 48. 78 46 .68 Naivasha s t a r g r a s s LV 39. 43 36. 42 33. 38 31 . 24 29 .51 Naivasha s t a r g r a s s FB 57. 30 53. 28 49. 89 46. 99 44 .49 Red oat grass MB 36. 70 33. 27 30. 63 28. 52 26 .81 Red oat grass LB 33. 72 30. 54 28. 07 26. 1 2 24 .52 Rhodes grass MB 32. 68 30. 41 28. 57 27. 05 25 .78 Rhodes grass LB 43. 46 40. 38 37. 93 35. 94 34 .30 LEGUMES. Lucerne EV 55. 62 52. 83 50. 52 48. 57 46 .90 Lucerne MB 53 . 20 51 . 27 49. 58 48. 09 46 .77 Lucerne MB 52. 09 49. 06 46. 61 44. 58 42 .88 Lucerne LB 46. 03 43. 33 41 . 23 39. 55 38 . 18 Desmodium ES 32. 81 30. 1 7 28. 1 7 26. 59 25 .32 CROP RESIDUES. Rhubarb leaves EV 68. 34 63. 83 60. 08 56. 92 54 .23 Banana le a v e s RF 37. 25 35. 18 33. 59 32. 31 31 .28 Maize s t o v e r PR 37. 08 33. 57 30. 89 28. 79 27 .09 Wheat bran 61 . 28 58. 51 56. 1 4 54. 09 52 .29 Wheat straw PR 36. 08 32. 81 30. 33 28. 38 26 .81 Sweet potato v i n e s RF 64. 01 60. 96 58. 39 56. 19 54 .28 k= rumen d i g e s t a flow r a t e [ % / h r ] . .32 Table 6: E f f e c t i v e Crude Prote in D e g r a d a b i l i t y . 5AMPLE NAME. AGE k= 0.03 0. 04 0 .05 0 .06 0 .07 FODDER GRASSES. Giant panicum EV 50. 34a 46. 88 43. 99 41 .55 39. 45 Edib le canna EV 34. 76hs 31 . 96 30. 00 28 .55 27. 44 Guatemala grass EV 37. 45h 33. 41 30. 49 28 .28 26. 54 Pakis tani hybrid EV 27. 67f 26. 20 25. 28 24 .63 24. 1 6 French Cameroon EV 43. 20e 38. 71 35. 20 32 .40 30. 10 Clone.13 EV 59. 69t 55. 62 52. 28 49 .51 47. 1 6 Clone.13 RF # • • Bana grass EV 55. 79q 51 . 23 47. 44 44 !26 41 . 54 Bana grass RV 21 . 98nf 19. 43 17. 73 16 .53 15. 64 Bana grass RF 47. 52g 42. 86 39. 34 36 .58 34. 35 Green maize chop MS 63. 40x 60. 1 3 57. 34 54 .94 52. 84 Fodder sorghum LV • Fodder sorghum FB 51 . 94qa 48. 1 7 45. 05 42 .42 40 ! 18 PASTURE GRASSES. Kikuyu grass RF 62. 31 tx 58. 53 55. 36 52 .68 50. 37 P. trachyphyllum RF 56. 83t 52. 63 49. 29 46 .57 44. 31 Naivasha stargrass LV 28. 60fs 25. 01 22. 59 20 .83 19. 51 Naivasha stargrass FB 32. 32hs 28. 97 26. 43 24 .43 22. 81 Red oat grass MB • # Red oat grass LB 38. 1 1h 34. 00 30. 94 28 .57 26! 68 Rhodes grass MB 42. 1 6he 38. 90 36. 20 33 .94 32. 02 Rhodes grass LB 35. 64hs 32. 18 29. 69 27 .81 26. 35 LEGUMES. Lucerne EV 63. 54xm 60. 1 1 57. 1 6 54 .60 52. 36 Lucerne MB 64. 22m 59. 89 56. 34 53 .36 50. 84 Lucerne MB 61 . 24xm 57. 35 54. 1 3 51 .42 49. 1 1 Lucerne LB 58. 88t 55. 58 52. 79 50 .41 48. 36 Desmodium ES 59. 60tx 55. 26 51 . 80 48 .98 46. 63 CROP RESIDUES. Banana leaves RF 40. 84b 37. 1 5 34. 28 31 .97 30. 09 Rhubarb leaves EV 80. 1 Op 78. 73 77. 60 76 .65 75. 84 Maize stover PR 42. 65e 40. 1 5 38. 20 36 .65 35. 38 Wheat bran 41 . 29h 37. 95 35. 21 32 .92 30. 97 Wheat straw PR 44. 43eg 40. 92 38. 03 35 .61 33. 55 Sweet potato vines RF 82. 22p 79. 1 3 76. 33 73 .78 71 . 47 k= rumen digesta flow rate [%/hr]. Values with d i f f eren t l e t t e r s are s i g n i f i c a n t l y d i f f e r e n t at (P<0.05). .33 r e l a t i v e l y low r a t e of CP d e g r a d a t i o n and a s m a l l e r 'b' f r a c t i o n . The net r e s u l t f o r CP degradation was t h e r e f o r e a s i g n i f i c a n t l y (P<0.05) lower e f f e c t i v e CP d e g r a d a b i l i t y . Bana grass v a r i e t i e s had moderate DM s o l u b i l i t y 'a' and r a t e of degradation 'c'. These tended to d e c l i n e with m a t u r i t y , and t h e r e f o r e had a s i g n i f i c a n t (P<0.05) e f f e c t on e f f e c t i v e DM d e g r a d a b i l i t y . CP s o l u b i l i t i e s of bana grass v a r i e t i e s were low a l t h o u g h the r a t e of CP d e g r a d a t i o n 'c' was s l i g h t l y higher than f o r the other n a p i e r v a r i e t i e s . The r a t e of CP d e g r a d a b i l i t y decreased with m a t u r i t y , r e s u l t i n g in a s i g n i f i c a n t (P<0.05) r e d u c t i o n i n e f f e c t i v e CP d e g r a d a t i o n . Green maize chop and fodder sorghum had r e l a t i v e l y h i g h DM and CP s o l u b i l i t i e s and a l s o degraded r a p i d l y (high 'c' v a l u e s ) . These c o n t r i b u t e d p o s i t i v e l y to the 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 e f f e c t i v e d e g r a d a t i o n between these two f e e d s t u f f s and the n a p i e r v a r i e t i e s . S o l u b i l i t i e s (DM and CP) d e c l i n e d with m a t u r i t y f o r both maize and sorghum. An i n c r e a s e i n the p r o p o r t i o n of p o l y s a c c h a r i d e s and i n s o l u b l e p r o t e i n s with m a t u r i t y c o u l d p o s s i b l y be the cause. Pasture g r a s s e s . F i g u r e 2 shows the t y p i c a l pasture g r a s s d e g r a d a t i o n curves o b t a i n e d . The model f i t t e d e x p l a i n e d 94 and 88% of the v a r i a t i o n r e s u l t i n g from DM and CP d e g r a d a t i o n i n the rumen. Except f o r Pennisetum s p e c i e s and l a t e bloom rhodes . .34 g r a s s , the other grasses had low s o l u b i l i t y (<14%). Degradation r a t e s 'c' e i t h e r decreased or remained r e l a t i v e l y c o nstant with m a t u r i t y . However, the Pennisetum s p e c i e s had r e l a t i v e l y high degradation r a t e 'c' c o n s t a n t s and s i g n i f i c a n t l y higher (P<0.05) e f f e c t i v e d e g r a d a t i o n than the other pasture g r a s s e s . For a l l pasture grasses there was an a p p r e c i a b l e p o t e n t i a l f o r degradation ('b' f r a c t i o n ) . W i t h i n the f i r s t 30 hours the major d i f f e r e n c e s i n disappearance had been s i g n i f i c a n t l y (P<0.05) e s t a b l i s h e d . Legumes. F i g u r e 3 shows t y p i c a l legume d e g r a d a t i o n curves o b t a i n e d . The equations f i t t e d e x p l a i n e d 91.6 and 88.4% of the v a r i a t i o n i n DM and CP degraded i n the rumen re s p e c t i v e l y . DM and CP s o l u b i l i t y 'a' were q u i t e high (>18%) except f o r desmodium which was l e s s than 14%. A l s o the d e g r a d a t i o n r a t e c o n s t a n t s were hi g h a v e r a g i n g 0.06 and 0.08 f o r DM and CP r e s p e c t i v e l y . The p r o p o r t i o n of p o t e n t i a l l y degradable 'b' f r a c t i o n was lower f o r DM than f o r the CP. P o s s i b l y , t h i s shows t h a t CP formed the g r e a t e r p r o p o r t i o n of the i n s o l u b l e m a t e r i a l a f t e r one hour of i n c u b a t i o n . Within 36 Hours p o s t -i n c u b a t i o n the major d i f f e r e n c e s i n degr a d a t i o n had been " e s t a b l i s h e d s i g n i f i c a n t l y (P<0.05). A s i g n i f i c a n t (P<0.05) d e c l i n e o c c u r r e d between the e f f e c t i v e DM and CP degraded as lu c e r n e matured. Lucerne had . .35 36. Fig 3: % Degradation Versus Incubation Time. Lucerne (LB). 100 - i — — 90 -80 -\ 10 ~\ o H 1 1 1 1 1 1 1 l 0 20 40 60 80 Time Incubated in the Rumen [Hrs]. D % DM Degraded. +• % CP Degraded. 37 F i g 4:% Degradation Versus Incubation Time. Rhubarb Leaves. 100 -i • 10 H o H 1 1 1 1— 1 1 1 1 0 20 40 60 80 Time Incubated in the Rumen [Hrs]. • % DM Degraded. +• % CP Degraded. 3G high (>60%) e f f e c t i v e CP degradation. Desmodium was both r e l a t i v e l y insoluble and undegradable. Crop residues. Figure 4 shows t y p i c a l crop residues degradation curves obtained. The models f i t t e d explained 90.7 and 89.8% of the variation in the DM and CP degraded in the rumen respectively. At the end of 36-42 hours of incubation, the major disappearances had already been s i g n i f i c a n t l y (P<0.05) established. Crude protein and dry matter in rhubarb leaves, banana leaves, wheat straw and sweet potato vines were highly soluble. Except for wheat straw, the others have high CP content. Rhubarb leaves and wheat straw protein i s both highly soluble and degradable. However, the CP content of wheat straw was quite low (5.7%) and the predominant proportion of the DM was neither soluble nor degradable. Hence, the e f f e c t i v e DM degradability of Wheat straw was s i g n i f i c a n t l y (P<0.05) lower than for rhubarb leaves. Although rhubarb leaves were highly soluble, the degradation rate 'c' for both i t s DM and CP remained quite high. This resulted in high e f f e c t i v e degradabi1 i t i e s for the rhubarb leaves. Difference in disappearance due to the small p a r t i c l e size are s i g n i f i c a n t l y established during the f i r s t hour of i n - s i t u exposure (Weakley et a l . , 1983). This was also observed with the rhubarb leaves. Banana leaves were marked by low DM and CP degradation rates 'c' and a small . .39 p o t e n t i a l l y degradable f r a c t i o n *b'. E f f e c t i v e DM and CP deg r a d a t i o n f o r banana le a v e s was t h e r e f o r e mainly the r e s u l t of the s o l u b l e f r a c t i o n 'a', and hence remained q u i t e low. The CP s o l u b i l i t y of wheat bran and maize s t o v e r were q u i t e s i m i l a r . However the DM s o l u b i l i t y of wheat bran was about two times higher than f o r maize stover or wheat straw. T h i s shows that the p o l y s a c c h a r i d e components of Wheat bran were more s o l u b l e than s i m i l a r components i n wheat straw and maize s t o v e r . The DM d e g r a d a t i o n constant 'c' f o r wheat bran was approximately three times t h a t of e i t h e r wheat straw or maize s t o v e r . The r e s u l t s then were a s i g n i f i c a n t l y higher (P<0.05) e f f e c t i v e DM d e g r a d a b i l i t y f o r wheat bran. Though wheat bran had a high CP content r e l a t i v e to maize s t o v e r , the CP s o l u b i l i t y , CP d e g r a d a t i o n r a t e 'c' and p o t e n t i a l l y degradable f r a c t i o n s 'b' were low. T h i s t h e r e f o r e r e s u l t e d i n s i g n i f i c a n t l y lower (P<0.05) e f f e c t i v e CP d e g r a d a b i l i t y f o r maize s t o v e r . From t h i s t r i a l wheat bran i s shown to be a good source of degradable c a r b o h y d r a t e s . .40 DISCUSSION The t o t a l d e g r a d a b i l i t y of a feed i n the rumen i s given by (a+b). T h i s r e p r e s e n t s the amount of p r o t e i n which can be d i s s o l v e d and degraded w i t h i n the rumen g i v e n s u f f i c i e n t time. The sum (a+b) cannot t h e r e f o r e exceed 100%. The undegradable f r a c t i o n i n the rumen would be r e p r e s e n t e d by l00-(a+b). E f f e c t i v e d e g r a d a b i l i t y i s giv e n by 'P', and re p r e s e n t s the amount of a feed which i s a c t u a l l y degraded in the rumen at a s p e c i f i c passage r a t e . Hence the lower the turnover r a t e of the rumen d i g e s t a , the g r e a t e r w i l l be the value of 'P'. E d i b l e canna, P a k i s t a n i h y b r i d and banana leaves had high s o l u b i l i t i e s but low e f f e c t i v e d e g r a d a b i l i t i e s . T h e i r low d e g r a d a t i o n r a t e s 'c' c o u l d have p l a y e d a major r o l e i n the s i g n i f i c a n t l y (P<0.05) low e f f e c t i v e d e g r a d a b i l i t i e s (<40%) r e a l i z e d . As was a l s o observed by Mahadevan et a l . (1980) and S e t a l a (1983), t h i s shows that p r o t e i n s o l u b i l i t y may not be a good measure of the p r o t e i n d e g r a d a b i l i t y . For f e e d s t u f f s • w i t h r e l a t i v e l y h i g h d e g r a d a t i o n r a t e s 'c', e.g green maize chop, fodder sorghum, kikuyu g r a s s , l u c e r n e and sweet po t a t o v i n e s , s o l u b i l i t y c o u l d be r e l a t e d to rumen d e g r a d a b i l i t y more a c c u r a t e l y . Hence, the p r o p o r t i o n of i n s o l u b l e p r o t e i n and i t s rumen d e g r a d a t i o n r a t e s i g n i f i c a n t l y i n f l u e n c e the e f f e c t i v e and/or extent of . .41 degradation. The decline in s o l u b i l i t y and e f f e c t i v e degradability with maturity of legumes, fodder and pasture grasses could be att r i b u t e d to the gradual dominance of stem tissue over leaf tissue and an increase in l i g n i f i e d s t r u c t u r a l polysaccharides (Llano and De Peters, 1985). With maturity, there were increases in both ADF and NDF content of the feedstuffs sampled (Table 2). A negative r e l a t i o n s h i p between the degree of l i g n i f i c a t i o n and c e l l w a l l digestion in forages is well recognized (Van Soest, 1982). The decline in the grass CP s o l u b i l i t y concurs with the observations made by Clark (1975). The s l i g h t increase in CP s o l u b i l i t y of lucerne with age while e f f e c t i v e CP degradation s i g n i f i c a n t l y decreased, again point out the inadequacy of s o l u b i l i t y as a r e l i a b l e indicator of rumen degradation even within similar feeds. Clark (1975) also noted that the soluble nitrogen content of forages i s greatest at maturity except for cereal grains. Wheat bran had a low CP s o l u b i l i t y and e f f e c t i v e degradation though i t s CP content was high (16%). Its s i g n i f i c a n t l y (P<0.05) higher DM s o l u b i l i t y and e f f e c t i v e degradability show that wheat bran is a good source of rumen degradable energy and add i t i o n a l i n t e s t i n a l protein supply. Wheat bran "contains insoluble proteins e.g g l i a d i n , g l u t e l i n and other residue proteins (Inglett, 1974). The s o l u b i l i t y and e f f e c t i v e degradability of wheat bran was observed to be . .42 q u i t e low {Table 4 and 6). T h i s agrees with Wohlt et a l . (1973) who a l s o r e p o r t e d low s o l u b i l i t y with prolamins and g l u t e l i n s as major p r o t e i n f r a c t i o n s i n feeds. C e r e a l g r a i n s and p r o t e i n supplements c o n t a i n four main types of p r o t e i n s i n c l u d i n g albumin, g l o b u l i n s , prolamins, and g l u t e l i n s . Albumins and g l o b u l i n s are low molecular weight p r o t e i n s that are s o l u b l e i n ruminal f l u i d (Wohlt et a l . , 1973). G l u t e l i n s and prolamins are higher molecular weight p r o t e i n s that c o n t a i n d i s u l f i d e bonds, which make them l e s s s o l u b l e i n the ruminal f l u i d ( C l a r k et a l . , 1987). P r o t e i n s that have a low s o l u b i l i t y i n the ruminal f l u i d , and that c o n t a i n e x t e n s i v e c r o s s - l i n k i n g , such as would be pr o v i d e d by the d i s u l f i d e bonds of g l u t e l i n s , are l e s s a c c e s s i b l e to the p r o t e o l y t i c enzymes and are a l s o r e l a t i v e l y r e s i s t a n t to d e g r a d a t i o n . To determine the u t i l i z a t i o n of wheat bran abomasal d i g e s t i o n and i n t e s t i n a l amino a c i d s a b s o r p t i o n from Wheat bran p r o t e i n would have to be i n v e s t i g a t e d . In c o n t r a s t to wheat bran, maize s t o v e r and wheat straw were low i n CP. The a p p r e c i a b l e CP s o l u b i l i t y and e f f e c t i v e d e g r a d a b i l i t y f o r wheat straw may e r r o n e o u s l y endorse t h i s f e e d s t u f f as a good source of rumen degradable p r o t e i n . Such a move however ought to c o n s i d e r the CP content and other r e l a t e d f a c t o r s of wheat straw. V o l u n t a r y feed intake would be depressed due to the low CP ( l e s s than 8%) content (Van Soest, 1982). T h i s l e v e l i s below the n i t r o g e n requirement of rumen b a c t e r i a , even though supplemented by r e c y c l i n g of . .43 urea. The result i s a depression in d i g e s t i b i l i t y associated with nitrogen deficiency in the rumen. Therefore, both maize stover and wheat straw would be inadequate i f supplied as complete feeds. In view of i t s high CP s o l u b i l i t y and degradability, the soluble protein in banana leaves i s l i k e l y to be comprised of albumins and globulins. These proteins are more degradable in the rumen than are prolamins and g l u t e l i n s (Wohlt et a l . , 1973). The p o s s i b i l i t y of banana leaves protein being f u l l y u t i l i s e d by rumen microbes i s quite high. With th e i r high s o l u b i l i t y and e f f e c t i v e degradability rhubarb leaves and sweet potato vines are promising feedstuffs in dairy production. Rhubarb leaves are high in oxalates, but the predominant carbohydrate fermenters of the rumen are unable to degrade oxalates. Feeding of rhubarb leaves would be expected to increase the proportions of the anaerobic oxalate-degrading bacteria (Hobson and Wallace, 1982), thus enabling them to compete successfully with the carbohydrate fermenters. Hobson and Wallace (1982), indicated that on feeding oxalate-rich feeds, the capacity of the rumen f l u i d to detoxify oxalate would increase with time so that otherwise l e t h a l doses of oxalate may be digested. In essence then, t h i s would mean that feeding rhubarb leaves would only be l i m i t e d by other n u t r i t i o n a l requirements and not by oxalate t o x i c i t y . The high s o l u b i l i t y and degradability of CP in rhubarb leaves and sweet potato vines could be associated . .44 with the high degradability of albumins and globulins. This is unfortunate in that albumins and globulins normally have a better balance of amino acids and a higher b i o l o g i c a l value than do prolamins and g l u t e l i n s (Clark et a l . , 1987). Banana leaves have high CP content (15%) and were highly undegradable. More information on the amino acid content and their a v a i l a b i l i t y in the small int e s t i n e s would be needed before establishing the amount of milk production that can be supported by feeding banana leaves to cows. Satter (1983) observed similar considerations in formulating diets on the basis of protein degradation. .45 SUMMARY AND CONCLUSIONS The rate constants and e f f e c t i v e degradation in the rumen for the various feedstuffs are given in the preceeding Tables. Green maize chop, fodder sorghum, bana grass and clone.13 variety had moderate to highly degradable DM and CP (50-60%). Together with kikuyu grass and trachyphyllum, these fodder grasses may have adequate protein supplies for a medium y i e l d i n g dairy cow. However nitrogen supplementation would be required as the grasses mature. Energy supplies would have to be evaluated. For the other grasses e f f e c t i v e DM and CP degradation were s i g n i f i c a n t l y (P<0.05) lower even at an early stage of growth. Lucerne, sweet potato vines and rhubarb leaves could provide the supplemental nitrogen during periods of deficiency. In view of their low rumen degradability, banana leaves and desmodium and/or wheat bran could supplement some of the energy and protein needs when either maize stover or Wheat straw are fed. Banana leaves and desmodium may not support high milk production. Attention must be given to th e i r amino acid content, a v a i l a b i l i t y of the undegraded protein and the "protein status of the l a c t a t i n g cows. Rhubarb leaves have a high rumen CP and DM degradability and, low ADF and NDF contents. A possible ration could . .46 i n c l u d e molasses, both as a source of r e a d i l y fermentable sugars and a l s o to improve p a l a t a b i l i t y . Maize s t o v e r c o u l d then be used to supply the f i b r e . Rhodes grass , red oats grass and s t a r g r a s s need to be supplemented with m a t e r i a l s of h i g h bypass p r o t e i n and low bulk. T h i s w i l l enable m i c r o b i a l u t i l i z a t i o n of these g r a s s e s . Wheat bran would be a s u i t a b l e f e e d s t u f f f o r t h i s purpose. Sweet potato v i n e s and l u c e r n e c o u l d u s e f u l l y supplement both fermentable p r o t e i n and energy a c r o s s the f e e d s t u f f s . Maize stover and wheat straw are l i m i t e d i n t h e i r u t i l i z a t i o n by t h e i r low CP c o n t e n t s and low DM d e g r a d a t i o n . Although milk p r o d u c t i o n w i l l be low when maize stover and wheat straw are fed to d a i r y c a t t l e , these f e e d s t u f f s c o u l d be used as a source of f i b r e . Green maize chop, fodder sorghum, n a p i e r g r a s s , kikuyu g r a s s , P. trachyphyllum, rhubarb l e a v e s , banana l e a v e s , sweet potato v i n e s , l u c e r n e and desmodium had moderate to high d e g r a d a b i l i t y . These f e e d s t u f f s t h e r e f o r e o f f e r a great p o t e n t i a l f o r c o n s e r v a t i o n . The p r o p o r t i o n of i n s o l u b l e p r o t e i n and i t s rumen de g r a d a t i o n r a t e has s i g n i f i c a n t i n f l u e n c e on the e f f e c t i v e d e g r a d a t i o n . Hence s o l u b i l i t y alone may not be a good i n d i c a t o r of p r o t e i n d e g r a d a b i l i t y . The d e c l i n e i n DM s o l u b i l i t y and e f f e c t i v e d e g r a d a b i l i t y with m a t u r i t y of forages c o u l d be a t t r i b u t e d to the gradual . .47 dominance of the stem tissue over the leaf tissue and an increase in the l i g n i f i e d s t r u c t u r a l polysaccharides. Proteins that have a low s o l u b i l i t y in the ruminal f l u i d and that contain extensive c r o s s - l i n k i n g , such as would be provided by the d i s u l f i d e bonds of g l u t e l i n s e.g in Wheat bran, are less accessible to the microbial p r o t e o l y t i c enzymes and r e l a t i v e l y r e s i s t a n t to degradation. To obtain optimum production in a dairy cow, there has to be adequate intake. Intake can be hampered by low rumen degradability. Low and slow degradability which may be caused by excessive l i g n i n l e v e l s or n u t r i t i o n a l d e f i c i e n c i e s reduces f i b r e digestion and results in poorer intakes. CP contents below 8% as was obtained with Maize stover, Wheat straw or the mature pasture grasses would be inadequate for maximum dairy production. However, during the dry season when dairy feeds are in short supply, a combination of the low qua l i t y roughages with protein and energy supplements could be used. This combination would not be expected to sustain high milk production. .48 CHAPTER 2. THE EFFECTS OF FORAGE PARTICLE LENGTH AND HEAT TREATMENT OF PROTEIN SOURCES ON INTAKE, MILK YIELD AND COMPOSITION AND RATION DIGESTIBILITY BY DAIRY CATTLE. INTRODUCTION With the onset of l a c t a t i o n a rapid increase in protein requirement arises which cannot be met by microbial protein alone. Feeding highly degradable proteins would supply i n s u f f i c i e n t amounts of amino acids to the intestines over t h i s period. Responses to additional undegradable protein in terms of increased milk y i e l d , milk fat and milk protein have been noted in l a c t a t i o n t r i a l s . Numerous factors influence ruminal degradation by a l t e r i n g microbial a c t i v i t y and access to feed components. Among the factors involved include retention time in the rumen, feed intake, protein s o l u b i l i t y , the extent of c r o s s l i n k i n g in the protein, and processing and storage e f f e c t s on protein. Canola meal and dehydrated a l f a l f a are used as protein supplements for dairy cows in Canada and some states in the P a c i f i c Northwest. Canola has been looked upon as a readily degradable protein source, while dehydrated a l f a l f a has moderate supplies of energy and protein. The l a t t e r i s also considered to be a good source of undegraded protein. Heat treatment decreases both the s o l u b i l i t y of protein and the rate of degradation of protein in the rumen. The treatment of good q u a l i t y proteins such as canola or dehydrated-alfalfa meal should allow adequate nitrogen to . .49 become available for maximum rumen microbial growth. It should also allow s i g n i f i c a n t amounts of the dietary protein to bypass ruminal degradation. Overall, the e f f i c i e n c y of u t i l i z a t i o n by the animal should be improved. Physical factors associated with p a r t i c l e size and p a r t i c l e s p e c i f i c gravity a f f e c t passage from the rumen. I n i t i a l mastication, microbial fermentation and rumination play a s i g n i f i c a n t role in roughage ingesta communition. Small p a r t i c l e s have greater surface area accessible to microbial attack and thereby increase digestion rate. Hence forage p a r t i c l e size w i l l have an e f f e c t on the rate at which material w i l l pass through the rumen as well as on the extent of digestion occurring within the rumen. By reducing the p a r t i c l e size of forage the amount of chewing required per unit of feed i s reduced. Milk fat content has also been found to be reduced. It i s expected then that t h i s reduced chewing means that material should be passing through the rumen with less requirement for physical breakdown. Supposedly more protein w i l l accompany t h i s dry matter from the rumen. This t r i a l had two objectives; a) To determine the e f f e c t of forage p a r t i c l e length on feed intake, milk y i e l d and composition, and ration d i g e s t i b i l i t y . b) To determine the e f f e c t of heat treatment of two protein sources on feed intake, milk y i e l d and composition, and ration d i g e s t i b i l i t y . . .50 LITERATURE REVIEW PROTEIN AND ENERGY FOR LACTATING DAIRY COWS. Output from a given l e v e l of protein intake i s dependent on energy supply; and vice versa, the amount of protein required to sustain a p a r t i c u l a r output depends on energy supply (Broster and Oldham, 1981). Further the two researchers have quoted some work which confirmed that energy intake does influence the milk output supported by a given amount of protein. Increasing energy supply had a greater e f f e c t on milk y i e l d than increasing protein. Paquay et a l . (1973) have estimated the optimal dietary ratios of metabolizable energy to protein. Too wide a r a t i o reduces milk y i e l d , while a narrow r a t i o i s not b e n e f i c i a l . In addition these researchers observed that the optimal r a t i o of protein to energy f e l l with increasing l e v e l of production. With the onset of l a c t a t i o n an increase in protein requirement arises which cannot be met by microbial protein alone (Orskov et a l . , 1981; E r f l e et a l . , 1983; Mahadevan et a l . , 1983). This i s thought to be so because the y i e l d of net amino acid nitrogen from microbial protein synthesis is i n s u f f i c i e n t to meet the net amino acid requirement for incorporation into milk protein. There are very few data in which increases in milk y i e l d have been obtained from feeding a source of protein with a low degradability to cows in . .51 energy balance or in marginally p o s i t i v e energy balance (Clark, 1975; Broderick, 1975). Since the microbial protein produced i s considered to be r e l a t i v e l y constant per unit of metabolizable energy (ME) (ARC, 1980; Orskov et a l . , 1981), there i s , t h e o r e t i c a l l y , a requirement for a less degradable protein as milk y i e l d increases. Experiments conducted to test t h i s hypothesis, using p r a c t i c a l milk production t r i a l s , have often f a i l e d to reveal any detectable change in milk y i e l d when proteins expected to have d i f f e r e n t degradability have been used (Kaufmann and Lupping, 1982; Orskov et a l • , 1981; Clay and Satter, 1979). If the cows are consuming ME in excess of th e i r requirement, then more microbial protein w i l l be a v a i l a b l e . This may occasionally mask responses to dietary protein (Kaufmann and Lupping, 1982). Orskov et a l • (1981) however noted that, what i s probably more important i s that the rate of outflow of protein from the rumen increases as the food intake increases. Even though intake has been recognized as a comparatively independent n u t r i t i o n a l a t t r i b u t e , most ordinary ration formulation programmes assume that a diet of higher net energy (NE) or d i g e s t i b i l i t y w i l l be consumed in greater amounts (Van Soest et a l . , 1984). Hence, i f the cows eat to th e i r ME requirement, then intake increases with increasing milk y i e l d . An increase in the f r a c t i o n a l outflow rate can thus make a substantial difference to the e f f e c t i v e degradability of the protein. Orskov et a l . (1981 ) termed . .52 t h i s as a self-compensating mechanism whereby an increase in intake leads to a lower degradability. Evidence exists i n d i c a t i n g that the e f f e c t i v e y i e l d of microbial protein increases with outflow rate. Cows in early part of l a c t a t i o n but, in negative energy balance respond by increasing t h e i r y i e l d of milk when they are given undegradable protein supplements (Orskov et a l . , 1981). Previously Orskov et a l . (1977) had i l l u s t r a t e d this in an experiment in which p o t e n t i a l l y high-yielding cows were offered ME to support only 10 Kg of fat corrected milk (FCM). The cows were then given either casein or glucose, abomasally. The cows given casein increased t h e i r milk fat and protein content, and also the milk y i e l d . Only when cows were r e s t r i c t e d in intake during early l a c t a t i o n , or given a diet which did not enable them to meet their protein need, did the animals respond to supplements of protected protein (Cressman et a l . , 1977; R o f f l e r et a l . , 1978). It would appear that protein stimulates milk y i e l d and thereby increases weight loss in early l a c t a t i o n , but a similar response i s not seen in mid and late l a c t a t i o n (Orskov et a l . , 1 981 ). Both the l e v e l of energy and protein in the diet a f f e c t protein content of milk. The l a t t e r does so only up to 18 percent protein content in the concentrate but not beyond (Broster and Oldham, 1981). Increases occur in a l l the major milk proteins, namely; casein, £>-lactoglobulin and D-. . 5 3 l a c t o a l b u m i n ( B r o d e r i c k , 1975). G e n e r a l l y p r o t e i n i n t a k e s around normal l e v e l s have l i t t l e e f f e c t on the p r o t e i n content of milk, but B r o s t e r and Oldham i n d i c a t e d t h a t any e x t r a d i e t a r y p r o t e i n may i n c r e a s e the NPN i n m i l k . I t i s t h e r e f o r e q u i t e apparent that i n p r a c t i c e i t i s energy supply r a t h e r than p r o t e i n supply which i n f l u e n c e s milk p r o t e i n c o n t e n t . Energy w i l l l i m i t milk p r o t e i n i f l e s s d i g e s t i b l e feeds and forages are used. T h i s problem e x i s t s f o r unsupplemented g r a z i n g animals on poor q u a l i t y p a s t u r e s , p a r t i c u l a r l y i n the t r o p i c s where l i t t l e c o n c e n t r a t e i s f e d , and f o r a g e s are of low q u a l i t y (Van Soest et a l . , 1984). Other experiments have shown that l a c t a t i n g cows w i l l respond to p o s t - r u m i n a l p r o t e i n i n f u s i o n s . C a s e i n i n f u s e d abomasally i n c r e a s e d the y i e l d of f a t c o r r e c t e d milk from 16 to 23 kg per day (Orskov, 1982). F i s h e r (1972) a l s o o btained improved milk p r o t e i n s e c r e t i o n with i n t r a v e n o u s methionine i n f u s i o n . The use of p r o t e c t e d p r o t e i n s improves the amino a c i d supply to the a n i m a l . I t a l s o decreases the s u r p l u s ammonia, thus reducing s t r e s s on l i v e r metabolism and hence improving c o n d i t i o n s f o r good f e r t i l i t y (Kaufmann and Lupping, 1982). Orskov (1982) i n d i c a t e s t h at the response to d i f f e r e n c e s i n p r o t e i n d e g r a d a b i l i t y depend very much on the extent of negative energy balance i n the cow. FORAGE DIGESTION. Formulation of h i g h forage d i e t s f o r h i g h - p r o d u c i n g cows should be based on a c c u r a t e e s t i m a t e s of d i g e s t i b i l i t y of the . . 54 d i e t as affected by intake, cost and amount of concentrates. Maximum u t i l i z a t i o n of forages by ruminants depend on active fermentation in the rumen. Negative associative effects have been recognized under varying supplementation programmes (Llano and De Peters, 1985; Hunt, 1985). It occurs when d i g e s t i b i l i t y of a feed mixture i s less than that of the sum of the individual components ( M i l l e r and Muntifering, 1985). The magnitude of any associative effects vary with the physical form of the d i e t , r a t i o of forage to concentrate and the q u a l i t y of forages. Plants produce compounds that provide among other things, a degree of protection against microbial invasion. Included in these protective compounds are l i g n i n , and the phenyl-propanoids associated with l i g n i n structure, tannins, cutin and s i l i c a (Van Soest, 1982; Jung and Fahey, 1983). The concentrations and form of these compounds in grains and grain by-products, as well as forages, may be p a r t i a l l y responsible for differences in fiber digestion among various feedstuffs. Age at which forages are harvested i s related to their n u t r i t i v e value. This i s explained by gradual dominances of stem tissue over leaf tissue and increased l i g n i f i e d s t r u c t u r a l polysaccharides associated with aging (Llano and De Peters, 1985). A negative r e l a t i o n s h i p between the degree of 1 i g n i f i c a t i o n and c e l l w a l l digestion in forages is well recognized (Van Soest, 1982). In addition to t h i s l i m i t a t i o n . .55 on f i b e r d i g e s t i o n by microbes, i t appears that the presence of the phenylpropanoid u n i t s , p-coumaric and f e r u l i c a c i d s , or t h e i r complexes with h e m i c e l l u l o s e and c e l l u l o s e a l s o reduce ruminal d i g e s t i o n (Hoover, 1986). Using h i g h q u a l i t y e a r l y cut hay reduced the amount of g r a i n s needed to a t t a i n a given T o t a l D i g e s t i b l e N u t r i e n t s (TDN) c o n c e n t r a t i o n as compared with l a t e cut hay (Llano and De P e t e r s , 1985). Jung and Fahey (1984) found the d e c l i n e i n f i b e r d i g e s t i o n i n mature a l f a l f a was a s s o c i a t e d with i n c r e a s e d l i g n i n , whereas d i g e s t i b i l i t y d e p r e s s i o n s i n t a l l fescue were a s s o c i a t e d with i n c r e a s e d c o n c e n t r a t i o n s of p-coumaric and f e r u l i c a c i d . In sorghum g r a i n s and i n forages, tannins have a l s o been shown to decrease m i c r o b i a l metabolism, i n h i b i t enzymes i n c l u d i n g c e l l u l a s e s and depress dry matter d i g e s t i o n (Kumar and Singh, 1984). A r e c i p r o c a l r e l a t i o n s h i p between s i l i c a and l i g n i n contents of forages has been observed, and d i g e s t i b i l i t y d e p r e s s i o n s are more c l o s e l y a s s o c i a t e d with the sum of l i g n i n and s i l i c a than with e i t h e r s i n g l e component (Hoover, 1986; Van Soest and Jones, 1968). C u t i n content v a r i e s markedly among f i b e r s o u r c e s . Hoover (1986) r e p o r t e d that i n t a c t c u t i c l e c o u l d cause a 6 to 48 hour l a g time in i n i t i a t i o n of d i g e s t i o n of p l a n t p a r t i c l e s . T h i s v a r i e d with p l a n t s p e c i e s and genotype. I t was r e p o r t e d a l s o that no d i g e s t i o n took p l a c e as long as" "the c u t i c l e remained i n t a c t . T h i s shows the importance of the i n t e r a c t i o n between chemical components and p h y s i c a l . .56 treatment of the p l a n t on d i g e s t i o n . S t u d i e s conducted by Pond et a l . (1984) found the d i s r u p t i o n of c u t i c u l a r m a t e r i a l by m a s t i c a t i o n and rumination to be a major f a c t o r a s s o c i a t e d with feed p a r t i c l e s i z e r e d u c t i o n . The above mentioned o b s e r v a t i o n s suggest t h a t p l a n t components can a l t e r c e l l w a l l d e g r a d a t i o n through p h y s i c a l b a r r i e r s i n c l u d i n g l i g n i n , c u t i n and s i l i c a . These f a c t o r s may be expressed as a l a g time phenomenon. Hoover (1986) i n d i c a t e d t h at the chemical e f f e c t s of phenylpropanoids and t a n n i n s on d e p r e s s i n g m i c r o b i a l a c t i v i t y appear to i n v o l v e i n h i b i t i o n of enzymes. These responses c o u l d be expressed both as l a g time and a decrease in r a t e of c e l l w a l l d i g e s t i o n . Forage p a r t i c l e s i z e and d i g e s t i o n . T y p i c a l l y forages make up the l a r g e s t p r o p o r t i o n of d a i r y f e e d s . The r e l a t i v e p r o p o r t i o n of forages to c o n c e n t r a t e s vary g r e a t l y . Maximum u t i l i z a t i o n of forages by the ruminant depend on a c t i v e m i c r o b i a l f e r m e n t a t i o n i n the rumen. T r a d i t i o n a l l y , the concept has been t h a t forages are roughages, e f f e c t i v e o n l y as a source of f i b e r to s t i m u l a t e rumination and maintain milk f a t ( F o s t e r and Woods, 1970). However, there i s a growing a p p r e c i a t i o n of the f e e d i n g value of h i g h q u a l i t y f o r a g e s . F i s h e r (1985) a t t r i b u t e d the supplementation of c e r e a l g r a i n s to a number of f a c t o r s : Amongst them i s the f a c t t h a t a higher n u t r i e n t d e n s i t y i s r e q u i r e d i n the e x p l o i t a t i o n of the g r e a t e r g e n e t i c p o t e n t i a l . .57 of the d a i r y cow. A l s o maximum milk p r o d u c t i o n has been assumed to be the optimum l e v e l of p r o d u c t i o n . S u b t l e d i f f e r e n c e s i n forage q u a l i t y e x i s t and have an e f f e c t on the response i n rumen d i g e s t i o n due to s p e c i f i c supplementation. R e s u l t s of some s t u d i e s suggest that the a d d i t i o n of r e a d i l y fermentable carbohydrates to a forage d i e t can, per se, cause a d e p r e s s i o n i n f i b e r d i g e s t i o n (Hoover, 1986). A l s o p h y s i c a l f a c t o r s a s s o c i a t e d with p a r t i c l e s i z e and p a r t i c l e s p e c i f i c g r a v i t y a f f e c t passage from the rumen (Welch, 1986). P a r t i c l e s i z e a c q u i r e s importance i n view of the need f o r rumen bypass n u t r i e n t s and the i n c r e a s i n g economic pr e s s u r e being p l a c e d on forage-based p r o d u c t i o n systems. Rumen res i d e n c e time and passage are important f a c t o r s i n the c o n t r o l of i n t a k e , d i g e s t i b i l i t y , p r o t e i n metabolism and p r o t e i n escape. I n i t i a l m a s t i c a t i o n , m i c r o b i a l f e r m e n t a t i o n , and rumination p l a y a r o l e i n roughage i n g e s t a communition (Welch, 1986). I t has been hy p o t h e s i z e d (Kerley et a l • , 1985; Pearce and Moir, 1964) that rumination i s the most important f a c t o r i n the r e d u c t i o n of p a r t i c l e s i z e . However i t i s d i f f i c u l t to determine the c o n t r i b u t i o n of each f a c t o r to the o v e r a l l p r o c e s s of r e d u c t i o n . S e l e c t e d stems from s e v e r a l d i f f e r e n t s p e c i e s and m a t u r i t i e s of hay showed v i r t u a l l y no change in p h y s i c a l form when s u b j e c t e d to the - rumen environment f o r 10 days in nylon bags (Welch, 1982)". Other r e s u l t s from the same resear c h e r showed t h a t lengths of p l a s t i c ribbon 7-cm long with a 0.90 s p e c i f i c g r a v i t y . .58 r e q u i r e d e x t e n s i v e rumination and p a r t i c l e s i z e r e d u c t i o n before they c o u l d pass from the rumen. Although p a r t i c l e s of 5 cm may pass through the r e t i c u l o -omasal o r i f i c e , Welch (1986) noted that most p a r t i c l e s l e a v i n g the rumen are s m a l l e r than 1 mm. T h i s has l e d to the idea of a c r i t i c a l p a r t i c l e s i z e (Poppi et a l . , 1980; K e r l e y et a l . , 1985). Poppi et a l . (1980) has r e p o r t e d that most p a r t i c l e s i n the p o s t - r u m i n a l g a s t r o i n t e s t i n a l t r a c t of sheep and c a t t l e pass a 1 . 1 8 mm s i e v e . The o r i g i n a l source of t h i s small p a r t i c l e p o p u l a t i o n i s the r e t i c u l o r u m e n . Smith et a l . (1967) found that p a r t i c l e s l e a v i n g the rumen of sheep a l l passed through a 0.84 mm s c r e e n . K e r l e y et a l . (1985) a l s o r e p o r t e d that d e s p i t e d i f f e r e n c e s among f o r a g e s , average d i g e s t a p a r t i c l e s i z e must approach approximately 600 to 700-nm before d i g e s t a w i l l pass from the rumen of sheep consuming forages ad l i b i t u m . Small p a r t i c l e s s i z e seems to be r e q u i r e d f o r passage from the rumen, but the exact mechanism that separates out the p a r t i c l e s i s s t i l l u n c l e a r . Welch (1986) has quoted some work where f i b e r o p t i c s was used to photograph the o r i f i c e i n c a t t l e . I t was found t h a t the maximum opening was more than 4 mm, thus making i t d i f f i c u l t t o e x p l a i n the s e p a r a t i o n by o r i f i c e a c t i o n . Small p a r t i c l e s have g r e a t e r s u r f a c e area a c c e s s i b l e to m i c r o b i a l a t t a c k and thereby i n c r e a s i n g d i g e s t i o n r a t e . K e r l e y et a l . (1985) i n d i c a t e s that the g r e a t e r e f f e c t of i n g e s t i n g small p a r t i c l e s i s that the r a t e of passage from . .59 the rumen i s i n c r e a s e d . Since rumen d i g e s t i o n i s the net r e s u l t of c o m p e t i t i o n between d i g e s t i o n and passage, any f a c t o r t h a t i n c r e a s e s passage r a t e s a l s o decreases the time a v a i l a b l e f o r m i c r o b i a l attachment to the d i g e s t a and, thus decreases rumen fe r m e n t a t i o n . E f f e c t of c o n c e n t r a t e s on d i g e s t i o n . D i f f e r e n c e s among forages, g r a i n s and by-products i n chemical and anatomical composition can a l t e r r a t e s of c e l l w a l l d e g r a d a t i o n by rumen microbes. T h i s may be r e s p o n s i b l e f o r p a r t of v a r i a t i o n i n d i e t dry matter i n t a k e by ruminants. Mertens and L o f t e n (1980) used the k i n e t i c s of forage d i g e s t i o n to e x p l a i n the decrease i n i n v i t r o d i g e s t i b i l i t y when s t a r c h i s added to d i e t s f o r ruminants. T h e i r o b s e r v a t i o n s were that the a d d i t i o n of s t a r c h i n c r e a s e d l a g time and decreased the p o t e n t i a l extent of f i b e r d i g e s t i o n . However they found i t u n l i k e l y that e i t h e r of the two e f f e c t s would e x p l a i n the d e p r e s s i o n i n f i b e r d i g e s t i o n i n v i v o . Since c e l l u l a s e i s s e n s i t i v e to a c i d i t y (Hungate, 1966), i t was suggested that the primary mechanism f o r the i n v i v o d e p r e s s i o n of f i b e r d i g e s t i o n a s s o c i a t e d with s t a r c h a d d i t i o n to the d i e t i s a r e d u c t i o n of c e l l u l o l y t i c a c t i v i t y by a c i d c o n d i t i o n s a s s o c i a t e d with r a p i d s t a r c h f e r m e n t a t i o n . Competition between passage and d i g e s t i o n f o r p o t e n t i a l l y d i g e s t i b l e f i b e r were a l s o a s s o c i a t e d with the d e p r e s s i o n of dry matter d i g e s t i b i l i t y when co n c e n t r a t e s are f e d . M i l l e r and M u n t i f e r i n g (1985) observed that f i b e r d i g e s t i b i l i t y . .60 depression i s mediated primarily through decreased potential extent of digestion; lag e f f e c t s and competition between digestion and passage did not appear to be s i g n i f i c a n t components of fiber d i g e s t i b i l i t y depression when grain i s fed. Measurement of ration d i g e s t i b i l i t y . Ration d i g e s t i b i l i t y could be measured through the conventional faecal c o l l e c t i o n method. However markers (both natural and external) offe r some d i s t i n c t advantages. Kotb and Luckey (1972) reviewed the use of markers in d i g e s t i b i l i t y studies. They concluded that markers offer the advantages of cheapness and convenience. Their review however did not s p e c i f i c a l l y consider the use of Acid-Insoluble Ash (AIA) as a d i g e s t i b i l i t y marker. Van Keulen and Young (1977) found the dry matter d i g e s t i b i l i t y c o e f f i c i e n t s estimated by the AIA marker method to be very close to the c o e f f i c i e n t s determined by the t r a d i t i o n a l t o t a l faecal c o l l e c t i o n method. Thonney et a l . (1979) compared AIA and permanganate l i g n i n as indicators to determine d i g e s t i b i l i t y of c a t t l e rations and found that AIA did not underestimate d i g e s t i b i l i t y determined by the t o t a l c o l l e c t i o n method s i g n i f i c a n t l y (P<0.001). Permanganate l i g n i n was found to underestimate d i g e s t i b i l i t y by 23.9%. PROTEIN SUPPLEMENTATION. The most successful attempts at improving rumen fermentation has been with protein supplementation (Hunt, . .61 1985). L l a n o and De P e t e r s (1985) observed that although high i n t a k e depressed d i g e s t i b i l i t y f o r v a r i o u s f o r a g e s , lower d e p r e s s i o n s were a s s o c i a t e d with legumes. C e l l u l o l y t i c b a c t e r i a are s t r i c t l y anaerobic and most of them r e q u i r e ammonia as the n i t r o g e n source. T h e i r growth r a t e i s a l s o dependent on the presence of branched-chain f a t t y a c i d s such as i s o b u t y r a t e and i s o v a l e r a t e and 2-methylbutyrate (Orskov, 1982). These products r e s u l t from the deamination of v a l i n e , l e u c i n e and i s o l e u c i n e r e s p e c t i v e l y . A h i g h requirement f o r amino a c i d s or p e p t i d e s has a l s o been found f o r a m y l o l y t i c organisms (Hungate, 1966). Hence the c o m p e t i t i o n between f i b r o l y t i c and n o n - f i b r o l y t i c organisms f o r n i t r o g e n c o n t a i n i n g compounds under c o n d i t i o n s of l i m i t i n g a v a i l a b l e p r o t e i n may a f f e c t ammonia requirements. Supplementation with p r o t e i n s would be s u p e r i o r to other NPN's i n m a i n t a i n i n g f i b e r d i g e s t i o n . Hoover (1986) has quoted some work where amino a c i d s improved growth on an ammonia medium of a c e l l u l o l y t i c b a c t e r i a . C u r r e n t f e e d i n g p r a c t i c e s f o r l a c t a t i n g c a t t l e which; encourage r a p i d rumen turnover through hi g h feed i n t a k e , and which a l s o i n c l u d e ample s t a r c h and low s o l u b l e p r o t e i n , may p o s s i b l y cause reduced o r g a n i c matter d i g e s t i o n . T h i s would occur p r i m a r i l y through e f f e c t s on s u p p r e s s i o n of f i b r o l y t i c organisms. High rumen fermentable carbohydrates would encourage r a p i d growth of a m y l o l y t i c microbes that r e q u i r e amino a c i d s and p e p t i d e s . T h i s i n turn would l i m i t . .62 a v a i l a b i l i t y of amino acids and ammonia nitrogen required for f i b r o l y t i c microbes. Under these conditions, ammonia requirements may exceed 3-8 mg percent (Kaufmann and Lupping, 1982), and there may be a higher requirement for amino or isoacids. Canola meal and dehydrated a l f a l f a as protein supplements. Canola meal derived from the crush of canola seed, is used as a protein supplement for livestock in Canada and some states of the P a c i f i c Northwest. Canola i s a genetic c u l t i v a r of rapeseed, which was f i r s t introduced into Canada around 1936 for i t s o i l ( B e l l , 1984). Rapeseed i s high in erucic acid and glucosinolates, and feeding high l e v e l s of the meal to monogastric animals reduced diet p a l a t a b i l i t y and animal performance (De Peters and Bath, 1985). Canola meal could be used as the sole protein source in the diet of l a c t a t i n g cows without adverse e f f e c t s on feed intake, milk y i e l d or composition ( B e l l , 1984). The glucosinolates or more s p e c i f i c a l l y t h e i r hydrolytic products, have goitre-producing properties ( B e l l , 1984; Sanchez and Claypool, 1983). More pronounced glucosinolate breakdown and greater g o i t r o g e n i c i t y seems to result from the addition of myrosinase to the diet ( B e l l , 1984). Thyroid function in la c t a t i n g cows, in response to rapeseed meal feeding, has been assessed by the administration of thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH). The high glucosinolate rapeseed meal (HG-RSM) . .63 caused incresed TSH l e v e l s , whereas low glucosinolate rapeseed meal (LG-RSM) resulted in no change from the normal ( B e l l , 1984). B e l l also found increased thiocynate levels in milk and reduced iodine levels in blood and milk. By 1981, two "double low" rapeseed c u l t i v a r s namely Brassicca napus and B. campestris had been produced in Canada. These were low in both erucic acid and glucosinolates. The name 'Canola' was adopted in 1979 to apply in Canada to a l l "double low" c u l t i v a r s . Crushed canola seed yie l d s approximately 40% o i l and 57% meal of which 35-39% i s protein ( B e l l , 1984; Sanchez and Claypool, 1983). The canola meal used as a protein supplement in livestock diets i s usually a mixture of the two "double low" c u l t i v a r s (Bell and J e f f e r s , 1976) and contains less than 3 mg of glucosinolates per gram (Sanchez and Claypool, 1983). A Canada-wide survey conducted by B e l l and J e f f e r s (1976) showed that a t y p i c a l canola sample contained 7.0 mg per gram of glucosinolates. This was attributed to inadequate cleaning to grade standards. Such high lev e l s of glucosinolates would show more potential e f f e c t on the feeding value of canola than any other feed component. Sharma et a l • (1977) observed that including Tower rapeseed (a double low c u l t i v a r ) at 25% of the grain mixture did not decrease t o t a l dry matter intake by Hostein cows. However, Waldern (1973) reported a s i g n i f i c a n t reduction in grain consumption by the dairy cows when commercial rapeseed . .64 meal was fed at 27% of the grain mix or 11.8% of the t o t a l dry matter intake. No reduction in grain consumption or silage dry matter intake by dairy cows was reported by Fisher and Walsh (1976) when a double zero rapeseed meal was included at 0, 11 or 22% l e v e l s of the grain mixtures. This difference may be related to a v a r i a t i o n in the glucosinolate content of the various meals used. Fisher and Walsh (1976) observed a s i g n i f i c a n t reduction in milk y i e l d , butterfat, protein and lactose contents and the t o t a l production of the milk constituents. They included 22 and 34% rapeseed meal in the grain mixtures. Sharma et a l . (1977) observed no s i g n i f i c a n t difference (P>0.05) in the same parameters mentioned above, when 25% of the grain mixture was comprised of canola meal. The discrepancies in the two results were a t t r i b u t e d to either the higher o i l content and/or reduced feed intake of the rations containing 22 and 34% canola meal. The above results show that canola meal can be fed at a l e v e l of 13% of the t o t a l d i e t dry matter or 26% of the concentrate dry matter in early l a c t a t i o n with no p a l a t a b i l i t y problems. A l f a l f a (Medicago sativa) o f f e r s a source of supplemental feed which may supply moderate amounts of both degradable protein with a balanced amino acid p r o f i l e and soluble carbohydrates. Some work quoted by Hunt (1985) showed that lambs fed wheat straw supplemented with dehydrated . .65 a l f a l f a had a greater dry matter intake compared with lambs supplemented with soybean meal. Heifers fed only ground and pellete d sun-cured a l f a l f a gained weight s i g n i f i c a n t l y faster than the heifers fed only pell e t e d dehydrated a l f a l f a meal (Dinius et a l . , 1975). Other observations made were that heifers fed sun-cured a l f a l f a required less feed per unit of gain than those fed dehydrated a l f a l f a meal. Heat Treatment of P r o t e i n Supplements. Treatment of a good qua l i t y protein such as canola or dehydrated a l f a l f a with heat, should allow adequate nitrogen to become available for maximum rumen microbial growth. It should also allow s i g n i f i c a n t amounts of the dietary protein to bypass ruminal degradation. Thus the e f f i c i e n c y of u t i l i z a t i o n by the animal should be improved. Numerous approaches have been used to enhance the resistance of dietary protein to proteolysis and deamination in the rumen e.g treating with; heat (Tagari et a l . , 1962; Mir et a l . , 1984; Stern et a l . , 1985), tannic acid (Nishimuta et a l . , 1974) formaldehyde (Nishimuta et a l . , 1974;) and with blood meal (Mir et a l . , 1984). Heat treatment of grains and forages s u b s t a n t i a l l y decreased s o l u b i l i t y of proteins (Nishimuta et a l . , 1974; Tagari et a l . , 1962) and the rate of degradation of protein in the rumen (Mir et a l . , 1984). The heating"that occurs during processing could reduce ruminal degradation. Although i t i s important that temperature and heating durations be . .66 a p p r o p r i a t e , optimal c o n d i t i o n s are o f t e n unknown (Stern e_t a l . , 1985). Overheating c o u l d r e s u l t i n the f a i l u r e of the p r o t e i n to be fermented i n the rumen or being d i g e s t e d i n the abomasum. Mir et a l . (1984) heated both soybean and canola at two l e v e l s , that i s , 110°C f o r 2 hours and 120°C fo r 20 minutes. They found that at e i t h e r of the two h e a t i n g l e v e l s p r o t e i n d e g r a d a t i o n f o r c a n o l a meal was s i g n i f i c a n t l y reduced (P<0.05). These r e d u c t i o n s i n p r o t e i n d e g r a d a b i l i t y were r e f l e c t e d by the decrease i n both the r a t e of ruminal d e g r a d a t i o n and a l s o i n the s o l u b l e f r a c t i o n of the p r o t e i n . T h e i r r e s u l t s agreed with those of Lindberg et a l . (1982). T h i s c o u l d t h e r e f o r e suggest t h a t c a n o l a p r o t e i n i s more r e a d i l y denatured by heat than i s soybean meal p r o t e i n . Work quoted by S a t t e r (1986) showed t h a t l a c t a t i n g cows fed d i e t s c o n t a i n i n g 65% g r a i n mix absorbed more amino a c i d s from the i n t e s t i n e s when the d i e t c o n t a i n e d a l f a l f a with 12.9% A c i d Detergent I n s o l u b l e N i t r o g e n (ADIN) than when a more normal amount of 8 to 10% was present i n the a l f a l f a . E n s i l e d forages may undergo e f f e c t i v e heat treatment at temperatures as low as 40 to 45°C, p r o v i d e d the temperature i s s u s t a i n e d f o r 3 months or more (Merchen and S a t t e r , 1983). M o i s t u r e , q u a n t i t y of s o l u b l e carbohydrates p r e s e n t , and maximum temperature are some of the f a c t o r s t h a t determine e f f e c t i v e n e s s of heat i n p r o t e c t i n g p r o t e i n from degradation in the rumen. A l f a l f a d e h y d r a t i o n occurs at a r e l a t i v e l y high . .67 temperature for a short duration (Goering, 1976). The net resul t could be similar to overheating, v i z , decreased animal performance. Goering (1976) observed that overheating of dehydrated a l f a l f a may be caused by overdrying; that i s , as long as the feed p a r t i c l e has water evaporating from i t , the temperature of the p a r t i c l e w i l l be less than 100°C, and overheating or damage w i l l be s l i g h t . When the p a r t i c l e i s almost dry and the a i r temperature around i t i s much higher, then the p a r t i c l e would probably overheat. The damage to the protein appears to involve the non-enzymatic browning reactions. Water, low pH and heat are involved in these reactions, however the net reaction is a condensation of carbohydrate degradation products with protein (Van Soest, 1962). Van Soest also indicated that below 80°C, non-enzymatic browning reactions have only s l i g h t e f f e c t s on the s o l u b i l i t y of the forage protein. Knipfel et a l . , (1983) observed that dry heating of a l f a l f a at 105°C for up to 1440 min resulted in a reduction of in v i t r o organic matter d i g e s t b i l i t y by rumen microbes. Increases in Acid Detergent Insoluble Nitrogen (ADIN) and Neutral Detergent Fibre (NDF) were also observed. .68 MATERIALS AND METHODS Animals. Twenty four l a c t a t i n g dairy cows in mid to early lac t a t i o n were used. The f i r s t group of cows was allocated to the canola rations. This group consisted of twelve top milk producing cows from the selected herd of 24 animals. Their average liveweight and milk y i e l d per day was 601.8 s.e 21.2 and 30.45 s.e 2.36 kgs respectively. Group two was allocated to the a l f a l f a rations. The average liveweight and milk y i e l d per day was 573.3 s.e 33.8 and 22.7 s.e 1.96 kgs respectively. A l l animals were balanced for i n i t i a l production and then allocated randomly to each treatment within groups, five animals in the a l f a l f a treatment were later dropped from the experiment. This took place at the beginning of period three. Feeds. Orchard grass hay was chopped at two cut lengths to give weighted mean p a r t i c l e lengths of 14.19 and 1.71 mm. Heat treatment was done by moist heating in trays (500 kgs. capacity) in a closed draught oven at 125°C oven temperature for 2 hours to atta i n 80-85°C internal feed temperature. The feed was then allowed to cool to room temperature prior to mixing. Ration Formulation. The concentrates were then made up based on either canola meal or dehydrated a l f a l f a meal (see appendix 1). . .69 Design. Each p r o t e i n source was s t u d i e d i n combination with e i t h e r short (SH) or long (LH) chopped orchard grass hay. A 4*4 L a t i n Squares was employed, with four p e r i o d s of 28 days d u r a t i o n and a 7 day a d a p t a t i o n i n t e r v a l between the p e r i o d s f o r each p r o t e i n source. The four treatments were set up as shown i n Appendix 2. A l l r a t i o n s were o f f e r e d at 40:60 forage to con c e n t r a t e r a t i o . Records and Sample Analysis. A l l cows were weighed every two weeks a f t e r the morning m i l k i n g . M i l k p r o d u c t i o n and feed intake were recorded d a i l y . Feed was o f f e r e d ad l i b i t u m with a small amount of weighback (<10%) being present d a i l y . Weighback and feed samples were taken every week. A composite (500g) sample was then obtained f o r each treatment i n a p e r i o d . As w e l l , a minimum of f i v e hay and feed samples (1-2 kg) were obtained i n the l a s t week of each p e r i o d f o r p a r t i c l e s i z e d e t e r m i n a t i o n . Composite milk samples f o r composition a n a l y s i s were taken from the two m i l k i n g s (morning and evening) on the l a s t day of the p e r i o d . M i l k i n g was done twice i n a day, w i t h i n an i n t e r v a l of 12 hours. A minimum of four "Grab" samples of the faeces per cow were obtained i n the l a s t week of each experimental p e r i o d . F a e c a l samples f o r cows i n the same group were composited to . .70 give a single sample. Chemical analysis, CP, ADF, NDF (see Chapter One for methods), including Acid Insoluble Ash (Van Keulen and Young, 1977) and ADIN (Goering and Van Soest, 1970) was done on the composited faecal and feed samples. A l l concentrates were tested for rumen degradability and s t a t i s t i c a l differences as set out in Chapter one. A 4(protein supplements) * 6(Incubation intervals) f a c t o r i a l arrangement in a completely radomized design was used for each protein concentrate. The incubation periods used were 1, 6, 12, 18, 24 and 36 hours. .71 RESULTS Feed composition. Table 7 shows the composition of the feedstuffs used. The concentrates were r e l a t i v e l y isonitrogenous. A l f a l f a rations were higher in both ADF and NDF content than canola rations. Table 7: Composition of the ration feedstuffs. Ration component: Nu t r i t i o n a l composition (%). CP ADF NDF ADIN* OC 12.35 8.56 18.54 0. 157 HC 12.25 9.20 20.22 0. 1 77 OA 13.01 17.71 25.84 0. 1 96 HA 12.65 18.65 27.09 0.209 Orchard grass hay 14.03 39.87 55.57 S.E.M 0.32 5.67 6.72 0.011 Complete ration base**: AI A OC 12.77a 21.79a 33.65 1 .76a HC 13.07ba 21.57a 34.95 1 .78a OA 14.05b 27.33b 37.86 1 .82a HA 13.60b 28. 18b 38.24 1 .92a S.E.M 0.28 1 .76 1.12 0.04 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05) *%ADIN as a fraction of dry sample weight. **Nutrient composition values were calculated on the basis of the feed consumed. Degradability of canola and a l f a l f a concentrates. After 24 hours of incubation, a s i g n i f i c a n t proportion of the concentrates DM and CP had been degraded in the rumen. There were sl i g h t increases in DM degradability as the experimental period progressed (Table 8). Heat treating ..72 canola meal resulted in s i g n i f i c a n t (P<0.05) decrease in the DM and CP degradability (Table 9). Both incubation time and heat treatment affected DM and CP degradability of a l f a l f a and canola concentrates s i g n i f i c a n t l y (P<0.05). Heat treated rations were s i g n i f i c a n t l y less degradable in the rumen than the unheated ones (Table 9). The degradation rate constants shown in Table 10 were calculated from Figures 5,6,7 and 8. Table 8: Mean extent of DM and CP degradation over the experimental duration - i n s i t u . Mean extent of degradation Period DM CP 1 63.23a 46.57a 2 66.08b 47.96a 3 66.81b 50.81a 4 64.45ab 52.29a S.E.M 0.81 1.30 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). Table 9: Mean extent of DM and CP degradation for canola and a l f a l f a based concentrates - i n s i t u . Ration treatment: Mean extent of degradation DM CP Unheated canola 66.91a 52.14a Heated canola 63.38b 46.67b Unheated a l f a l f a 59.35a 46.52a Heated a l f a l f a 54.59b 42.01b S.E.M 2.65 2.07 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). . .73 Fig 5: % Degradation Vs Rumen Incubation Time. Canola canaanfe-atas —[DM]. 100 D Heated Canola. Time Incubated in the rumen [hrs]. + Unheated Canola. 74 b F i g 6: 96 Degradation Vs Rumen incubation Time. Canola oanosntratea —[CP]. 100 • Heated Canola. Time Incubated in the rumen [hrs]. + Unheated Canola. .75 F i g 7: 100 % Degradation Vs Rumen Incubation Time. Alfalfa Concentrates [DU]. 90 -4 80 -4 76 % Degradation Vs Rumen Incubation Time. Alfalfa Concentrates [CP]. 10 20 —r~ 30 Heated Alfalfa. Time Incubated in the rumen [hrs]. + Unheated Afalfa. 77 Table 10: Degradation rate constants of canola and a l f a l f a concentrates. Degradation constant Feed constituent DM CP Unheated canola cone. a 46.66 1 6.66 b 30.00 61.11 c 11.10 7.50 Heated canola cone. a 38.88 11.11 b 34.45 58.89 c 9.49 6.30 Unheated a l f a l f a cone. a 45.55 23.33 b 24.45 40.00 c 6.90 4.80 Heated a l f a l f a cone. a 37.77 15.55 b 27.78 45.56 c 5.11 4.10 a= % s o l u b i l i t y , b= p o t e n t i a l l y degradable fractio n c= degradation rate constant [%/hr]. D i g e s t i b i l i t y and m i l k composition from c a n o l a based r a t i o n s . Acid insoluble ash (AIA) was used as an internal feed marker. A 93% recovery rate (Thonney et a l . , 1979) was used in the d i g e s t i b i l i t y calculations that followed. The model f i t t e d to explain the DM d i g e s t i b i l i t y was s i g n i f i c a n t at (P<0.05) and had an R-squared value of 0.61. Changes over the experimental period s i g n i f i c a n t l y (P<0.05) affected the DM d i g e s t i b i l i t y . DM d i g e s t i b i l i t y in period three was s i g n i f i c a n t l y (P<0.05) higher than the other periods (Table 11). Combining heated canola with short chopped hay s i g n i f i c a n t l y (P<0.05) reduced DM d i g e s t i b i l i t y . .78 (Table 12). Crude P r o t e i n d i g e s t i b i l i t y was e x p l a i n e d u s i n g a model with an R-squared value of 0.47. T h i s model was s i g n i f i c a n t at (P<0.05). CP d i g e s t i b i l i t y was s i g n i f i c a n t l y (P<0.05) higher i n p e r i o d three than i n the other experimental p e r i o d s (Table 11). Feeding heated can o l a c o n c e n t r a t e s together with short chopped hay s i g n i f i c a n t l y (P<0.05) reduced CP d i g e s t i b i l i t y (Table 12). ADF d i g e s t i b i l i t y was e x p l a i n e d using a model that accounted fo r 47% of the t o t a l v a r i a t i o n . T h i s model was s i g n i f i c a n t at (P<0.05). P r o t e i n treatment and hay chop l e n g t h d i d not s i g n i f i c a n t l y (P<0.05) a f f e c t the ADF d i g e s t i b i l i t y . P e r i o d two had a s i g n i f i c a n t l y (P<0.05) lower ADF d i g e s t i b i l i t y than a l l the others (Table 11). The model f i t t e d to e x p l a i n the v a r i a t i o n due to NDF d i g e s t i b i l i t y was s i g n i f i c a n t at (P<0.01) and accounted f o r 99.9% of the v a r i a t i o n . However, the c a l c u l a t i o n s f o r NDF d i g e s t i b i l i t y were based on p e r i o d two o n l y . Both canola and a l f a l f a r a t i o n s were f i t t e d i n the model. A l l canola treatments had s i g n i f i c a n t l y (P<0.01) d i f f e r e n t NDF d i g e s t i b i l i t y (Table 12). Rations with heated can o l a had lower NDF d i g e s t i b i l i t y than unheated canola based r a t i o n s . Short chopped hay s i g n i f i c a n t l y (P<0.05) reduced NDF d i g e s t i b i l i t y . V a r i a t i o n due to d a i l y intake was e x p l a i n e d by a model s i g n i f i c a n t at (P<0.05), and with an R-squared value of 0.28. . .79 Heat treatment of canola protein reduced the animals da i l y intake s i g n i f i c a n t l y (P<0.05) (Table 13). As the experimental period progressed, the d a i l y feed intake s i g n i f i c a n t l y (P<0.05) declined (Table 11). Hay chop length did not have a s i g n i f i c a n t e f f e c t on the animals voluntary feed intake. There was a s i g n i f i c a n t reduction in liveweight gain afte r period one. As the experiment progressed there was a s l i g h t , but not s i g n i f i c a n t reduction in the liveweight changes. Heat treatment and hay chop length did not affect t o t a l milk production s i g n i f i c a n t l y . Total milk y i e l d declined during the experiment (Table 14). These res u l t s were obtained from a model f i t t e d to explain the variation due to milk y i e l d . This model was s i g n i f i c a n t at (P<0.05) and had an R-squared value of 0.23. The fat content of the milk was s i g n i f i c a n t l y (P<0.05) reduced by the heat treatment of canola meal (Table 15). Out of the t o t a l v a r i a t i o n due to milk fat, 23% was explained by the model f i t t e d . This was s i g n i f i c a n t at (P<0.05). Heated canola treatments resulted in s i g n i f i c a n t l y (P<0.05) lower milk protein content than the unheated rations (Table 15). Total milk protein declined s i g n i f i c a n t l y over the experimental duration (Table 14). The models f i t t e d for the two effects above, were s i g n i f i c a n t (P<0.05) and had R-squared values of 0.24 and 0.25 respectively. Total milk lactose however, declined s i g n i f i c a n t l y . .80 between the f i r s t and the la s t two periods (Table 14). The models f i t t e d to account for the variations due to milk lactose were s i g n i f i c a n t at (P<0.05) and had R-squared values Table 11: D i g e s t i b i l i t y and d a i l y feed intake of canola based rations. Period D i g e s t i b i l i t y Voluntary Intake (Prd) DM CP ADF (g/kg Met.body wt) 1 66.71a 70.42a 32.10a 159.01a 2 65.82a 71.35a 17.99b 154.51ab 3 71.36b 74.36b 31.93a 148.39ab 4 66.1Oa 70.68a 29.52a 142.20b S.E.M 1 .30 0.91 3.35 3.66 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). Table 12: DM and CP d i g e s t i b i l i t y c o e f f i c i e n t s of canola based rations. Canola ration D i g e s t i b i l i t y c o e f f i c i e n t (%). DM CP NDF* ADF OC+LH 67. 94a 71 . 57a 38. 1 0a 30. 18a OC+SH 68. 25a 73. 1 8a 31 . 35b 28. 42a HC+LH 69. 65a 72. 73a 27. 79c 26. 71a HC+SH 64. 22b 69. 33b 20. 9ld 26. 23a S.E.M 1 . 16 0. 86 3. 58 0. 90 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). *Only period two values were included. Table 13: Daily feed intake of canola meal treatments. Ration treatment: Daily feed intake (g/kg met.body wt). Unheated canola 155.31a s. e 2.81 Heated canola 146.75b s.e 3.11 Long chop hay 150.38c s. e 3.11 Short chop hay 151.67c s. e 2.82 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). . .81 Table 14: Milk y i e l d (Yld) and composition over the experimental duration - Canola based rations. Prd Milk Yld. Milk composition (kg) Fat(%) Protein(%) Protein(kg) Lactose(%) 1 22.45a 2.82a 3.1 5a 0.85a 4.88ab 2 19.94ab 2.66a 3.12a 0.76ac 4.89b 3 17.63b 2.75a 3.12a 0.68bc 4.68a 4 16.62b 3.08a 3.25a 0.62b 5.06b S.E.M 1 .30 0.09 0.03 0.05 0.08 Values with d i f f e r e n t l e t t e r s are di f f e r e n t at (P<0.05). Table 15: Effects of canola ration treatments on milk y i e l d and composition. Ration Milk Yld. Milk composition. (kg) Fat(%) Protein(%) Prote in(kg) Lactose(%) OC 20.35a 3.11a 3.26a 0.76a 4.95a HC 17.95a 2.56b 3.06b 0.70a 4.80a S.E.M 1 .20 0.28 0.10 0.03 0.08 LH 19.57a 2.82a 3.20a 0.76a 4.95a SH 18.75a 2.83a 3. 13a 0.70a 4.80a S.E.M 0.41 0.005 0.035 0.03 0.08 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). Table 16: D i g e s t i b i l i t y of a l f a l f a based rations. Period D i g e s t i b i l i t y c o e f f i c i e n t (%). DM CP ADF 1 66.77a 70.42a 32.10a 2 65.70a 71.24a 27.61b 3 71.36b 74.36b 31.93a 4 67.15a 71.61a 32.91a S.E.M 1 .24 0.85 1 .20 Values with d i f f e r e n t l e t t e r s are d i f f e r e n t at (P<0.05). . . 8 2 Table 17: DM and CP d i g e s t i b i l i t y of a l f a l f a treatments. Treatment D i g e s t i b i l i t y c o e f f i c i e n t (%). DM CP NDF* ADF OA+LH 67. 94a 71 . 57a 20 . 23a 30. I8ab OA+SH 69. 29a 74. 1 2b 24 • 69b 31 . 81b HA+LH 69. 53a 72. 62ab 22 .88c 26. 33a HA+SH 64. 22b 69. 33c 20 .22a 26. 23a S.E.M 1 . 23 1 . 01 1 .09 1 . 40 Values with d i f f e r e n t l e t t e r s are di f f e r e n t at (P<0.05). *Only period two values were included. Table 18: Daily feed intake and ADF d i g e s t i b i l i t y . Treatment Voluntary feed intake (g/kg met.wt) Unheated a l f a l f a 156.76a s.e 2.87 Heated a l f a l f a 146.59b s. e 3.00 Long chop hay 150.22a s. e 3.00 Short chop hay 153.13a s. e 2.87 Values with d i f f e r e n t l e t t e r s are di f f e r e n t at (P<0.05). Table 19: Milk y i e l d and composition for a l f a l f a treatments. Prd Milk Yld. Milk composition (kg) Fat(%) Fat(kg) Lactose(%) Protein(kg & %) 1 19.39a 4.11a 0.78a 4.84a 0.63b 3.33ab 2 17.08ab 3.81a 0.67ab 4.87abc 0.59ab 3.39ab 3 15.78b 4.1 3a 0.64b 4.70b 0.54a 3.46b 4 14.47b 2.92b 0.52b 5. 1 2c 0.54a 3.1 5a S.E.M 1 .05 0.28 0.05 0.09 0.02 0.07 Values with d i f f e r e n t l e t t e r s are di f f e r e n t at (P<0.05). .83 Table 20: Milk y i e l d and composition of a l f a l f a treatments. Treat - Milk Y l d . Milk composition ment (kg) Fat (% & kg) Protein ( % & kg) Lactose(%) OA 14.92a 3.54a 0.56a 3.34a 0. 53a 4.74a HA 18.44b 3.93a 0.74b 3.31a 0.61b 5.03b S .E .M 1 .76 0.20 0.09 0.02 0.04 0.15 LH 17.20a 3.96a 0.68a 3.38a 0. 58a 4.87a SH 16.15a 3.53b 0.61a 3.29a 0.56a 4.91a S .E .M 0.53 0.22 0.04 0.05 0.01 0.02 Values with d i f ferent l e t t e r s are d i f f erent at (P<0.05). of 0.35 and 0.27 re spec t ive ly . D i g e s t i b i l i t y and milk composition of a l f a l f a based r a t i o n s . DM d i g e s t i b i l i t y was similar in the other periods except period three (Table 16). Ration combinations based on long chop hay had similar levels of DM d i g e s t i b i l i t y . However, heated a l f a l f a combined with short chop hay resulted in a si g n i f i c a n t (P<0.05) reduction in DM d i g e s t i b i l i t y of the ration (Table 17). These e f f e c t s were observed in a model f i t t e d to explain DM d i g e s t i b i l i t y . The model was s i g n i f i c a n t (P<0.05) and accounted for 66% of t o t a l v a r i a t i o n . CP d i g e s t i b i l i t y of a l f a l f a rations was s i g n i f i c a n t l y higher in period three than in the other experimental periods. Variation due to CP d i g e s t i b i l i t y was explained by a model s i g n i f i c a n t at (P<0.05) and with an R-squared value of 0.54. Further observations revealed that combining short chopped hay with unheated a l f a l f a increased CP d i g e s t i b i l i t y . .84 s i g n i f i c a n t l y (Table 17). Long chopped hay fed together with heated a l f a l f a had a s i m i l a r (P<0.05) high CP d i g e s t i b i l i t y to the unheated a l f a l f a d i e t s . A combination of heated a l f a l f a and short chopped hay r e s u l t e d i n a s i g n i f i c a n t l y (P<0.05) lower CP d i g e s t i b i l i t y . From the model f i t t e d to e x p l a i n ADF d i g e s t i b i l i t y , i t was observed that p e r i o d two had s i g n i f i c a n t l y lower val u e s (Table 16). Heating a l f a l f a r e s u l t e d i n lower (P<0.05) ADF d i g e s t i b i l i t y (Table 18). T h i s model had an R-squared value of 0.62 and was s i g n i f i c a n t at (P<0.01). Chopped hay fed together with unheated a l f a l f a based c o n c e n t r a t e r e s u l t e d i n s i g n i f i c a n t l y higher NDF d i g e s t i b i l i t y than a l l the other r a t i o n s (Table 17). Unheated a l f a l f a + long chop hay and, heated a l f a l f a + s h o r t chop hay had s i m i l a r (P<0.05) but low NDF d i g e s t i b i l i t y . Feeding heated a l f a l f a with long chop hay r a i s e d NDF d i g e s t i b i l i t y s i g n i f i c a n t l y (P<0.05). The model f i t t e d to e x p l a i n NDF d i g e s t i b i l i t y i s e x p l a i n e d i n the canola s e c t i o n above. The model f i t t e d to e x p l a i n the d a i l y feed intake showed that heat t r e a t i n g a l f a l f a reduced intake s i g n i f i c a n t l y (P<0.05) (Table 18). In the model, R< was equal to 0.30 at (P<0.05) s i g n i f i c a n t l e v e l . Liveweight gain was a f f e c t e d by the experimental p e r i o d (P<0.10). Although animals gained weight throughout the experimental p e r i o d , there was a r e d u c t i o n i n the r a t e of gain up to the f o u r t h p e r i o d . . .85 Heat t r e a t i n g a l f a l f a p e l l e t s r e s u l t e d i n s i g n i f i c a n t i n c r e a s e s i n milk p r o d u c t i o n (Table 20 ) . There was a l s o a s i g n i f i c a n t (P<0.05) d e c l i n e i n milk y i e l d as the experimental d u r a t i o n progressed (Table 19). Hay p a r t i c l e l e n g t h 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 t o t a l milk produced (Table 20 ) . The above r e s u l t s were based on a model s i g n i f i c a n t at (P<0.05) and with an R( of 0.38. The s i g n i f i c a n t l y lower b u t t e r f a t content i n p e r i o d four was a l s o r e f l e c t e d i n the t o t a l p e r i o d milk f a t p r o d u c t i o n (Table 19). Feeding d i e t s based on heated a l f a l f a s i g n i f i c a n t l y (P<0.05) r a i s e d the t o t a l milk f a t p r o d u c t i o n . Heat treatment of a l f a l f a d i d not however, i n f l u e n c e the b u t t e r f a t content (Table 20 ) . M i l k f a t content was higher (P<0.05) with long chop a l f a l f a hay d i e t s . The models f i t t e d to e x p l a i n b u t t e r f a t content and i t s t o t a l y i e l d were s i g n i f i c a n t at (P<0.05) and had R( values of 0.43 and 0.46 r e s p e c t i v e l y . Heating a l f a l f a p r o t e i n (Table 20) i n c r e a s e d the t o t a l p r o t e i n content of the milk s i g n i f i c a n t l y (P<0.05). With an R( value of 0.28, the model f i t t e d to e x p l a i n the v a r i a t i o n due to t o t a l p r o t e i n was s i g n i f i c a n t at (P<0.05). P e r i o d three had the lowest l a c t o s e content, while p e r i o d four had the highest (Table 19). 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 between the milk l a c t o s e content i n p e r i o d two and the o t h e r s . M i l k l a c t o s e content i n c r e a s e d s i g n i f i c a n t l y (P<0.05) with heat t r e a t e d a l f a l f a r a t i o n s . .86 (Table 20). The model f i t t e d to e x p l a i n the above r e s u l t s had an R-squared value of 0.37 and was s i g n i f i c a n t at (P<0.05). .87 DISCUSSION Feed composition. The s l i g h t increase in NDF with heat treatment (Table 7), could possibly be associated with the f i b r e nitrogen (N). It i s possible that before the protein supplements were heated, most of the f i b r e N was associated with ADF (ligno-c e l l u l o s e ) . After heating, the additional f i b r e N was associated with hemicellulose. Knipfel et a l • (1983) observed a similar r e l a t i o n s h i p when a l f a l f a meal was dry heated. Van Soest (1965) has also suggested that M a i l l a r d reactions might cause binding of the protein to i n d i g e s t i b l e carbohydrate fractions of the c e l l wall. Acid detergent insoluble nitrogen (ADIN) increased following heating. This further indicates that some association could have occurred on heating the protein supplements. The nutrients in the complete rations were similar (P<0.010) within the main treatments calculated on the basis on the feed consumed (Table 7). It i s possible that animals did very l i t t l e selection at feeding. Degradability of canol a and a l f a l f a c o n c e n t r a t e s . For both Canola and A l f a l f a concentrates (Table 10), the soluble fractions (a) and the degradation rate constants (c) decreased with heat treatment. In a l l cases the p o t e n t i a l l y degradable fractio n (b) of the DM increased with heating of the concentrate. Knipfel et a l . (1983) observed an increase in the hemicellulose components of NDF when a l f a l f a was . .88 heated between 480 and 1440 minutes. He also noted a s l i g h t decrease in the t o t a l nitrogen with the same temperatures. With heating of canola concentrate, both soluble CP f r a c t i o n (a) and the p o t e n t i a l l y degradable CP f r a c t i o n (b) decreased. It i s possible that M a i l l a r d reactions may have caused the protein to bind on to i n d i g e s t i b l e carbohydrates in the c e l l w a l l . The p o t e n t i a l l y degradable CP f r a c t i o n (b) could also have been reduced through the formation of several crosslinkages or through interactions with other plant components. The fact that ADIN content increased by 12.7% (Table 7) between ordinary and heated canola concentrates shows the p o s s i b i l i t y of protein heat damage to have been quite high. Although the soluble CP fr a c t i o n (a) decreased with the heating of a l f a l f a concentrates, the p o t e n t i a l l y degradable f r a c t i o n (b) for both DM and CP, increased with heat treatment. The increase in the p o t e n t i a l l y degradable f r a c t i o n (b) for the DM could be at t r i b u t e d to some degree of protein heat damage. However, the increase in the "b" f r a c t i o n of CP i s the product of s t r u c t u r a l transformation of the protein (denaturation). The increase in ADIN content was 6.6% (Table 7) as compared to 12.7% for canola above. This shows that heat treatment for a l f a l f a concentrates possibly protected i t s protein and did not a f f e c t the amino acids d i g e s t i b i l i t y and a v a i l a b i l i t y as adversely as i t did with canola concentrates. A more p o s i t i v e response would therefore . .89 be expected on feeding heated a l f a l f a , than the unheated a l f a l f a concentrates. Canola based r a t i o n s . Although the animals gained weight throughout the experiment, the rate of gain declined with the la c t a t i o n period. As a result of reduced energy and protein demands, due to the dropping milk y i e l d , voluntary feed intake would be expected to decrease. The s l i g h t increase in period three d i g e s t i b i l i t y values could be due to variations in the heat treatment of the canola concentrate. A reduction in the amount of heat applied would be expected to result in increased CP d i g e s t i b i l i t y . The increased DM and CP d i g e s t i b i l i t y with long chop hay rations (Table 12), could be attributed to a reduced passage rate, increased rumen retention time and hence enhanced rumination and reduced intake. Increased hay p a r t i c l e size would resu l t in the increase of the time a v a i l a b l e for microbial attachment to the digesta, and thus increase rumen fermentation. Work by Kerley et a l . (1985), Pearce and Moir (1964) and also Welch, (1986) has shown the e f f e c t s of rumen residence and passage rate on d i g e s t i b i l i t y . Welch also observed that p l a s t i c ribbons, 7-cm long required extensive rumination and p a r t i c l e size reduction before they could pass from the rumen. The decrease in NDF d i g e s t i b i l i t y with short chop hay was contrary to what was expected in view of the increased . .90 surface area. It i s however possible that with the short chop hay, an increase in the rate of the digesta passage rate e f f e c t on NDF d i g e s t i b i l i t y was greater than the increased surface area e f f e c t . Comparing the ordinary to heated canola treatments, a reduction in NDF d i g e s t i b i l i t y could be caused by heating i.e the result of protein association with the hemicellulose f r a c t i o n (Knipfel et a l . , 1983; Van Soest, 1982). This might res u l t in M a i l l a r d reactions, thus causing binding of the protein to i n d i g e s t i b l e carbohydrate fractions of the c e l l wall. The similar DM and CP d i g e s t i b i l i t y between the long chop rations (Table 1 2 ) , could possibly represent the effects an altered fermentation s i t e v i z : With the heated rations at t r i b u t e d to lower tr a c t fermentation, reduced d i g e s t i b i l i t y would not be expected for CP, but with ADF and NDF. NDF d i g e s t i b i l i t y declined s i g n i f i c a n t l y with heat treatment. A similar case could be made for the short chop hay rations, although heat treated rations may have encountered increased passage and increased rumen bypass. DM d i g e s t i b i l i t y declined when heated canola concentrate was fed together with the short hay. Intake is negatively related to the dietary NDF content (Van Soest et a l . , 1984). Hence, increased NDF d i g e s t i b i l i t y would be associated with increased voluntary intake. Table 12 shows that the unheated rations had a higher NDF d i g e s t i b i l i t y than the heated rations. Table 13 shows the . . 9 1 voluntary feed intake of the heat treated rations was s i g n i f i c a n t l y lower than the unheated rations. This was possibly caused by the i n d i g e s t i b l e M a i l l a r d products formed on heat treatment with the hemicellulose f r a c t i o n of NDF and protein. It i s also noted that the heated rations had a higher NDF content (Table 7). As a result of decline in the t o t a l milk production over the experimental duration (Table 14), t o t a l milk protein and t o t a l milk lactose declined s i g n i f i c a n t l y . Evidence to t h i s i s provided by the fact that both milk protein and lactose contents did not change s i g n i f i c a n t l y over the same period. The t o t a l values represent a product of the content and the t o t a l y i e l d . Milk fat content increased over the same period but at an i n s i g n i f i c a n t l e v e l . The s i g n i f i c a n t l y higher l e v e l s of milk fat and milk protein r e a l i s e d with unheated canola rations (Table 15), could be a r e f l e c t i o n of the increased a v a i l a b i l i t y of amino acids and energy for milk synthesis. Although protein and energy are interdependent, increasing energy supply has a greater e f f e c t on milk y i e l d than increasing protein (Broster and Oldham, 1981). The lower lev e l s of milk protein, fat and lactose observed with heated canola rations may possibly be at t r i b u t a b l e to a reduced palatabi1ity, reduced rumen CP degradability (due to heat damage), and hence reduced energy and protein supply. In practice^ i t is energy supply rather than protein supply which influence milk protein content . .92 ( B r o s t e r and Oldham, 1981). Energy w i l l however become l i m i t i n g i f l e s s d i g e s t i b l e feeds and forages are used (Van Soest et a l . , 1984). Although the r a t i o n s were formulated to p r o v i d e the animals s u f f i c i e n t ME, i t i s p o s s i b l e that a f t e r h e a t i n g canola meal, the ME l e v e l was reduced because of a lower CP d i g e s t i b i l i t y . Hay p a r t i c l e s i z e had i n s i g n i f i c a n t e f f e c t on milk y i e l d and i t s composition (Table 15). P o s s i b l y t h i s i s r e l a t e d to the v o l a t i l e f a t t y a c i d s p r o p o r t i o n s i n the rumen. A higher a c e t a t e r p r o p i o n a t e r a t i o i n the rumen would promote higher milk f a t . I t i s p o s s i b l e t h a t t h i s r a t i o remained r e l a t i v e l y c o n s t a n t with the two hay s i z e s c o n s i d e r e d . A l f a l f a based r a t i o n s . Throughout the experiment d i g e s t i b i l i t y of any n u t r i t i o n a l component would have been expected to remain c o n s t a n t , i f r a t i o n s were maintained uniform i n terms of heat treatment and chemical c o m p o s i t i o n . T h i s was observed (Table 16) except f o r DM and CP d i g e s t i b i l i t y i n p e r i o d t h r e e . P e r i o d three a l s o marks the removal of f i v e animals i n t h e i r l a t e r p a r t of l a c t a t i o n . In view of t h e i r low milk p r o d u c t i o n , i t i s p o s s i b l e t h a t the animals dropped were g a i n i n g more weight than the average cow i n the herd, and had a h i g h e r d i g e s t i b i l i t y . T h e i r removal would r e s u l t i n i n c r e a s e d feed i n t a k e , reduced d i g e s t i b i l i t y and the average l i v e w e i g h t gain would drop due to higher p r o d u c t i o n . A drop i n average l i v e w e i g h t gain was observed i n the p e r i o d that . .93 followed. Heat treatment of a l f a l f a concentrate may not have e f f e c t i v e l y reduced the CP degradability in period three due to non uniformity in the heating or in the mixing of the rations. This would explain the increased DM and CP d i g e s t i b i l i t y observed over t h i s period. Since ADF content of the diet did not change s i g n i f i c a n t l y over the experimental period, the lower than expected d i g e s t i b i l i t y c o e f f i c i e n t in period two i s mainly a t t r i b u t a b l e to random error perhaps also due to f i l t r a t i o n problems, contamination or poor marker recovery. High concentrate rations fed to cows resu l t in rapid rumen fermentation, and hence a low rumen pH (Orskov, 1982). Ce l l u l a s e a c t i v i t y would then be reduced (Van Soest, 1982), and therefore less of the fibrous hay material would be degraded in the rumen. The smaller hay p a r t i c l e s would require less rumination (Kerley et a l . , 1985; Pearce and Moir, 1964) and degradation would proceed to a greater extent than with a long p a r t i c l e s i z e hay. Further digestion in the lower t r a c t would result in higher CP and NDF fermentation. This i s possibly what resulted in the higher d i g e s t i b i l i t y of short hay rations indicated in Table 18 as compared to the other rations. The results also showed that hay p a r t i c l e size did not contribute s i g n i f i c a n t l y to DM and ADF d i g e s t i b i l i t y for the unheated rations. It i s therefore also possible that due to r e l a t i v e s i m i l a r i t y in hay p a r t i c l e s i z e , passage rate was not enhanced s i g n i f i c a n t l y by the short hay p a r t i c l e ..94 s i z e . If passage rate remained r e l a t i v e l y constant for both p a r t i c l e sizes, then rumen degradability would be higher with the short hay size than with the longer hay p a r t i c l e s due to the greater surface area of the former. As a result of heat treatment of the a l f a l f a rations, a high extent of rumen bypass would be expected. With the concentrate portion of the ration bypassing the rumen, the pH in the rumen would not drop markedly. Hence rumen pH may possibly have remained r e l a t i v e l y conducive to c e l l u l a s e a c t i v i t y . Short hay p a r t i c l e s would have greater surface area accessible to microbial attack, and therefore increased digestion. Kerley et a l . (1985) however observed a higher passage rate with reduced hay p a r t i c l e s i z e . Rumen digestion i s the net result of digestion and passage rate. Increasing passage rate decreases the time available for microbial attachment to the digesta, thus decreasing rumen fermentation. E s s e n t i a l l y t h i s would resu l t in the heated a l f a l f a + short chop hay r e a l i z i n g less nutrients (DM, CP, ADF and NDF) d i g e s t i b i l i t y than the unheated a l f a l f a + long chop hay. Results obtained (Table 17) show that t h i s was the case. ADF d i g e s t i b i l i t y did not however show a s i g n i f i c a n t response with changes in the hay p a r t i c l e length. Heated a l f a l f a concentrate + long chop hay rations were more d i g e s t i b l e (DM, CP and NDF) than the unheated a l f a l f a concentrate + long chop hay (Table 1 8 ) . This i s possibly a t t r i b u t a b l e to an improved synchrony in the release of . .95 nitrogen in the rumen with heated a l f a l f a rations since both the rate of DM and CP degradability in the rumen were reduced on heating (Table 9). The lower d i g e s t i b i l i t y c o e f f i c i e n t s observed with heated a l f a l f a rations + short chop hay compared with rations having similar but unheated ingredients could be the result of reduced microbial degradation, reduced retention time and hence reduced DM and CP degradability and high passage rate. This is in view of the fact that both rations had short chop hay, and hence p a r t i c l e size remained constant. Reduced p a r t i c l e size enhances passage rate, thus reducing the extent of digestion (Kerley et a l . , 1985). This was r e f l e c t e d in the nutrient d i g e s t i b i l i t i e s shown in Table 17 and 18. Table 19 shows the s i g n i f i c a n t changes occurring in milk composition throughout the experiment. As l a c t a t i o n progressed the t o t a l milk production also declined. Since milk fat content did not change s i g n i f i c a n t l y , only the t o t a l fat would decrease with l a c t a t i o n period. Total milk fat was calculated as the product of milk fat content and t o t a l milk y i e l d . Lactose content changed s l i g h t l y . Changes in the lactose content could r e f l e c t the changes in osmotic value due to other solids and minerals in late l a c t a t i o n . Heated a l f a l f a rations resulted in s i g n i f i c a n t l y higher l e v e l s of milk production, t o t a l milk f a t , t o t a l protein and a higher milk lactose content (Table 20). Milk fat and protein contents did not change s i g n i f i c a n t l y . Hence the . .96 i n c r e a s e i n milk y i e l d c o n t r i b u t e d to the i n c r e a s e d t o t a l f a t and t o t a l p r o t e i n . The i n c r e a s e i n milk y i e l d c o u l d be due to the f a c t that n u t r i e n t s r e s u l t i n g from the h i g h l y d i g e s t i b l e heated r a t i o n s were e f f i c i e n t l y u t i l i z e d i n m i l k p r o d u c t i o n and l i v e w e i g h t g a i n . Increased milk y i e l d and milk f a t (P<0.10) with i n c r e a s e d a v a i l a b i l i t y of both amino a c i d s and energy has been observed i n other t r i a l s (Orskov 1981; F i s h e r 1972). With i n c r e a s e d amino a c i d s a v a i l a b l e f o r g l u c o g e n e s i s , i n c r e a s e d f a t and l a c t o s e content c o u l d have been r e a l i z e d . From Table 10, h e a t i n g a l f a l f a c o n c e n t r a t e s a l s o provided some p r o t e c t i o n of the p r o t e i n from rumen m i c r o b i a l d e g r a d a t i o n . Long chop hay r e s u l t e d i n i n c r e a s e d f a t content (P<0.10) and hence t o t a l milk f a t (Table 20). T h i s has been observed i n other t r i a l s ( B r o s t e r et a l . , 1981; Orskov 1982) and has been a s s o c i a t e d with the rumen v o l a t i l e f a t t y a c i d s p r o p o r t i o n s . A c l o s e r e l a t i o n s h i p between m i l k f a t content and the a c e t a t e : p r o p i o n a t e r a t i o was observed, e s p e c i a l l y when the r a t i o f e l l below 3:1 ( B r o s t e r e t a l . , 1981). .97 SUMMARY AND CONCLUSIONS In t h i s t r i a l we set out two objectives as indicated in the opening section. From the results obtained, the objectives were achieved. However due to interaction between the treatment of the concentrate and the hay p a r t i c l e s i z e , some e f f e c t s could not be established separately. It was also established that the two hay chop lengths had similar e f f e c t s in most of the att r i b u t e s under investigation. Canola based rations. The degradability of canola meal concentrate was reduced by heat treatment. This did not r e f l e c t a s i g n i f i c a n t heat damage of canola protein, since CP d i g e s t i b i l i t y of the heated rations was sim i l a r to the unheated rations. Heat treatment did not affe c t DM, CP and ADF d i g e s t i b i l i t y s i g n i f i c a n t l y . NDF d i g e s t i b i l i t y decreased with heat treatment. Heat treatment also d r a s t i c a l l y reduced the voluntary feed intake. Although heat treatment had no s i g n i f i c a n t e f f e c t on the t o t a l milk y i e l d ; butter fat and milk protein contents decreased with heat treatments. Milk lactose remained r e l a t i v e l y constant. Forage p a r t i c l e length had i t s greatest e f f e c t when fed together with the heat treated rations. Overall reduced . .98 forage p a r t i c l e s i z e r e s u l t e d i n lower but i n s i g n i f i c a n t DM, CP, ADF and NDF d i g e s t i b i l i t y . With heat treatment s i m i l a r but s i g n i f i c a n t r e d u c t i o n was observed except f o r NDF. V o l u n t a r y feed intake was not s i g n i f i c a n t l y i n c r e a s e d with reduced forage p a r t i c l e s i z e . Except f o r t o t a l milk l a c t o s e content, t h e r e was no s i g n i f i c a n t change i n the other milk components with d i f f e r e n t forage p a r t i c l e s i z e . A l f a l f a based c o n c e n t r a t e s . Heat treatment r e s u l t e d i n reduced DM and CP d e g r a d a b i l i t y . T h i s c o u l d r e f l e c t s i g n i f i c a n t p r o t e i n d e n a t u r a t i o n s i n c e CP and ADF d i g e s t i b i l i t y of heated r a t i o n s was s i g n i f i c a n t l y lower than the unheated r a t i o n s . The e f f e c t of heat treatment was p a r t i c u l a r l y n o t able with s h o r t p a r t i c l e s i z e hay. With r a t i o n s based on short chop hay, both DM and CP d i g e s t i b i l i t y were reduced. NDF d i g e s t i b i l i t y decreased most n o t a b l y with s h o r t hay r a t i o n s . Heat treatment of the r a t i o n s r e s u l t e d i n reduced v o l u n t a r y feed i n t a k e . Heat treatment r e s u l t e d i n i n c r e a s e d milk y i e l d , milk f a t , p r o t e i n and l a c t o s e c o n t e n t . Hay p a r t i c l e s i z e d i d not a f f e c t v o l u n t a r y feed i n t a k e s i g n i f i c a n t l y . T o t a l milk f a t i n c r e a s e d w i t h long chop hay. However, the other milk components, i n c l u d i n g milk y i e l d d i d not change s i g n i f i c a n t l y with changes i n forage p a r t i c l e s i z e . . .99 GENERAL SUMMARY The f i r s t study was undertaken with two major o b j e c t i v e s as o u t l i n e d i n the opening s e c t i o n . Tables 3 , 4 , 5 and 6 show the r a t e and extent of rumen degradation of the f e e d s t u f f s s t u d i e d . The r e s u l t s o b t a i n e d were based on v a r i o u s d i g e s t a flow r a t e s . T h i s extends t h e i r a p p l i c a t i o n to d i f f e r e n t f e e d i n g regimes. Suggestions on the p o s s i b l e combinations of the f e e d s t u f f s i n the d a i r y cow r a t i o n were made i n the c o n c l u d i n g remarks. With the feed samples at hand t h e r e f o r e , both o b j e c t i v e s were adequately met. In Kenya, seasons have a major i n f l u e n c e on feed a v a i l a b i l i t y , and hence, on the d a i r y cows plane of n u t r i t i o n . E f f i c i e n t u t i l i z a t i o n of forages over the c r i t i c a l p h y s i o l o g i c a l p e r i o d s of the d a i r y cow would i n v o l v e c o n s i d e r a t i o n s on the forage production p o t e n t i a l , and a l s o the optimum time to h a r v e s t f o r c o n s e r v a t i o n . Information on the f e e d i n g value of f o r a g e s at d i f f e r e n t stages of development i s t h e r e f o r e of v i t a l importance. Feed samples e v a l u a t e d i n t h i s study were obtained two months a f t e r the end of the r a i n y season. T h i s marks the time when most forages were at peak q u a l i t y . The r e s u l t s o b t a i n e d and hence, the recommendations that were made r e f l e c t the use of the f e e d s t u f f s at t h e i r peak q u a l i t y . D e g r a d a b i l i t y v a l u e s o b t a i n e d i n t h i s t r i a l are t h e r e f o r e at best u s e f u l as a . . 1 0 0 stardard in the evaluation of conserved feed materials. It would also be useful to carry out similar investigations with forages sampled over the dry season. This would provide an estimate of the decline in degradability with maturity and such aspects as dessication. Through comparisons at various phy s i o l o g i c a l stages and over the seasons, feed conservation needs and the type of supplementation required would be further i d e n t i f i e d . Laksesvela and Said (1978) established the c r i t i c a l need for correct energy and protein supplementation of Kenyan forages when used for milk production. The rapid increase in protein requirement which arises with l a c t a t i o n has been shown not to be adequately met by microbial protein supplies alone. Feeding highly degradable proteins would supply i n s u f f i c i e n t amounts of amino acids to the inte s t i n e s over the l a c t a t i o n period. As the Kenyan milk production i n t e n s i f i e s , a greater need w i l l be r e a l i s e d for use of rumen undegradable proteins. Canola meal i s used as a protein supplement for livestock in Canada. Canola i s a genetic c u l t i v a r of rapeseed. The production of rape (Brassica napus) gave excellent r e s u l t s in Kenya (Kidner, 1981). On the other hand, a l f a l f a i s an established protein supplement both in Kenya and in Canada. Both canola and a l f a l f a have a balanced amino acid p r o f i l e conducive to milk production. Heat treatment of these supplements or any forage e.g desmodium, would be aimed . . 101 at allowing s i g n i f i c a n t amounts of the dietary protein to bypass ruminal degradation. Thus, the e f f i c i e n c y of u t i l i z a t i o n by the animal would be improved. 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Wilson, J.R. and D.J. Minson. 1983. Influence of temperature on the d i g e s t i b i l i t y of t r o p i c a l legume Macropt ilium  atropurpureum. Grass and forage science 38:39. Wohlt, J.E., C.J. Sniffen and W.H. Hoover. 1973. Measurement of protein s o l u b i l i t y in common feedstuffs. J . Dairy S c i . 56:1052. Zinn, R.A., L.S. B u l l and R.W. Hemken. 1981. Degradation of supplemental proteins in the rumen. J. Anim. S c i . 52:857. ..111 APPENDICES. Appendix 1: Composition of the d a i r y r a t i o n s formulated. Canola based r a t i o n Components: 100 kgs. mix Coarse ground b a r l e y 84.946 Canola meal 10.153 Molasses 1 .667 Limestone 1 .583 Premix 0.833 S a l t 0.416 D i c a l c i u m phosphate 0.400 A l f a l f a based r a t i o n Components: 100 Kgs. mix A l f a l f a 49.182 Ba r l e y 46.688 Molasses 1 .667 Limestone 0.143 Premix 0.833 S a l t 0.416 D i c a l c i u m phosphate 1 .070 The composition of the Premix was; Components: N u t r i e n t s per Kg of Premix V i t a m i n A 1,600,000 IU Vit a m i n D 320,000 IU Vi t a m i n E 4,000 IU Selenium 40 mg Iodine 0.3 g Cobalt 0.1 g Copper 5 g Zinc 20 g Manganese 16 g I ron 16 g ..112 Appendix 2. Experimental layout used in the t r i a l . Canola based Treatment 1 - SH + Unheated canola based cone (OC) Treatment 2 - SH + Heated canola based cone (HC) Treatment 3 - LH + OC Treatment 4 - LH + HC A l f a l f a based Treatment 1 - SH + Unheated a l f a l f a based cone (OA) Treatment 2 - SH + Heated a l f a l f a based cone (HA) Treatment 3 - LH + OA Treatment 4 - LH + HA .113 

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