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Evaluation of the parameters influencing the weight of beef cows Hiley, Peter Graham 1976

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An Evaluation Of The Parameters Influencing The Height Of Eeef Cows By PETER GRAHAM HILEY B.Sc., University of Reading, G.B. 1970. M.Sc, University of Nairobi, Kenya. 1973. A thesis submitted in p a r t i a l fulfilment of the requirements for the degree of Doctor of Philosophy in THE FACOLTY OF GRADUATE STUDIES (Department of Anircal Science) we accept t h i s thesis as conforming to the reguired standard UNIVERSITY OF BRITISH COLUMBIA November, 1976. (e) Peter Graham Hiley, November, 1976 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the regu i rement s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I a g ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d tha t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i thout my w r i t t e n p e r m i s s i o n . f\r\\ A J  Department o f P ( \ (A^ V 3 C ( ^ v c ^ The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date // / *C Abstract The body weight of beef cows (cow weights) on nine ranches and farms located in the province of B r i t i s h Columbia were recorded each f a l l and spring for three years. Cow weights were also recorded on two additional occasions during the winter i n the largest of these herds. The cows in these herds were a l l straightbred Hereford or Angus cows, or crossbreds of one or other of these breeds. During the summer fi v e of the herds used rangeland, and four used pasture. Each herd calved in the spring aft e r overwintering on conserved forage. The influence of breedtype, year, age, season and herd on the spring and f a l l weight records were determined by a l e a s t -squares analysis as outlined by Harvey (1 975). Season was found to have a major influence on cow weight. Each weight change (considered as a percentage of the mean weight during the period) was included as a dependent variable in separate analyses. In addition to the parameters already mentioned, c a l f sex, c a l f age, ca l f weaning weight, previous weight change and the i n t e r v a l from calving to weighing i n the spring were included where appropriate i n the models for these analyses. The two mid-winter weights were included i n a sim i l a r s t a t i s t i c a l analysis to determine the influence of pregnancy £er se on cow weight in t h i s herd. The parameters f i t t e d in t h i s model were age, year, age x year, days pregnant (DP), DP2 and DP3. Age, season and herd were found to be s i g n i f i c a n t sources i i i o f v a r i a t i o n i n the cow weight r e c o r d s ; bat, w i t h i n each herd, g e n e t i c a l l y d i f f e r e n t breedtypes normally had s i m i l a r weights. The cows on summer ran g s l a n d were on average 119.0 l b . l i g h t e r than those on summer pasture. The i n c r e a s e i n weight over age and the seasonal f l u c t u a t i o n s around t h i s mean growth curve a l s o v a r i e d s i g n i f i c a n t l y between herds. However, i n a l l but one of the herds there was a weight l o s s each winter and a weight gain each summer. The mean s p r i n g / f a l l weight d i f f e r e n c e was 114.2 l b . The mean mature age of the cows was s i x , and the mean mature weight was 1033.9 l b . The summer change i n weight of a cow depended on age and herd, but not on breedtype. Younger cows gained more weight through the summer than o l d e r cows; the i n f l u e n c e of herd on cow weight was not c o r r e l a t e d with any s i n g l e f a c t o r . Summer weight change was not i n f l u e n c e d by the c a l f the cow suckled d u r i n g the summer, but cows which l o s t the most weight during the previous winter gained the most the f o l l o w i n g summer. The winter weight change of a cow was not the same f o r a l l ages and breedtypes, but d i f f e r e d from herd to herd a c c o r d i n g t o the l e v e l of winter f e e d i n g i n each herd. Again t h e r e was a c l o s e c o r r e l a t i o n between t h i s weight change and that i n the previous p e r i o d . The winter weight l o s s was found to continue through the i n t e r v a l from c a l v i n g t o weighing. The average weight l o s s d u r i n g t h i s p e r i o d was around 0.7 l b . per day. A mean weight i n c r e a s e of 101.4 l b . was recorded between the 90th and 260th days of pregnancy. There was then a 6.8 l b . weight l o s s i n the remaining 25 days through t o p a r t u r i t i o n . The weight l o s s at p a r t u r i t i o n was 80.0 l b . or 7.3% of the cow's p r e - p a r t u m w e i g h t . V Table 2.1 Contents Chapter T i t l e Pacje Abstract i i L i s t of Tables v i i L i s t of Figures v i i i Acknowledgements ix 1 Introduction 1 2 Literature Review Absolute body weight 3 Seasonal change i n weight ......10 3 Materials and Methods The method of data c o l l e c t i o n .....16 The farms and ranches included in t h i s research .....20 4 S t a t i s t i c a l Analysis The dependent variables 25 The potential independent variables .....26 The type of model 34 The method of analysis ..36 The model for each analysis 39 5 Results Spring and f a l l weight analysis .........43 Summer change i n weight analysis-1 ...... 59 Summer change in weight analysis-2 ...... 65 Winter change i n weight analysis ........ 66 Winter analysis for herd 2 ..............76 6 Discussion Section 1 - Discussion of the Analyses Weight analysis 84 Summer change in weight - Analysis 1 ....91 Summer change i n weight - Analysis 2 ....94 Winter change in weight 96 Herd 1 weight changes , 99 Winter analysis i n herd 2 ......101 Section 2 - The Influence of the Parameters Breedtype 103 v i Herd 104 Age .105 Year ............107 Season 107 Spring i n t e r v a l ............114 Calf age, c a l f sex and c a l f weaning weight ...........114 Pregnancy and pa r t u r i t i o n ..............116 Section 3 - Conclusions ..........117 Bibliography .......123 Appendix 1 Least sguare constants ..128 Appendix 2 Weighing dates for each herd ...........138 v i i LiSi 2f Tables Table T i t l e £ac[e 1 Some parameters influencing the weight of a beef cow ................. 6 2 Some parameters influencing the weight change of a beef cow .................. 11 3 Analysis of variance of spring and f a l l absolute weights .........45 4 l e a s t square estimates for absolute spring and f a l l weights ....46 5 Seasonal weight changes i n each age subclass . ............52 6 Seasonal weight changes i n each year .........52 7 Winter weight change i n each herd 56 8 Analysis of variance for summer change i n weight for two years ............... 61 9 Least square estimates for summer change i n weight for two years 62 10 Analysis of variance for summer change i n weight in 19 74 .....67 11 Least sguare estimates for summer change i n weight i n 1974 ................. 68 12 Analysis of variance for winter change i n weight ..72 13 Least sguare estimates for winter change in weight ................. 73 14 Analysis of variance for winter weights when considered as days pregnant at weighing ................. 80 15 Least sguare estimates for winter weights when considered as days pregnant at weighing ............81 v i i i L i s t of Figures Figure T i t l e £age 1 The weight of the cows i n each herd .......... 48 2 The increase in weight over age .........50 3 The seasonal fluctuations in weight around the mean growth curve ................. 53 4 The spring and f a l l weights i n each herd .....55 5 The growth curve in each herd ................ 58 6 The summer change in weight in each age subclass 64 7 The summer weight change i n each herd 70 8 The winter weight change i n each age subclass .....75 9 The winter weight change i n each herd/age subclass 77 10 The winter weight change i n each herd/year subclass ...78 11 The changes in weight during pregnancy and p a r t u r i t i o n i n herd 2 .........82 i x In c a r r y i n g out t h i s r esearch I have r e c i e v e d a s s i s t a n c e and guidance from many people. I would l i k e to extend a c o l l e c t i v e word of thanks to a l l of them. I would e s p e c i a l l y l i k e to mention my s u p e r v i s o r , Dr. John Hodges. His encouragement, i n t e r e s t and patience helped me through the t r i a l s and t r i b u l a t i o n s which are i n e v i t a b l e i n t h i s type of research. I am g r a t e f u l f o r h i s guidance and t h a t of my a d v i s o r y committee, Dr. V.C. B r i n k , Dr. D.H. C h i t t y , Dr. E.G. Peterson, Dr. R.J. Hudson and Dean SJ.D. K i t t s . T h eir i n p u t was an important f a c t o r i n the progress of t h i s research. The study i t s e l f would not have been p o s s i b l e without the funding s u p p l i e d by the B r i t i s h Columbia Department of A g r i c u l t u r e and the B r i t i s h Columbia A r t i f i c i a l Insemination Centre. I am most g r a t e f u l t o these o r g a n i s a t i o n s f o r t h e i r i n t e r e s t and g e n e r o s i t y with r e s p e c t to t h i s r e s e a r c h . I would a l s o l i k e t o thank the B r i t i s h Columbia Beef C a t t l e Grower's A s s o c i a t i o n f o r the B r i g a d i e r Bostock Memorial Research Grant which they awarded to me during the course of the r e s e a r c h . The c o - o p e r a t i n g beef producers were an e s s e n t i a l component of t h i s r e s e a r c h . I am indebted to these i n d i v i d u a l s f o r the i n t e r e s t they showed i n the study and the time and e f f o r t they put i n t o completing i t . L a s t l y , I would l i k e to thank Pippa Gibbs f o r her help i n c o m p i l i n g and proof reading t h i s t h e s i s and Peter Leggat f o r h i s d i l i g e n c e i n making the i n i t i a l c o n t a c t s with the c o - o p e r a t o r s i n the f i e l d . 1 CHAPTER J Introduction Genetic differences between and within breeds i n the rate and e f f i c i e n c y of gain are related to differences between animals i n their mature body weight (Klosterman, 1972; Brown, 1970) and rate of maturing (Fitzhugh and Taylor, 1971), In the beef industry such differences are exploited through the male side of a breeding program, A b u l l which has a high breeding value for growth w i l l tend to have a r e l a t i v e l y heavy mature weight. His female offspring which enter a breeding herd w i l l , owing to the high h e r i t a b i l i t y of mature body weight (Brinks et a l . , 1964; Bennyshek and Marlowe, 1973; Francois et a l . , 1973), also tend to be r e l a t i v e l y heavy. Previous research indicates that the nutrient reguirement of a beef cow i s related to her weight. As f i f t y to sixty percent of the t o t a l feed energy reguired to raise a beef animal from conception to slaughter i s used by i t s dam for maintenance and production (Klosterman, 1972; Thiessen, 1976), the extra cost of keeping heavier cows i s l i k e l y to be s i g n i f i c a n t . In B r i t i s h Columbia the beef industry i s based on a cow-calf system; in t h i s type of production system the proportion consumed by the dam £er se i s considerably higher, and the extra cost i s correspondingly greater. This increased feed cost w i l l , however, be o f f s e t i n part by the f a s t e r growth which a genetically heavier cow w i l l pass on to i t s c a l f , together with a maternal environmental advantage in utero. 2 Weight, however, i s a dynamic rather than a s t a t i c t r a i t . Consequently, a c l a s s i f i c a t i o n of the productivity of a cow simply i n terms of a single weight can be misleading (Bowman, 1972). In slaughter animals considerable information i s available on the environmental parameters which influence the phenotypic expression of an animal's genetic a b i l i t y to grow i n early l i f e . However, the i r influence through maturity in a breeding female i s not well documented. The objective of this research was thus to r e c t i f y t h i s deficiency by evaluating the parameters influencing the growth, up to and beyond maturity, of beef cows on cert a i n farms and ranches i n the southern half of the province of B r i t i s h Columbia. The c r i t e r i a which have been used to define mature weight i n previous studies are not i d e n t i c a l . In t h i s study mature body weight i s defined as the weight of an animal to which no further s i g n i f i c a n t annual increments are added. This i s eguivalent to the d e f i n i t i o n of mature weight used by Brinks et a l . (1962), Fitzhugh (1965) and Fitzhugh and Taylor (1971). It i s si m i l a r to the asymptote of a f i t t e d growth curve which was the c r i t e r i o n used to define mature weight by Joandet and Cartwright (196 9), 3 CHAPTER 2 Review Of Literature Mature ' s i z e 1 i s a phenotypic and genetic c h a r a c t e r i s t i c generally attributable to a breed of beef c a t t l e (Mason, 1971; Adams, Garret and Elings, 1973). The 'size* of a cow has been variously described by a single measurement or by an index of several (Jeffrey and Bsrg, 1972; Biaglo and Meragalli, 1972; O'Mary, Brown, and Ensminger, 1972; Tanner, Cooper and Kruse, 1956; Simpson et a l . , 1972, Brown et a l . , 1956 a S b ). Variation in the l e v e l of n u t r i t i o n has l e s s effect on s k e l e t a l measurements than on body weights, e s p e c i a l l y as a cow approaches maturity. Conseguently the former i s a more stable estimate of cow s i z e (Brown et a l . , 1956 a & b ). Skeletal measurements, however, are affected by stance, and also reguire precise location of anatomical points for accurate measurement. Consequently, Taylor (1963) reports a ten-fold change from t r i a l to t r i a l i n the accuracy of body measurements of monozygous twins, and Johansson and Hildman (1954) report that the error incurred in taking body measurements i s almost three times greater than that incurred in weighing. Other workers, Brookes and Harrington (1961) and Fisher (1975), also mention t h i s problem of poor r e p e a t a b i l i t y , especially in beef c a t t l e , which tend to be more d i f f i c u l t to handle than dairy c a t t l e . Mean mature weight of females of beef breeds i s reported to vary from 750 l b . in Dexters (Thiessen, 1976) to 2240 l b . i n Maine-Anjou (Mason, 1973). Most research studies on the body 4 weight of beef cows have included Hereford c a t t l e . Within t h i s breed mature weight i s reported to vary from 997 l b . (Kogerand Knox, 1951} to 1280 l b . (Guilbert and Gregory, 1952), with many intermediate values (Vacarro and D i l l a r d , 1966; Clark et a l . , 1958; Brinks et a l . , 1962; Urick et a l . , 1971; Joandet and Cartwright, 1969; Fitzhugh, 1965; Fitzhugh, Cartwright and Temple, 1967; Edwards and Bailey, 1975; Brown, Brown and Butts, 1972). Reports vary on the age at which Hereford cows reach mature weight. Bennyshek and Marlowe (1973) and Guil.bert and Gregory (1952) found that i t occurred at f i v e years of age; others report that cows could be twice t h i s age before reaching t h e i r mature weight (Orick et a l . , 1971; Fitzhugh, 1965; Fitzhugh et a l . , 1967; Clark et a l . , 1958; Kilkenny and S t o l l a r d , 1973; Joandet and Cartwright, 1969). The body weight of Hereford cows has also been found to decline after eight (Knox and Roger, 1945), nine (Clark et a l . , 1958; Brinks et a l . , 1962) and fourteen (Bennyshek and Marlowe, 1973) years of age. There are fewer reports on the age and weight at maturity of other breeds. Urick et a l . (1971) report that Angus and Charolais cows reach mature weights of 1160 lb. and 1290 l b . respectively at f i v e years of age. Brown et a l . (1956a) and Brown et a l . (1972) report a s i m i l a r age for Angus c a t t l e of 1065 l b . and 970 l b . mature weight respectively. However, Fitzhugh (1965) and Fitzhugh et a l , (1967) report that Angus cows reach mature weights from 840 l b . to 1135 lb. at around nine years of age. Brahman cows in this study were mature at between 840 lb. and 1135 l b . , and Santa Gertrudis between 950 l b . and 1120 l b . , at unreported ages. Crossbred cows 5 (seven-eighths Brahman:one-eighth Hereford) reached mature weights of 1080 l b . at four years of age i n a study by Joandet and Cartwright (1969) . These reports on age and weight at maturity indicate a variation between breeds and cows in their pattern of growth. This variation i s the result of environmental and genetic factors and t h e i r interactions. Table 1 l i s t s the most freguently reported of these. Herd The Herd Effect on the mean body weight of cows of the same breed in d i f f e r e n t herds reported by Fitzhugh (1965) and Fitzhugh et a l . (1967) was considerably greater than the Breed Eff e c t on the weight of cows in the same herd. These authors do not mention the grazing conditions for each herd. However, Edwards and Bailey (1975) report a difference between the mature weights of Hereford cows grazing summer range (1010 lb.) and those grazing e n t i r e l y on i r r i g a t e d pasture (1170 l b . ) . The herd differences reported by Fitzhugh . (1965) and Fitzhugh et a l . (1967) are presumably a product of such environmental differences, together with genetic differences between the herds, Such factors are inevitably included in the Herd Effect. Year The Year Effect was reported to be s i g n i f i c a n t by most of the authors l i s t e d i n Table 1. The environmental differences between years did not normally show any trend. Season The weight of a spring-calving cow i s normally l i g h t e r post-partum than i t i s in the f a l l at weaning (Fitzhugh, 1965; 6 Some Parameters Influencing the Weight of a Beef, Cow MLM BfiJJD HERD YEAR SEASON STATUS SIRE Bennyshek & Marlowe (1973) Anderson et a l (1973) Clark et a l (1958) Holloway S Totusek (1973) Joandet £ Cartwright (1969) Kilkenny S St o l l a r d (1973) Urick et a l (1971) s i g *** *** s i g s i g si g Fitzhugh et a l (1967) ** Brown et a l (1972) s i g Brown (1970) * •ig Fitzhugh (1965) ** ** *** sag ns ns ** sig s i g s i g s i g #•* * * ** l£teractigns Bennyshek & Marlowe (1973) Kilkenny & S t o l l a r d (1973) Urick et a l (1971) *** s i g ns year x age breed x herd age x breed year x age p<0.1 p<0.05 p.<0,005 le v e l of significance not given variable not s i g n i f i c a n t 7 Fitzhugh et a l . , 1967; Vacarro and D i l l a r d , 1966; Jeffrey and Berg, 1971) . However, Singh et a l . (1970) and Joandet and Cartwright (1969) report that cows lo s t weight during the period of l a c t a t i o n . When a cow i s weighed pre-partum i n the spring, Clark et a l . (1958) and Anderson et a l . (1973) report only a s l i g h t gain i n weight during t h i s summer period - 11 l b . and 9 l b . respectively. Brinks et a l . (1962) report that cows under f i v e years of age gain weight from pre-partum to weaning, while older cows lose weight. Ewing et a l . (1962) and Vacarro and D i l l a r d (1966) report that there i s i n i t i a l l y a l o s s i n weight after calving. The l a t t e r authors report a mean weight loss of 33 l b . during a sixty-day period after p a r t u r i t i o n . Ewing et a l . (1962) report that, prior to increasing i n weight with the spring grass, cows l o s t 17% of t h e i r weight the previous f a l l . Included i n this o v e r a l l loss was a 13% loss i n weight at p a r t u r i t i o n (119 l b . ) . They made no mention, however, of what proportion of the remaining H% was l o s t post-partum. Most workers report a loss i n weight through the winter. Naturally, when the cow i s weighed pre-partum the weight loss reported i s considerably smaller (Anderson et a l . , 1973) than that recorded for cows weighed post-partum (Jeffrey and Berg, 1971; Fitzhugh, 1965; Fitzhugh et a l . , 1967). However, Clark et a l . (1958) report a s l i g h t gain (7 lb.) from f a l l to spring (pre-partum) , whilst Brinks et a l . (1962) report Year E f f e c t s , i n d i c a t i n g both gains and losses during pregnancy from f a l l to spring (pre-partum), with the s l i g h t gain occurring more often. Pregnancy status This Seasonal Effect has been reported to d i f f e r between 8 cows suckling a c a l f and those which are dry. The l a t t e r have a s i g n i f i c a n t l y greater increase in weight through the summer and can be as much as 150 lb. heavier than the former i n the f a l l (Clark et a l . , 1958; Urick et a l . , 1971). Fitzhugh (1965) and Fitzhugh et a l . (1967) also report that a cow's weight i s influenced by whether she weaned or gave bi r t h to a c a l f in the previous year. Year of b i r t h Brown (1970) and Brown et a l . (1976) found that the year of bi r t h of a cow was a s i g n i f i c a n t factor i n influencing her weight. However, Brown (1970) mentions that the effect i s l i k e l y to be confounded with the influence of her s i r e i f he was used only i n a single year. Holloway and Totusek (1973) and Joandet and Cartwright (1969) did not f i n d t h i s Year of Birth Effect to be s i g n i f i c a n t . Acje at f i r s t calving Brown (1970) used f i v e non-linear models to describe the growth of Jersey and Hereford cows. Those parameters in the models f o r Jersey cows which reflected the rate of growth to maturity were s i g n i f i c a n t l y influenced by the age of the cow at f i r s t calving. I t did not aff e c t mature weight. Anderson (1973), Brown and Franks (1964) and Fitzhugh (1965) report that age at f i r s t calving s i g n i f i c a n t l y influenced the weight of three-year-old cows. Month of calving Fitzhugh (1965) and Fitzhugh et a l . (1967) report that cows calving at di f f e r e n t times of the year have d i f f e r e n t spring and f a l l weights. However, this Month of Calving Effect varied 9 across the ten herds in the study and was p a r t i a l l y confounded with a varying i n t e r v a l from p a r t u r i t i o n to weighing. Condition As expected, a cow's condition i s reported to have an e f f e c t on her weight (Bennyshek and Marlowe, 1973). For example, < Lowman (1975) showed that cows with a subjective condition score of one, weighed on average 150 l b . more than those with a condition score of f i v e . Meat and Livestock Commission (1975) and Barton (1967) discuss condition-scoring of c a t t l e and report a poor r e p e a t a b i l i t y between and within untrained observers. Brewis (1974) reports mean i n t r a - and inter-operator correlations i n condition-scoring of 0.83 (range 0.66 to 0.95) and 0 .70 (range 0.68 to 0.72) respectively. The f i v e operators i n t h i s study varied considerably i n th e i r experience. As Taylor (1963) mentions, i t i s to be expected, and has been confirmed i n t r i a l s , that measurements that are i n t r i n s i c a l l y most variable (such as those r e f l e c t i n g condition) invariably have the poorest r e p e a t a b i l i t y . Genotype Negative correlations have been reported between the degree of inbreeding of an animal and i t s growth i n early l i f e . (Dinkel, Bush and Minyard, 1968; Moore, Stonaker and Riddle, 1961; Alexander and Bogart, 1961). Anderson et a l . (1973) found a s i g n i f i c a n t e f f e c t of inbreeding on cow weight at breeding time, but not in the f a l l or pre-partum. Height at breeding time was recorded shortly a f t e r the cows had been t r a i l e d for three days, and the authors suggest that the i n a b i l i t y of the inbred cows to cope with t h i s stress resulted in t h e i r lower weights. 1 0 They also report a difference i n f a l l weight between the three selected l i n e s of cows i n their study. Fitzhugh (1965), Fitzhugh S i a l . (1967), Brown et a l . (1971) and Brown (1970) report a s i m i l a r Sire Effect., Studies of summer and winter changes i n weight as dependent variables are l i s t e d i n Table 2. The increase in weight and decrease i n weight respectively which normally occur during these periods were discussed above. A<je Vacarro and D i l l a r d (1966), Fitzhugh (1965) and Fitzhugh et a l . (1967) report that younger cows put on more weight through the summer than older cows. As mentioned previously, Brinks et a l . (1962) report that while older cows lose weight through the summer, younger cows gain weight. However, t h i s finding i s not i n c o n f l i c t with other work, since t h i s study used pre-partum spring weights. I f a correction were made for p a r t u r i t i o n weight loss a l l these cows would have been found to gain weight through the summer, with younger cows gaining more than older ones. Among the weight losses through the summer reported by Singh et a l . (1970) the younger cows l o s t more than the older ones. This anomalous result i s presumably a product of the a v a i l a b i l i t y of feed. when i t i s p l e n t i f u l younger cows can overcome the stress of l a c t a t i o n and express th e i r genetic reguirement to grow, when i t i s i n s u f f i c i e n t , l a c t a t i o n stress has a greater effect on the younger cows, causing them to lose more weight than t h e i r older contemporaries. However, age does not always influence weight change during t h i s suckling period (England et a l . , 1961). TABLE 2 Some Parameters Inf lugncing - the Weight Chang.e of- a Beef Cow MIMING M I HEED YEAR WEIGHT~ Vacarro 8 D i l l a r d (1966) s i g s i g * Carpenter et a l (1972) sxg Brinks et a l (1962) s i g sxg England et a l (1961) ns sxg s i g Fitzhugh et a l (1967) s i g s i g sig Fitzhugh (1965) s i g sig sig Singh et a l (1970) * * * =p<0.05 sig = l e v e l of significance not given ns = variable not s i g n i f i c a n t 12 Brinks et a l . (1962) report that when related to a pre-partum spring weight younger cows tend to increase in weight through the winter more than older cows. Fitzhugh (1965) and Fitzhugh et a l . (1967) report that when related to post-partum spring weight, winter weight loss i s greatest i n older cows. This age difference i s again linked to the younger cows' greater inherent reguirement to grow. Breed Reports of variation between breeds in weight changes during summer and winter periods are limited and inconsistent. Fitzhugh (1965) and Fitzhugh et a l . (1967) found that Angus averaged less weight gain or more weight loss through the summer than Herefords. Brinks et a l . (1962) found the opposite i n their study. Mean body, weight Mean body weight has been found to influence weight change (Carpenter et a l . , 1972). In th i s study the animals were maintained at an egual degree of fatness. To achieve t h i s the larger cows were fed l e s s , and naturally tended to gain less, than the smaller cows. This result was, therefore, the result of the feeding regime. Brown (1970) also reported that weight change was correlated with mean body weight. However, when weight change was expressed as a percentage of mean body weight the relationship was not s i g n i f i c a n t . Calf weaning weight A number of studies have found a s i g n i f i c a n t r e l a t i o n s h i p between cow weight change and c a l f weaning weight; the cause-and - e f f e c t r e l a t i o n s h i p between these two factors w i l l be 1 3 considered i n the discussion. Meanwhile previous research on t h i s i s described. Vacarro and D i l l a r d (1966) and Singh et a l . (1970) report a negative c o r r e l a t i o n . On the other hand, England et a l . (1961) found a positive c o r r e l a t i o n , in each of six 28-day periods, from which they concluded that good pasture conditions a f f e c t cow and c a l f weights s i m i l a r l y within periods. The c o r r e l a t i o n between these factors in d i f f e r e n t periods was, however, negative. The authors attributed t h i s to cows which increased in weight i n the e a r l i e r periods subseguently having poor milk production. Brinks et a l . (1962) and Jeffrey and Berg (1971) found no s i g n i f i c a n t r e l a t i o n s h i p between cow and c a l f changes in weight during the summer period. Sex of c a l f It has been reported that the sex of a c a l f has an influence on the milk production of i t s dam., Butledge et a l . (1971) report that dams nursing female calves produce s i g n i f i c a n t l y more milk than those nursing males. Pope et a l . (1968) found that cows nursing male calves had superior milk production. However, no reports exist on whether t h i s d i f f e r e n t i a l sex e f f e c t on milk production influences a cow's weight change during the suckling period. It i s apparent from t h i s l i t e r a t u r e that a cow's weight i s determined by a number of major factors. These are her age, her herd, her condition, her history of pregnancy and l a c t a t i o n , and the time of year at which she i s weighed. Certain other factors seem to be of lesser importance, v i z . her age at f i r s t c alving, month of calving and l i n e of breeding. In addition, year of b i r t h and degree of inbreeding have been reported to influence a 14 cow's weight, but t h e i r importance i s l i k e l y to be r e l a t i v e l y minor. There are fewer reports on the factors affecting a cow's weight change. Her age and the season through which the change takes place influences the magnitude and d i r e c t i o n of the change, but her breed and body weight are not important. Reports on the influence of the c a l f on a cow's weight change through the summer are inconsistent. A l l these s i g n i f i c a n t genetic and environmental fact o r s and th e i r interactions w i l l a f f e c t a cow's pattern of growth. Fitzhugh (1965), Fitzhugh et a l . (1967) and Brown et a l . (1972) found a considerable o s c i l l a t i o n in the weight of cows around th e i r mean growth curve. Joandet and Cartwright (1969) report that the body weight of one five-year-old cow, which had a mean weight of 1120 l b . , varied by as much as 40% i n a period of eight months. As a consequence of t h i s , they guestion the rationale of comparing the weights of cows taken at constant ages, unless the e f f e c t s of the environment have been established. Taylor (1965) also remarks that differences i n n u t r i t i o n and environment can be r e l a t i v e l y so great that the unqualified use of liveweight i n comparing breeds within a species or i n d i v i d u a l s within a breed becomes worthless. The work which has been covered i n t h i s review gives an ind i c a t i o n of the nature and significance of the environmental and genetic influences on cow body weight. Most of the data, however, were obtained from cow herds maintained at experimental stations, many of which are in the southern United States. There are no data from commercial herds and from c a t t l e i n northern 15 la t i t u d e s . 1 6 CHAPTER 3 Materials and Methods In t h i s study growth patterns are defined by changes i n body weight. The reasons for the use of body weight are as follows: 1) The measurement of body weight i s more precise than that of s k e l e t a l parameters. Consequently, the lack of repeatabity of s k e l e t a l parameters, which was reported i n the previous chapter, precludes th e i r use as v a l i d alternative or additional measures of growth. 2) Growth rate, a factor of major importance i n a beef production system, i s clo s e l y correlated with body weight. 3) Body weight i s the major determinant of a cow's nutrient reguirement and i s thus important j e r se. H) Body weight, in contrast to s k e l e t a l measurements, responds guickly to the environment and can be used e f f e c t i v e l y for the evaluation of both genetic and environmental factors a f f e c t i n g growth patterns. The decision to use f i e l d data was based on the rationale that the large sample of animals included in a f i e l d study i s l i k e l y to be more representative of the population of cows than the smaller sample which could be included in a controlled experiment. Thus the results obtained from a f i e l d study are more l i k e l y to r e f l e c t the s i t u a t i o n as i t exists i n the t o t a l population of cows. However, f i e l d research has some disadvantages: 17 1) Certain parameters cannot be investigated because s p e c i f i c treatments cannot be imposed on the animals. 2) The parameters which can be investigated cannot be controlled. 4) Cows are culled from the herds and new ones are introduced. 5) Herd owners may stop co-operating. 6) Fewer data can be c o l l e c t e d than i n a controlled experiment. These disadvantages were not, however, considered s u f f i c i e n t to preclude the f i e l d approach. The data were collected from ranches and farms in the province of B r i t i s h Columbia during the period from the f a l l of 1973 to the spring of 1976. The i n i t i a l approach to beef producers was by a l e t t e r in which the objectives of the study were explained and the i n d i v i d u a l was asked whether he would be interested in co-operating. These were mailed to: 1) A l l producers who were enrolled on the federal Record of Performance (Beef) Program. 2) A l l beef producers who had used the services of the major, l o c a l a r t i f i c i a l insemination service during the previous f i v e years. Positive r e p l i e s were received from 45 of the approximately 135 in d i v i d u a l s who were contacted. A ful l - t i m e technician was then employed to v i s i t each of these producers to discuss t h e i r p a r t i c i p a t i o n in the study. For a producer to part i c i p a t e , his operation had to s a t i s f y the following four prereguisites: 1) There was a scale on which to weigh the cows accurately. 2) The cows were a l l i d e n t i f i e d with a unique ear-tag, or other equivalent mark. 18 3) The dates of b i r t h of the cows (at least year and season) were known. 4) The calves were i d e n t i f i e d and t h e i r date of b i r t h , sex and dams i d e n t i t y were recorded. Additionally the producer was required to commit himself to the following procedures, for three years. 1) To weigh his cows each spring as soon as possible post-partum. 2) To weigh cows and calves each f a l l at weaning time. 3) To record the birth date, weaning date and sex of the calves. 4) To mail a l l these data to the author. The technician also asked the producers he v i s i t e d , and the l o c a l a g r i c u l t u r a l o f f i c e r s of the p r o v i n c i a l government, for names of ether producers i n the area whose operations s a t i s f i e d 'the c r i t e r i a mentioned above. Any such producers were also asked to co-operate in the study. As a result of the work of the technician from September to December 1973, approximately twenty-five producers agreed to co-operate. A small number of these were able to weigh at weaning time i n the f a l l of 1973. Most of the c a l f weaning weights recorded at t h i s and subseguent f a l l weighings were also included in the federal Record of Performance (Beef) Program. They were, therefore, recorded under the supervision of the l o c a l a g r i c u l t u r a l o f f i c e r of the p r o v i n c i a l government. During the winter of 1973/74 personal approaches were made by the author and Dr. John Hodges to e n l i s t the co-operation of a ranch with 650 cows which s a t i s f i e d the f i r s t three of the four prerequisites mentioned above. As the study progressed the 19 producer decided to i d e n t i f y the calves and record t h e i r dates of b i r t h , thus s a t i s f y i n g the fourth prerequisite. Additional co-operation was en l i s t e d from t h i s ranch to enable the cows to be weighed on two additional occasions during the winter. Contact with producers who had agreed to co-operate, was re-established by a v i s i t from a fu l l - t i m e f i e l d technician during the l a t e winter and spring of 1974. At the same time further potential co-operators were contacted. Spring-weight data were obtained fxom most of the herds which had been weighed the previous f a l l and from a number of new herds. The technician during t h i s period also extracted background data about each cow's history (such as the age and breed or cross of each cow being weighed and i t s pregnancy status i n 1973) from the breeding records for each herd. Subseguent to the spring of 1974 the author maintained contact with co-operating producers by l e t t e r s , phone and personal v i s i t s . However, as these i n d i v i d u a l s were widely distributed over an area which extended 650 miles to the north of Vancouver,B.C. and 550 miles to the east, personal v i s i t s were limited by the time available and the large distances to be t r a v e l l e d . Nevertheless, most of the co-operators were v i s i t e d at l east twice between the summer of 1974 and the spring of 1976. On these occasions the management practices of each herd were recorded and i t was ascertained that such practices were standard for a l l the animals in the herd. Further sets of data were collected i n the f a l l of 1974, the spring and f a l l of 1975, and the spring of 1976, The age and breed or cross of any new cows were recorded when they were 20 f i r s t weighed. The author was personally involved i n the recording cf cow weights at the 650-cow ranch. Here, i n addition to the regular spring and f a l l weighings, the cows were weighed in January of 1974, 1975 and 1976 and i n February of 1975 and 1976. The accuracy of the scale at t h i s ranch was checked by the author prior to each weighing session. On the other operations the accuracy of the scale was checked by the l o c a l a g r i c u l t u r a l o f f i c e r of the pro v i n c i a l government when he was present to weigh the calves each f a l l . When the data were f i n a l l y c ollated i t became apparent that there were nine herds which had been weighed regularly enough during t h i s three-year period to allow them to be included in an analysis of consecutive weight records. A general description of each follows. Herd J Breedtype;- Hereford (grade) Number of cows:- 135 Summer grazing:- range Farm/ranch l a t i t u d e : - 50° 40» North Farm/ranch elevation:- 1200ft. General location in B r i t i s h Columbia:- Southern I n t e r i o r Region Herd 2 Breedtype:- Hereford (grade) Hereford x Shorthorn Hereford x Angus 21 Number of cows:- 650 Summer grazing:- range Farm/ranch l a t i t u d e : - 50° 30' North Farm/ranch elevation:- 1600ft. General location i n B r i t i s h Columbia:- Southern In t e r i o r Region Herd 3 Breedtype:- Hereford (grade) Number of cows:- 150 Summer grazing:- range Farm/ranch l a t i t u d e : - 52° 0' North Farm/ranch elevation:- 2900ft. General location in B r i t i s h Columbia;- Chilcotin/Cariboo Region Herd 4 Breedtype:- Hereford (grade and purebred) B r i t i s h breed crosses Limousin crosses (<50% Limousin) Simmental crosses (<50% Simraental) Charolais crosses (<50% Charolais) Chianina crosses (<50% Chianiria) Number of cows:- 150 Summer grazing:- range Farm/ranch l a t i t u d e ; - 50° 30' North Farm/ranch elevation:- 2800ft. General location in B r i t i s h Columbia:- Kootenay Region Herd 5 22 Breedtype:- Hereford (grade) Limousin crosses (<50% Limousin) Charolais crosses (<505& Charolais) Number of cows:- 60 Summer grazing:- grass pasture - no i r r i g a t i o n Farm/ranch l a t i t u d e : - 50° 10* North Farm/ranch elevation:- 1800ft. General location i n B r i t i s h Columbia:- Kootenay Region Herd 6 Breedtype:- Aberdeen Angus (purebred) Number of cows:- 20 Summer grazing:- grass pasture - no i r r i g a t i o n Farm/ranch l a t i t u d e : - 49° 20* North Farm/ranch elevation:- 300ft. General location i n B r i t i s h Columbia:- Lower Mainland Region Herd 7 Breedtype:- Hereford (purebred) Number of cows:- 45 Summer grazing:- grass and a l f a l f a pasture - p a r t i a l l y i r r i g a t e d Farm/ranch l a t i t u d e : - 51° 0* North Farm/ranch elevation:- 2200ft. General location i n B r i t i s h Columbia:- Southern I n t e r i o r Region Herd 8 Breedtype:- Hereford (grade and purebred) Hereford x Angus 23 Number of cows:- 120 Summer grazing:- range Farm/ranch l a t i t u d e : - 54° 0' North Farm/ranch elevation:- 2300ft. General location in B r i t i s h Columbia:- Central Region Herd 9 Breedtype:- Hereford (grade) Simmental crosses (<50% Simmental) Charolais crosses (<50% Charolais) Number of cows:- 35 Summer grazing:- grass and a l f a l f a pasture - p a r t i a l l y i r r i g a t e d Farm/ranch l a t i t u d e : - 49° 40« North Farm/ranch elevation:- 2700ft. General location in B r i t i s h Columbia:- Kootenay Region Management practices were the same for each herd, i . e . spring calving, summer grazing, f a l l weaning and winter feeding on silage and/or hay. The winter feeding period normally extended from October/December u n t i l April/May and was determined by the l a t i t u d e and elevation of the summer grazing. The major difference between the herds was that f i v e of them (as mentioned above) u t i l i z e d summer rangeland while four used summer pasture - two of which were p a r t i a l l y i r r i g a t e d . The guality of summer range was observed by the author to vary between ranches, but no attempt was made to guantify these differences. With the exception of some of the older cows i n herd 7, a l l the cows were spring-born and calved for the f i r s t 24 time at two years of age. A l l the cows in a herd were subject to the same management practices. Apart from minor adjustments i n response to f i n a n c i a l and climatic f a c t o r s , these were the same from one year to the next. Such minor 'within herd, between year' management differences, and any minor differences between herds, w i l l be described as they become relevant i n the Discussion. 25 C H A P T E R 4 S t a t i s t i c a l Analysis A basic precept of accurate s t a t i s t i c a l analysis i s the formulation of precise and complete mathematical models. To enable e f f i c i e n t and va l i d estimates of the eff e c t s to be calculated, a l l s i g n i f i c a n t sources of var i a t i o n should be included in a model. In t h i s research separate models w i l l be formulated f o r the following dependent variables: 1) Cow weight in the spring (post-partum) and f a l l (at weaning). 2) Changes i n cow weight a) during the summer, b) during the winter. The change i n weight w i l l be considered as a percentage of the mean weight during the period under consideration. 3) Cow weight in one herd in the f a l l and on two occasions during the winter (winter analys i s ) . The independent analyses for the weight changes are considered necessary for the following reasons: 1) The a b i l i t y to include , additional parameters in these analyses which are s p e c i f i c to one or other of the weight changes. 2) The physiological effect of, for example, a 100 l b . change in weight i s l i k e l y to d i f f e r between a small and a large cow. By considering each change on a percentage basis such a difference can be included i n the analysis. Previous research has shown that the following parameters ^  26 or independent variables might affect the above dependent variables, (* = anticipated as being p o t e n t i a l l y s i g n i f i c a n t and b i o l o g i c a l l y meaningful i f s i g n i f i c a n t ) . Cow Weijght winter Chancje i n Weicjht Msiaht Summer Jinter Breedtype of the cow Age of cow Herd of the cow Year of recording Date of recording Spring i n t e r v a l Age at f i r s t calving Genotype of the cow Pregnancy and l a c t a t i o n status in the year of record Pregnancy and l a c t a t i o n status in the previous year Birth year of the cow Season of b i r t h of the cow Condition of the cow Body weight Previous change in weight Calf age at weaning Calf weaning weight Sex of c a l f Days pregnant * * * * * * * Where they are relevant, these factors should, therefore, 27 be considered for in c l u s i o n i n the models for the analysis the dependent variables. The rationale for including them in excluding them from the models for the present analyses discussed below. A cow w i l l (despite seasonal fluctuations) increase i n weight u n t i l she reaches maturity. Age i s , therefore, included i n the models for the analyses of absolute body weight (weight) and seasonal weight change (weight change). Breedtype The mature weight and age of a cow are dependent on her breed, or, for a crossbred cow, her breed composition. In herds of more than one breedtype, t h i s e f f e c t i s included i n the models for the analyses of weight and weight change. In a herd of a single breedtype i t i s confounded with the Herd E f f e c t . The breedtype of each i n d i v i d u a l cow in the largest herd in t h i s study i s not known. The omission of t h i s effect inevitably increases the residual error in the analysis. However, i t was f e l t that the inclusion of the large number of cows from t h i s herd would more than offset t h i s disadvantage. Herd The feeding management, breeding management, range management and ether factors unigue to a herd w i l l only a f f e c t the weight and weight change of the cows in that herd. In t h i s study the cows in any herd are a l l treated a l i k e , each herd i s therefore considered as a single unit. The Herd E f f e c t , which i s included in the model "for each analysis, also includes the of or i s 28 following factors: 1) Location - in respect of climate, range/pasture g u a l i t y , winter feed guality. 2) In herds of a single breed, the Breedtype Effect. Year of recording In a herd the environmental e f f e c t , e.g. climate, feed quality and management practices, might vary between years. A Year Effect i s , therefore, included in the models for the analyses of weight and weight change. Date of recording The a v a i l a b i l i t y of feed, the climatic conditions and the pregnancy and l a c t a t i o n status of a cow w i l l affect her weight and weight change. The ef f e c t of these i s dependent on the time of year (date) at which she i s weighed. It i s , therefore, included in the model for the analysis of cow weight as a Season E f f e c t . In the winter weight analysis the observations are c l a s s i f i e d by the number of days the cow i s pregnant at the date of recording. They are thus independent of th i s factor. Spring i n t e r v a l The i n t e r v a l between calving and weighing in the spring i s more variable than the i n t e r v a l from weaning to weighing i n the f a l l . If cows lose or gain weight during t h i s i n t e r v a l i n the spring, the weight at the time of recording i s a poor estimate of her weight immediately post-partum. A Spring Interval Effect cannot, however, be included as an independent variable i n the analysis f o r the absolute weights. In the analysis f o r summer weight change i t i s confounded with the Previous Weight Change Eff e c t (see later) and also cannot be included. I t i s , however. 29 included in the analysis for winter weight change. As there i s known to be no c o r r e l a t i o n between age and spring i n t e r v a l (r=0.07), i t w i l l not be f i t t e d independently i n each age subclass. Data which have a spring i n t e r v a l long enough to have a s i g n i f i c a n t e f f e c t on winter weight change in a preliminary, i n d i v i d u a l herd analysis are removed from a l l subseguent analyses. Acje at f i r s t calving The stress of pregnancy and l a c t a t i o n might cause a cow which f i r s t calves at two years of age to be l i g h t e r than one which was older at f i r s t calving. In eight of the nine herds i n t h i s study the cows f i r s t calved at two years of age. In the other herd a number of cows over six years of age calved for the f i r s t time i n the spring at two and a half years of age. For these f a l l - b o r n cows the Age of F i r s t Calving and Season of Bir t h (see later) E f f e c t s are, therefore, confounded. They are included i n the model for the weight analysis of this herd as an Age of F i r s t Calving Effect. Genotype The weight and, possibly, weight change of a cow i s influenced by the gametes contributed by her s i r e and dam, i.e. by t h e i r genotypes. However, a lack of breeding records prevents th e i r inclusion i n the models for the present analyses. £i63£ aS£I and l a c t a t i o n status in the .year of record A cow without a c a l f can direct a l l the feed she consumes to her body tissue, instead of to milk production and/or the foetus. Such a cow w i l l , thus, have a d i f f e r e n t weight and weight change in comparison to a suckling and/or pregnant cow. 30 This research i s concerned with the weight and weight change of the pregnant beef cow. Therefore, the spring and f a l l weight records of cows which were not pregnant and the f a l l weight records of cows which gave b i r t h to a c a l f but did not wean i t are excluded from the analyses. Pregnancy, and l a c t a t i o n in the previous v.ear The e f f e c t described immediately above can have a carry-over e f f e c t from one year to the next. Therefore, once a cow does not wean a c a l f (including those not weaning a c a l f in 1973), a l l her subseguent records are excluded from the analysis. A lack of calving records in the largest herd i n t h i s study prevented any exclusion of these cows on the basis of past or present pregnancy and l a c t a t i o n status. Their inclusion i n e v i t a b l y increases the residual error i n the analysis. However, i t was f e l t that the inclusion of the large number of cows from t h i s herd would more than offset t h i s disadvantage. Year of b i r t h Genetic or environmental factors unique to the year of b i r t h of a cow might have an influence on her weight. Previously guoted research has shown thi s e f f e c t to be r e l a t i v e l y small. Therefore, i t i s here assumed to be random and i s allowed to contribute to the residual variance. Season of b i r t h In a l l but one of the herds in t h i s research study the cows were born i n the spring. In the other herd some of the older cows were born i n the f a l l and calved for the f i r s t time at two and a half years of age. As previously mentioned, t h i s j o i n t 31 Season of Birth /Age at F i r s t Calving Effect i s included i n the model for the analysis of weight in t h i s herd. Condition Previous research has shown that t h i s affects the weight of a cow. I t could also affect the weight change of a cow - a • f a t t e r ' cow might be expected to have a greater weight loss, or les s weight gain, than a 'thinner' cow. Condition i s a subjective character and the problem of c l a s s i f y i n g i t was reported previously. The problem of recording the i n t r i n s i c a l l y more variable body measurements which r e f l e c t body condition was also mentioned. The advantage which might be gained from including one or other of these estimates of condition i n the present analysis i s considered to be i n s u f f i c i e n t to offset the r i s k of the increase in the error factor which could r e s u l t from t h e i r i n c l u s i o n . It i s not, therefore, included i n for the present analyses. Body weight If body weight r e f l e c t s condition i . e . a ' f a t' heavy one, and vice versa, the body weight of a influence her weight change. However, the correlat e x i s t s between the age of a cow and her body weight pr inc l u s i o n of t h i s factor i n the models for the wei analyses. Previous change i n weight A cow w i l l have a c h a r a c t e r i s t i c mean weight whic dependent on her age, breedtype, herd etc. I f environmental factors cause her actual weight to dev t h i s , a subseguent compensation i s l i k e l y to occur t the models cow i s a cow could ion which events the ght change h w i l l be short-term i a t e from o cause i t 32 to return towards i t s expected or true mean. Thus, a change in weight in one period i s influenced by the weight change i n the previous period. This compensatory growth i s , however, l i k e l y to d i f f e r between age subclasses. In a younger cow a weight gain r e f l e c t s a growth of muscle and, to a lesser extent, s k e l e t a l tissue, and such weight gain i s not e a s i l y l o s t . In older cows weight changes r e f l e c t changes i n condition and thus weight can be gained and l o s t r e l a t i v e l y e a s i l y . Therefore, t h i s previous change in weight parameter w i l l be f i t t e d independently i n each age subclass i n the models for the analyses of weight change, weight ft heavy c a l f weaning weight i s p a r t i a l l y a product of a high milk production by i t s dam. In comparison with a l e s s productive contemporary, a cow with a heavy c a l f might d i r e c t more of the feed she consumes to milk production. In the less productive animal i t i s more l i k e l y to accumulate in her body tis s u e . This difference i n •lact a t i o n stress* might be reflected i n a cow's f a l l weight. In the analysis of the spring and f a l l weights i t i s confounded with the Season E f f e c t and i n the analysis of winter change in weight i t i s confounded with the previous weight change. A lack of weaning weight data prevents i t s i nclusion in the model for the winter analysis. Therefore, a Weaning Weight Eff e c t w i l l only be included i n the model for the summer weight-change analysis. Calf age at weaning A cow which has a r e l a t i v e l y old c a l f i s l i k e l y to be producing less milk than one with a younger c a l f . This i s a product of the f a c t that: 33 1) She i s at a l a t e r stage i n her l a c t a t i o n . 2) The c a l f i s suckling her less. A cow with an older c a l f at weaning w i l l , therefore, have had more time to overcome the 'lact a t i o n stress* mentioned above than a contemporary with a younger c a l f . Her f a l l weight might r e f l e c t t h i s . As with weaning weight, t h i s Calf Age Eff e c t w i l l only be included in the model for the summer weight-change analysis. Sex of c a l f A d i f f e r e n t i a l effect of the sex of a c a l f on the milk production of i t s dam was mentioned previously. This might, owing to a d i f f e r e n t i a l Mactation s t r e s s 1 , influence the weight change of a cow. Sex of c a l f w i l l , therefore, be included i n the model for the analysis of summer weight change. Day_s pregnant The weight of a cow during pregnancy w i l l r e f l e c t the increase in the weight of the foetus and i t s associated tissues and f l u i d s . At the time of weighing i n the spring a cow i s empty, i n the f a l l the weight of the foetus etc. w i l l be minimal. It i s , therefore, considered to be of i n s u f f i c i e n t importance to warrant i t s in c l u s i o n in the models for the analysis of spring and f a l l weights and weight change. However, i n the winter weight analysis i t s influence i s l i k e l y to be s i g n i f i c a n t . The increase i n weight of the concepfus i s hot l i n e a r over time, therefore, the number of days a cow i s pregnant and i t s sguared and cubed values are included i n the winter analysis. The date of conception for a cow i s calculated by subtracting 285 days, the mean length of pregnancy for 3 4 B r i t i s h beef breeds quoted by Preston and W i l l i s (1960), from her calving date. Days pregnant i s then the i n t e r v a l i n days between t h i s date and that of weighing. The f i r s t order interactions amongst the independent variables to be considered are also included in the models for the analyses. Higher order interactions are considered as having i n s u f f i c i e n t b i o l o g i c a l meaning to warrant consideration. Once the parameters to be included have been decided, the next step i s to define the nature of the models which are to be analysed. Eisenhart (1947) defines two 'types 1 of models; the •type' of model i s dependent on the class of variables to be analysed. Type 1 Model - i n which 'the estimation i s of a fixed , relationship among means of sub-sets of the universe of objects concerned*. Type 2 Model - i n which 'the estimation i s of components of (random) variation associated with a composite population.. i.... from the population of possible i n d i v i d u a l s ' . These he c l a s s i f i e d as 'fixed effects* and 'random effects* models respectively. The i n i t i a l computational procedures and the mechanics of the te s t s of significance are the same for the Analysis of Variance (ANOVA) for each model. Interpretation of the ANOVA, however, depends on the type of model. Eisenhart (1947) also mentions the 'mixed* model, i n which there are both fixed and random e f f e c t s . This model and methods for handling 35 i t s analysis are discussed i n more d e t a i l by Henderson (1953) and Searle and Henderson (1961). Eisenhart (1947) defines a fixed e f f e c t as being composed of d i s t i n c t sub-sets, he also states that any conclusions from a fixed e f f e c t analysis must be confined to the s p e c i f i c e f f e c t s included in i t . In t h i s analysis herd, year, season, breedtype and sex of c a l f s a t i s f y these c r i t e r i a . They are thus fixed e f f e c t s and the model used for th e i r analysis i s Eisenhart*s Type 1. It could be argued, however, that the herds, years, genotypes and ages, e s p e c i a l l y the l a s t , were a random selection from the populations of these e f f e c t s . This view would reguire use of a Type 2 model. However, i n t h i s study these e f f e c t s are viewed i n Eisenhart*s terminology as being the 'universe* about which dire c t conclusions are drawn. They are also composed of d i s t i n c t sub-sets, amongst which comparisons are to be made. For these reasons they are considered as fixed e f f e c t s . The remaining independent variables, v i z . previous weight change, spring i n t e r v a l , days pregnant, c a l f age and weaning weight, are considered as random effec t s . Their influence on the dependent variable i s removed by the use of covariance. This allows the fixed e f f e c t s to be measured with greater precision. Since Fisher (1925) f i r s t formulated the analysis of variance, many modifications have been devised to increase the scope of i t s application. These have included i t s application to data with unegual subclass freguencies (Harvey, 1975). The confounding of effects which results from such non-orthogonal data can be overcome by considering a l l the e f f e c t s 36 simultaneously. Least-squares methods of analysis allow t h i s to be done, and are used here. Yates (1934) proposed a method of analysing fixed e f f e c t s by ' f i t t i n g constants', analagous to the method of regression when the independent variables assume the values of 0 or 1. Harvey (1975) describes in d e t a i l the use of t h i s method. For a fixed e f f e c t s model t h i s provides for the computation of means, regression c o e f f i c i e n t s , standard errors, tests of s i g n i f i c a n c e , orthogonal polynomials and the sum cf sguares of differences between components of' an e f f e c t . A general outline of the analysis described by Harvey (1975) follows: 1) The formulation of l e a s t sguare eguations. 2) The reduction of these eguations by imposing the appropriate r e s t r i c t i o n s - normally that the sum of the constants within a given set egual zero. 3) The solution of these n equations i n n unknowns. This i s done by inverting the variance/covariance matrix. Each constant i s then egual to the sum of the products of the inverse elements of the variance/covariance matrix for a constant and i t s Right Hand Member (R.H.M., the numerical value of i t s equation). 4) The computation of t o t a l sum of squares (total S.S.), reduction S.S. (from the sum of products of the constants and th e i r R.H.M.) and the residual S.S. (by difference). 5) Computation of the sums of sguares of differences between components of a set. These are obtained from the product of the constant estimates for a given set and the i r corresponding inverse segment of the variance/covariance matrix. 37 6) The computation of the standard errors of the constants. These are obtained from the product of the residual mean sguare and the inverse diagonal element of the variance/covariance matrix for the constant. 7) The computation of the reguired comparisons. The least squares analysis used in this research i s a modified version of the above. It was carried out using a generalised least squares subroutine, developed by Peterson (1974). The analysis package was written in Fortran IV and was used on a I.B.M. system/370, model 168, computer. A general outline of t h i s analysis follows: 1) The formulation of the least sguares equations - with the sum of the constants of a given set egualling zero. 2) Computation of the sum of sguares and cross-product matrix -from 1) by absorbing y row and column. 3) The computation of the variance/covariance matrix - from 2) by dividing by the t o t a l degrees of freedom. 4) The computation of the co r r e l a t i o n matrix - from 3) by dividing by the geometric mean of the variance. 5) The computation of the inverse of the correlation matrix. 6) The computation of the inverse of the variance/covariance matrix, i n which the i j t h element (C_) i s obtained as follcws:-x ( 1 / ( V l i ) - 5 ) x ( 1 / ( V J V 5 ) x (l/W 1 1-!) where the i j t h element of the inverse of the c o r r e l a t i o n matrix. 38 VXJ" = the variance of the 1th e f f e c t which are the diagonal elements of the variance covariance matrix. - the t o t a l number of observations, 7} The computation of the t o t a l S.S, the reduction S.S and, by difference, the residual S.S. The reduction S.S i s calculated as fellows: 2 Seduction S.S. = Total S.S. x R-sguare complete model (Rn) where R 2 = E b' . .x r i n n n i . j (b = the standard p a r t i a l regression c o e f f i c i e n t of the i t h n i . j independent vaiable holding a l l other independent variables constant and r l n = the correlation between the i t h independent variable and the nth dependent variable, from the c o r r e l a t i o n matrix). 8) The computation of constants - from the product of the standardised p a r t i a l regression c o e f f i c i e n t and the r a t i o of the standard deviations of the dependent and independent variable being considered. 9) The computation of t h e i r standard errors - as i n Harvey (1975) . 10) The computation of constants and standard errors f o r the absorbed independent variables. 11) The computation of the sums of sguares of differences between means - as i n Harvey (1975). The maximum number of degrees of freedom which can be f i t t e d i n a model i s limited by the precision of the inversion 39 of the co r r e l a t i o n matrix. This i s a product of the rounding errors which occur i n th i s inversion. Previous experience has shown that the upper l i m i t i s approximately one hundred and f i f t y degrees of freedom. As a resu l t of the above rat i o n a l e , the following models are used in the analyses, 1) Cow weight in the spring and f a l l Y. , = y + B. +A. + H. + R., + S + (interactions) + e. ., , xjklmn x j k 1 m i j k l m n i n which Y. ., , = the record of a cow's weight on a particular occasion i j k l m n of weighing. y = the o v e r a l l mean-common to a l l cows when the sum of each set of discrete variables in zero, B i = the effect of the i t h breedtype. Aj = the effect of the jth age. E = the effect of the kth herd. k R-j^  •= the eff e c t of the 1 th year. S = the effect of the mth season. m (interactions) = the f i r s t order interactions amongst these discrete independent variables. e. , = the random error associated with the Y th record i j k l m n i j k l m n 2a) Change i n cow weight during the summer 4 t 1 = y + B. + A. + H • fi + S + (interactions) + xjklmn x J _k 1 m _ bT-(W. . - W) + b (C - C) + b (P - Pj • e 1 i j k l m n 2 i j k l m n 3 i j k l m n i j k l m n i n which Y. ., . = the summer weight change record, xjklmn 3 40 y - the o v e r a l l mean. B i = the eff e c t of the i t h breedtype. A = the eff e c t of the jth age. H k = the effect of the kth herd. R-L = the eff e c t of the 1th year. S m = the effect of the mth sex of c a l f . (interactions) = the f i r s t order interactions amongst these discrete independent variables. b-^ = the regression of the dependent variable on the weaning weight of the c a l f . b 2 = the regression of the dependent variable on the age of the c a l f , b 3 = the regression of the dependent variable on the previous weight change of the cow. e i j k l m n ~ t h e r a n ^ o m error associated with the ^ i j k i n m t h record. 2b) change i n cow weight during the winter Y i j k l m = y + B i + A j + Mk + 8 l + (interactions) + l > i < s i j k l i n - S) + b 2 < P i j k l m " P> + e i j k l m i n which 7 i j k l m = t n a w i n t e r weight change record, y = the o v e r a l l mean. B± - the effect of the i t h breedtype. Aj = the e f f e c t of the jth age. H, = the effect of the kth herd. k R1 = the e f f e c t of the 1th year. (interactions) = the f i r s t order interactions amongst these discrete independent variables. 41 b 1 = the regression of the dependent variable on spring i n t e r v a l . b 2 = the regression of the dependent variable on the previous weight change of the cow. e. ., , = the random error associated with the Y . ., th record. 3) Cow weight during the winter Y. ., = y + a . + A . + (interactions) b (DP - DP) + b (DP2 i j k i J 1 i j k ' 2 i j k - DP2) + b 0(DP 3.., - "DP3) • e. ., 3 i j k i j k i n which Y . = the record of a cow's weight on a particular occasion i j k during the winter, y = the o v e r a l l mean. EL = the e f f e c t of the jth year. A j - the effect of the kth age. (interactions) = the f i r s t order interactions amongst these discrete independent variables, b-^  = the regression of the dependent variable on the number of days pregnant(D.P.). - b 2 = the regression of the dependent variable on (D.P) 2* b 3 = the regression of the dependent variable on (D.P.) 3. a. ., = the random error associated with the Y , th record. I J K X j k The analyses using these models was f i r s t carried out on a within herd basis. The sums of sguares accounted f o r by the e f f e c t s f i t t e d in each herd were noted. The f i n a l formulation of the models for the combined analyses was based on these r e s u l t s . In order to test the s t a t i s t i c a l v a l i d i t y of combining the 42 data from the herds into such combined analyses, B a r t l e t t ' s test for homogeneity of variance was applied to the Residual Mean Sguares from the within herd analyses. The decision to include or exclude a herd from a combined analysis was made from the res u l t s of t h i s t e s t , together with the b i o l o g i c a l i nterpretation of the within herd analyses. The r e s u l t s of these analyses are given i n the following chapter. The influence of a parameter i n an analysis i s considered s i g n i f i c a n t i f P<0.05. 43 CHAPTER 5 Results Spring and F a l l weight The model for t h i s analysis can be f i t t e d to the spring and f a l l weight records from a l l nine herds. However, for the following reasons herd 9 i s excluded from the combined herd analysis: 1) The variance i n t h i s herd (20042) i s d i s t i n c t l y d i f f e r e n t from the variances of the other herds - t h e i r arithmetic mean i s 9384 (±1589). 2) In the analyses of i n d i v i d u a l herds the Breedtype Effect i s s i g n i f i c a n t only in t h i s herd. The remaining eight herds do not have homogeneous variances when tested with B a r t l e t t ' s test. However, the magnitude of the differences between them were not excessive when considered i n b i o l o g i c a l terms. They are, therefore, a l l included i n a combined analysis. Since the Breedtype Effect was not s i g n i f i c a n t when f i t t e d i n the i n d i v i d u a l analyses f o r herds, i t i s not included i n the model for the combined analysis. Similarly the Age at F i r s t Calving/Season of B i r t h Effect reguired for the weight records of herd 7 i s also excluded. The ANOVA of the records from these eight herds i s shown i n table 3. The least sguares estimates of the means of the subclasses i n the analysis are shown in table 4, the least 44 squares constants from which they are calculated are in appendix 1. The Herd Effect i s s i g n i f i c a n t and the means of each herd are shown in f i g 1. The following single degree of freedom comparisons were carried out (the herd numbers are shown i n parentheses) . Comparison F-value pasture (5-7) . v.range (1-4+8) 266.5 Herd 3.v.other range herds 926.9 Range herd comparisons (excluding herd 3) crossbred (2+4+8) .v. straightbred(1) 30.2 Exotic crossbred(4) . v. B r i t i s h crossbred (2+8) 2.6 PS.§iSI® herd comparisons crossbred (5) .v. straightbred (6+7) 24.86 Hereford (7) . v. Angus (6) 0.24 Thus, cows in pasture herds (weighted mean = 1090.5 lb.) are s i g n i f i c a n t l y heavier than those i n range herds (weighted mean = 971.5 l b . ) . Herd 3 i s s i g n i f i c a n t l y l i g h t e r than the other range herds and i s not included i n the other comparisons between range .herds. The mean weight of cows in the crossbred range herds (980.2 lb.) i s s i g n i f i c a n t l y less than that of the cows in the straightbred range herd (1030.5 l b . ) . However, amongst the pasture herds the cows i n the crossbred herd are s i g n i f i c a n t l y heavier (1104.4 lb.) than those i n the R-sguare 0.080 s i g . 0.068 s i g . 0.002 s i g . 0.000 N.S. 0.002 s i g . 0. 000 N.S. AoalJtsis of Variance Spring and F a l l Bgdj^ Weights Source Herd Age Year Season Herd x Year Herd x Sn. Herd x Age Age x Year Age x Season Yr x Season Residual d.f. jMean Sguare I H + 7 •9 2 1 14 7 59 18 8 2 5187 1606284 | 1332069 | 8219 | 3869523 I 124576 854873 59994 22337 1 19543 226917 8596 I F-value 186. 86* | 0.096 154. 96* | 0.103 0. 96 | 0.000 450.15* j 0.03 3 14. 49* } 0.015 99. 45* | 0.051 6. 98* j 0.033 2. 60* | 0.004 13. 90* j 0.008 26. 40* | 0.004 ! 0.382 R-sguare (* = effect s i g n i f i c a n t ) Total S.S. = 0.1168061E+9 Reduction S.S.= 0.7221858E+8 R-sguare = 0.618 % of Total S.S. assigned to parameters = 34.4 TABLE 4 46 i£ast Sguares Estimates for subclass Herd 1 2 3 4 5 6 7 8 Year 1 2 3 Sering arid F a l l Weights JSJLS_J_ estimate subclass 1030.5 971.2 865.1 995.4 1 104.4 1075.4 1083.3 1029.6 (672) * (2612) (654) (493) (223) (88) (247) (3 26) 1016.5 (1299) 1024.2 (2179) 1017.4 (1837) Age 1 2 3 4 5 6 7 9 10+ F a l l Spring L^S^ estimate 847. 870, 950, 1020, 1057, 1083. 1075. 1090, 1109.7 1086. 5 1076.5 962. 2 ,3 ,9 6 2 7 9 9 9 (134) (685) (759) (706) (597) (508) (327) (268) (268) (783) (2752) (2563) Age x Year Year 1 2 3 Age 2 871.6 863.2 877.8 3 946.9 972.4 932.3 4 1030.7 1020.4 1009.7 5 1051.6 1065.7 1055.9 6 1064.7 1093.3 1093.6 7 1064.2 1078.7 1084.7 8 1093.0 1094.6 1085.2 9 1108.7 1110.6 1109.8 10+ 1077.2 1095.8 1086.3 Herd x Year Year 1 2 3 Herd 1 973.5 1066.3 1051.8 2 986.4 949.3 978.0 3 841.5 872.2 881.6 4 1017.3 1001.0 967.8 5 1126.4 1103.3 1083.7 6 1039.9 1093.4 1092.7 7 1105.4 1085.5 1059.1 8 1041.2 1023.1 1024.5 Herd x Age Herd 1 2 3 4 Age 2 928.8 775. 4 793.9 871.4 3 947.8 865.6 794.6 943.3 =number of observations shown i n parentheses) TABLE 4 cent 4 1027.2 5 1067.8 6 1096.2 7 109-1. 3 8 1074.8 9 1087. 1 10 + 1106.3 Herd 5 Age 2 936.9 3 1045.3 4 1099.4 5 1147.2 6 1190.3 7 1147.0 8 1135.3 9 1202.5 10 + 1135.6 A3§. x Season Season Age 2 3 4 5 6 7 8 9 10 + iiS£d x Season Season Herd 1 2 3 4 5 ' 6 7 8 Year x Season Season Year 1 2 3 972.8 99 8. 5 1018.5 1050. 2 1079.2 1081. 6 1071.2 6 970.3 1082.5 1078.3 1126.3 1178. 8 1063. 9 1181.7 1062.8 868.4 899. 0 916.7 924. 4 913.3 920.7 926.4 7 779.9 984. 1 1075. 5 1104. 1 1135. 0 1166.1 1209.2 1228.0 1227.0 1032.5 1060.7 1061.5 1068.2 1050.5 1042.0 1012.0 8 910.6 941. 3 1007. 9 1058. 3 1075. 0 1096. 0 1118. 1 1097. 5 1079. 0 Spring 801.4 863. 3 952.0 1001.9 1036.9 1027. 2 1036.3 1064.8 1048.4 F a l l 940.4 1037.8 1088.3 11 13.6 1130.8 1124.6 1145.5 1154.6 1124.6 F a l l 1009. 5 S88.9 991.2 1060.8 1191. 3 1101.6 1131.3 1137.0 Spring 1051.6 953.6 . 739. 1 930.1 1017.3 1049.0 10 35.3 926.2 F a l l 1051. 9 1085.6 1091.9 Spring 981.0 962.8 942.9 The weight of the cows i n each herd. 1 2 3 4 5 6 7 8 Herd 49 straightbred herd (1081.6.1b.). These straightbred pasture herds consist of one Hereford herd and one Angus herd. The cows i n the former (1083.3 lb.) are not s i g n i f i c a n t l y different i n weight from those i n the l a t t e r (1075.3 l b . ) . Amongst the crossbred range herds the mean weight of cows in the herd containing exotic crossbreds (995.4 lb.) i s not s i g n i f i c a n t l y d i f f e r e n t from the mean weight of cows i n the herds which have only crossbreds of B r i t i s h breeds (977.7 l b . ) . Although these comparisons have been c l a s s i f i e d by the breedtypes or range/pasture type of the herds, they also r e f l e c t a l l the ether components of the Herd Effect which were mentioned in Chapter 5. The Age Effect i n the ANOVA i s s i g n i f i c a n t . The pattern of the increase in weight over age i s shown i n f i g 2. Both the l i n e a r (E2=0.001) and quadratic (H2=0.019) components of th i s increase in weight are s i g n i f i c a n t . From a weight of 870.9 l b . at two years of age, the weight of a cow i n i t i a l l y increases rapidly. The rate of increase then slows, but continues through to 9 years of age. The increase in weight from the mean of ages six and seven to nine i s s i g n i f i c a n t , but the difference i n weight between nine-year-old cows (1109.7 lb.) and ten-year-old (1086.5 lb.) cows i s not. The Year Effect i s not s i g n i f i c a n t , the largest difference between the years being only 7.7 l b . However, within each year, the Season Eff e c t i s s i g n i f i c a n t . Cows are on average 114.2 l b . heavier i n the f a l l than in the spring. The Age/Year and Age/Season inte r a c t i o n s are s i g n i f i c a n t s t a t i s t i c a l l y , but t h e i r R 2~values show that t h e i r b i o l o g i c a l s i g n i f i c a n c e i s minimal. The mean summer and winter weight 50 The Increase in weight over age. 50a (sqi) w6i9M MOO 51 changes which can be calculated from the Age/Season i n t e r a c t i o n subclass means are shown in table 5. The difference between the mean winter weight loss of these estimates and the main seasonal ef f e c t i s an i n e v i t a b l e product of the least squares analysis. The difference between the outer two weight estimates (two-year-olds i n the spring and ten+-year-olds i n the f a l l ) i s absorbed into the winter change i n weight estimates. These seasonal fluctuations around the mean pattern of growth are shown in f i g 3. In comparison to the summer weight changes, the values of the winter weight change are more si m i l a r across ages. The summer weight gain i s greatest in younger cows (ages 2 to 5) . Amongst these younger cows, the weight gain of three-year-old cows (174.5 lb.) i s 27% greater than the mean gain of two and four-year-old cows (137.8 l b . ) . The Year/Season in t e r a c t i o n i s also s i g n i f i c a n t s t a t i s t i c a l l y , but again i t s b i o l o g i c a l importance i s small. The mean summer and winter weight changes i n each year are shown i n table 6. As explained above, the difference between the mean summer weight gain of these estimates and the main seasonal e f f e c t i s an inevitable product of the least sguares analysis. The two summer weight gains are eguivalent to each other, as are the two l a t e r winter weight losses. The smaller weight loss i n the winter of 1973/74 i s mostly a product of the herds which were recorded over t h i s period. The Herd/Year i n t e r a c t i o n i s s t a t i s t i c a l l y s i g n i f i c a n t and accounts for considerably more of the variation amongst the weight records than the interactions mentioned previously. However, only three of the in t e r a c t i o n deviation constants are TABLE 5 Seasonal Weight Cja^gesjlbj. i n each Age Subclass I I Age I Summer Weight Change J Winter Weight Change 1 2 | 139.0 i i 1 3 j i i 174.5 1 1 1 4 1 136.6 1 1 i 5 | i i 111.7 I I i 6 J 93.9 I 1 1 7 J i i 97.4 I ] I 8 | l i 109.2 l 1 1 9 1 89.8 1 I } 10+ | i i 76.2 I 1 L _ . j -77.1 -85.8 -86. 7 -76.7 -103.6 -88.3 -80.7 -106.2 TABLE 6 Seasonal Weight Changesjlb), i S sach Year i I Winter Year 1 | 1 -70.9 i I Summer Year 1 | 104.6 j j Winter Year 2 j -122.8 j j Summer Year 2 | 129.1 j J Winter Year 3 | -149.0 J 53 Figure 3 The seasonal fluctuations i n weight around the mean growth curve. 54 greater than 30 l b . , two of these being in herd 1. In t h i s herd there was a mean weight increase of 92.8 l b . betweeen year 1 and 2, with 14.6 l b . of this being l o s t i n year 3. This point w i l l be discussed l a t e r . When the means for the other herds are compared over years, two of the herds were lig h t e s t in year 1, two were l i g h t e s t in year 2 and three i n year 3. Thus, excluding herd 1, the year of record appears to be and i s considered as a random variable. The Herd/Season i n t e r a c t i o n i s also s i g n i f i c a n t . The proportion of the variance accounted for by t h i s interaction exceeds expectation to a greater extent than i n any of the other interactions. The subclass means for t h i s i n t e r a c t i o n provide an estimate of the mean f a l l and subseguent spring weights i n each herd. They are shown i n f i g 4. The estimates, however, are not calculated independently of any Herd/Year i n t e r a c t i o n . But, as each winter change in weight occurs within any one year, the difference between these means i s a r e l i a b l e estimate of the mean winter change in weight i n each herd. These are shown i n table 7. In herds where there i s no s i g n i f i c a n t Herd/Year inter a c t i o n ( i . e . mean weight i s constant over years) the mean summer change in weight i s egual and opposite to that during the winter. In herds where there i s a s i g n i f i c a n t Herd/Year i n t e r a c t i o n , the fact that the summer change in weight crosses the interface between two adjacent years, re s u l t s i n a confounding of summer change i n weight with any change i n the mean weight of the herd. As most of the herds do have a variation i n mean weight over years, no true estimates of summer weight change, can therefore be obtained from t h i s analysis. The spring and f a l l weights in each herd. 1 2 3 Herd 1 Winter Weight Change(lb) i n each Herd Herd 1 +42.0 2 -35.3 3 -252.2 4 -130.8 Herd 5 -174. 1 6 -52.7 7 -96.1 8, -210.9 57 The Herd/Age in t e r a c t i o n i s s i g n i f i c a n t , but the amount of variation i t accounts for exceeds expectation less than that due to the herd/season i n t e r a c t i o n . The patterns of growth of the cows i n each herd are shown i n f i g 5. The deviation in each herd from the mean growth pattern can be summarized as follows: ( 1 = interaction deviation >201b<351b, 2 = >35<501b, 3 = <501b ) Herd 1 - two-year-old cows heavy (2), cider cows (ages 8+9) l i g h t (1) Herd 2 - younger cows (ages 2 + 3) l i g h t (2), older cows (ages 7- 10+) heavy (2) . Herd 3 - two-year-old cows heavy (2), older cows (ages 8+9) l i g h t (1). The deviation of the two-year-old cows i s such that there i s no increase in weight from two to three years of age. Herd 4 - younger cows (ages 2,4+5) heavy (1), older cows (ages 9+10+) l i g h t (3). Herd 5 - older cows (ages 8,10+) l i g h t (2). Herd 6 - the small number of records in t h i s herd (88) res u l t s in poor estimates f o r the age subclasses. The deviations are a l l large (3) and inconsistent. Herd 7 - younger cows (ages 2 + 3) l i g h t (2) , older cows (ages 8- 10+) heavy (3). Herd 8 - younger cows (ages 1 + 2) heavy (1) . Thus, the cows i n herds 1,3,5 and 6 reach t h e i r maximum weight at six years of age. Those i n herd 4 reach t h i s weight at f i v e years of age, while in herds 2 and 8 this i s delayed u n t i l eight and i n herd 7 u n t i l nine years of age. In herds 2 and 8 58 Figure 5 The growth curve in each herd. 2 • . 3 . 4 5 6 7 8 9 10+ Age (years) 59 the weight increase betweeen six and eight years of age i s 60.7 l b . and 43.1 l b . respectively, in herd 7 there i s a 93.0 l b . increase after six years of age. In certain herds the mean weight of the age subclasses decreases amongst older cows. There i s a 48.7 l b . decrease i n weight after age f i v e i n herd 4 and a 39.1 lb. decrease in weight aft e r age eight i n herd 8. In herd 5 the nine-year-old subclass estimate i s a product of a small number of records(4), the loss in weight from age six to the mean of ages eight and ten+ i s 54.9 l b . Owing to the small number of records from herd 6 a l l the estimates from this herd are a l i t t l e inconsistent. But there i s a decrease of 60.1 l b . between the weighted mean of f i v e to nine-year-old cows (13 records) and the mean of cows over nine years of age (13 records). Summer change i n weight - Analysis J The model for t h i s analysis can be f i t t e d to the summer weight change records in a l l the herds except herd 8. However, the number of records from herd 6 (33) and herd 9 (27) are considered to be i n s u f f i c i e n t to give r e l i a b l e estimates. Therefore these herds are not included in the combined analysis. Amongst the remaining herds, herd 7 i s the only herd in which male calves are raised as b u l l s . The use of records from t h i s herd would necessitate the addition of a t h i r d 'sex* subclass i n the analysis. Conseguently, the inclusion of these records from cows with b u l l calves (38 in total) would considerably decrease the balance of the data, without greatly increasing the t o t a l number of records. Therefore, they are not included i n the 60 analysis. The remaining records from t h i s herd (from thirty-two cows with heifer claves) are considered to be i n s u f f i c i e n t i n number and are also excluded from the analysis. The variances of the herds to be included in the combined analysis (herds 1 to 5) are not homogeneous. However, the magnitude of the differences between them i s not excessive when considered i n b i o l o g i c a l terms. They are, therefore, a l l included in the combined analysis. In t h i s analysis a l l the records from herds 3,4 and 5 are from 1974, those from herd 2 are from 1975 and only the records from herd 1 are from both years. Thus the estimates for the Herd and Year E f f e c t s are confounded and cannot be considered independently. However, the remaining estimates are unconfounded. The re s u l t s from analysis 2 of summer change in weight provide an unconfounded estimate of t h i s Herd E f f e c t . Since preliminary,individual herd analyses showed that the breedtype of a cow does not s i g n i f i c a n t l y a f f e c t her weight change through the summer, t h i s e f f e c t i s omitted from the model for the combined analysis. The ANOVA of the summer change i n weight records shown i s in table 8 and the least sguares estimates of means of the subclasses i n table 9. The least sguares constants from which the l a t t e r are calculated are i n appendix 1. The Age Effect i s s i g n i f i c a n t , and the means of the age subclasses are shown in f i g 6. The rate of decline in summer weight gain decreases over age and there i s thus a s i g n i f i c a n t guadratic e f f e c t amongst these values, but no l i n e a r component. Nine- and ten-year-olds have a s i g n i f i c a n t l y smaller weight TJBLE 8 Analysis of Variance Summer Change in Height for Two Years T Source j Herd | 1 644 I 23.14* | 0.031 I Year | 1 1 4724 I 153.51* j 0.051 1 Age j 3 1 195 I 7.02* | 0.019 I Sex of Calf | 1 } 38 ! 1.37 | 0.00 0 [ Herd x Sex j 4 I 31 I 1.13 | 0.001 Herd x Age | 29 | 31 ! 1.10 | 0.01 1 Year x Age l 8 ] 48 I 1.72 | 0.005 Year x Sex | 8 f 10 1 0.3 7 J 0.001 Prev Ch Wt | 9 I 710 1 25.50* | 0.076 Calf Age | 1 | 23 1 0.84 j 0.000 Weaning Wt j 1 I 34 1 1.25 J 0.000 Residual | 465 | 27 j ! 0. 154 F-value • i 1 R-sguare +-(* - effect s i g n i f i c a n t ) Total S.S. = 84324 Reduction S.S.= 71376 R-sguare = 0,846 % of Total S.S. assigned to parameters = 19.4 Mean value of coyaria.fal.es Previous Change i n Weighted) for Age 2 = 0 . 3 4 ± 1 1 . 7 3 3 = - 1 . 6 1 ± 9. 05 4 = - 3 . 0 2 ± 1 0 . 13 5 = - 1 . 7 3 ± 1 1 . 0 6 6 = - 5 . 0 2 ± 1 0 . 3 2 7 = - 5 . 5 2 ± 1 1 . 85 8 = - 2 . 6 9 ± 1 4 . 7 6 9 = -1.82±13.90 10+= - 1 . 7 5 ± 1 2 . 7 1 Calf Age = 213±3 3 days Weaning Weight = 430. 0.±74.3 lbs J U L E Least .Squares for Summer Change in subclass L A S A ' estimate Herd 1 7.08 (200)* 2 14.99 (155) 3 10.26 (101) 4 1.79 (3 8) 5 2. 20 (46) Year 1 12. 94 (290) 2 1.59 (250) (1) Steer c a l f 7.65 (278) (2) Heifer c a l f 6.87 (267) Herd x Age Herd 1 2 Age 2 17.98 3 10.97 20.80 4 10.19 15.69 5 2.79 10.37 6 10.54 14.09 7 6.07 12.51 8 4.56 12.30 9 3.94 15.45 10+ 2.44 12.45 Age x Year Estimates Weight for Two Years subclass L ^ S i estimate Age 2 13. 50 (50) 3 12. 38 (94) 4 9. 07 (77) 5 6. 96 (44) 6 6. 56 (57) 7 . 6. 95 (49) 8 4. 90 (41) 9 2. 01 (52) 10 + 3. 05 (76) 3 4 5 12. 17 8. 10 15.21 5.47 9. 45 9.84 5.09 4. 55 13.39 6. 28 6. 48 0.18 1. 49 10.69 2.48 2. 98 7.22 1.90 1. 48 3.98 -9.04 4. 30 7.10 5.38 -1. 39 Year 1 2 Age 2 17.10 9.90 3 17.30 7.45 4 13.48 4.66 5 11.07 2.86 6 '14.49 -1.37 7 1 1.73 2. 16 8 11.39 -1.59 9 10.04 -6,03 10+ 9.85 -3.76 (* ^ number of observations shown i n parentheses) TABLE 9 cent Herd x Sex Sex 1 2 Herd 1 7.30 6.85 2 14.67 15.31 3 10.81 9.71 4 3.62 -0.04 5 1.86 2.54 Acje x Sex Sex 1 2 Age 2 14.11 12.89 3 13.05 11.71 4 9.27 8. 87 5 7.42 6.50 6 7.47 5.64 7 6.68 7.21 8 5.75 4.06 9 1.5 0 2.52 10+ 3.64 2.45 R e g r e s s i o n c o e f f i c i e n t s f o r c o v a r i a p l e s Previous Change i n Weight for Age 2 -0.7656±0. 0037 3 — -0.6498±0. 0135 4 = -0.9436±0. 0177 5 -0.5133±0. 0046 6 -0.6638±0. 0084 7 — -0. 5638±0. 0065 8 •= -0.7278±0. 00 50 9 — -0.7732±0. 0104 10+ -0.5289+0.0101 Weaning Weight = -0. 0056±0.0050 Calf Age = -0.0086±0.0094 The summer weight change i n each age subclass. 2 3 4 5 6 7 8 9 10+ Age (years) 65 increase than cows aged four to eight. Two- and three-year-old cows have s i g n i f i c a n t l y larger increases i n weight than these intermediate aged cows. There i s no difference between the summer increase in weight of nine- and ten-year-old cows; nor between that of two- and three-year-old cows. None of the interaction subclasses in t h i s analysis are s i g n i f i c a n t b i o l o g i c a l l y or s t a t i s t i c a l l y . The effect of a cow's previous change i n weight (through the winter) has the highest R-sguare value of a l l the f i t t e d e f f e c t s i n t h i s analysis. The regression c o e f f i c i e n t for each age subclass i s s i g n i f i c a n t and t h e i r values are shown in table 9. There i s no trend across ages i n the deviation of each c o e f f i c i e n t from the o v e r a l l mean of (-0.6811 ±0.1380). The e f f e c t s associated with the c a l f a cow suckles through t h i s period (calf sex, c a l f age, c a l f weaning weight) are far removed from s t a t i s t i c a l or b i o l o g i c a l significance. Summer change in weight - Analysis 2 The model for t h i s analysis does not include the previous change in weight covariable. The reason for i t s omission w i l l be discussed i n the following chapter. This analysis was carried out i n order to obtain a non-confounded estimate of the Herd Ef f e c t . Thus only weight records from 1974 were included and t h i s necessitated the exclusion of herds 2 and 9. Although t h i s model could be f i t t e d to weight records from the other seven herds, 6 and 7 are not included i n the combined analysis. The ra t i o n a l e for t h i s decision and the omission of the Breedtype Effe c t from the model i s the same as for analysis 1. 66 The variances of the remaining f i v e herds are homogeneous and their weight records are combined in the ANOVA shown in table 10. The lea s t squares estimates of the means of the subclasses in t h i s analysis are shown i n table 11, and the least sguares constants from which they are calculated are i n appendix 1. The Herd Eff e c t i n t h i s analysis i s a very large source of variance. The least sguares estimates for each herd are shown in f i g 7. Herd 1 has a s i g n i f i c a n t l y smaller weight gain than the other range herds (3,4 and 8) and the pasture herd (5) has a s i g n i f i c a n t l y smaller weight gain than the range herds, regardless of whether herd 1 i s included or not. The age e f f e c t i s s i g n i f i c a n t and has a s i g n i f i c a n t l i n e a r pattern. The guadratic e f f e c t i s not s i g n i f i c a n t . The age/herd int e r a c t i o n i s s i g n i f i c a n t , has a r e l a t i v e l y large E-sguare value, but, due to the large number of degrees of freedom, has only an F-value of 1.7. The deviations for t h i s i n t e r a c t i o n show no trend and they can only be attributed to the r e l a t i v e l y small number of records in some of the subclasses «10) . The other interactions and the ef f e c t s associated with the ca l f a cow suckles through t h i s period are far removed from s t a t i s t i c a l or b i o l o g i c a l s i g n i f i c a n c e . Sinter change i n weight The model for t h i s analysis can be f i t t e d only to the winter change i n weight records from herds 1,2,6 and 7. Herd 6 i s excluded from the combined analysis as the number of records TABLE JO i J S ^ l j s l s of Variance for Summer Change In Weight i n 1974 Source *, + d.f. Mean Sguare ^ Herd | 4 | 4296 Age j 8 | 303 Sex of Calf | 1 I 2 Herd x Sex | 4 | 36 Herd x Age | 32 | 80 Age x Sex \ 8 | 47 Calf Age j 1 | 47 Weaning Wt | 1 I o Residual ) 36 5 I 45 , ? . . j . (* = effect F-value 95.27* 6.73* 0. 05 0. 79 1.78* 1. 04 1. 04 0.00 R-sguare .j 0.321 0.045 0.000 0.002 0.04 7 0.007 0.001 0.000 0.308 Total S.S. =53522 Reduction S.S.=37061 R-sguare = 0.692 % Of Total S.S. assigned to parameters = 42.5 Mean value of covariables Calf Age = 22 2±31 days leaning Weight = 479.2±84.5 lbs 68 TABLE 11 subclass Least Sguares Estimates for Summer Change L.S. estimate ifi Weight i n 1974 subclass L.S. estimate Herd 1 5. 02 (104)* Age 2 18. 12 (78) 3 29.47 (102) 3 19. 20 (5 3) 4 9,35 (93) 4 16, 74 (41) 5 11.67 (50) 5 12. 63 (5 9) 8 17.99 (7 5) 6 16. 79 (4 0) 7 14. 14 (42) 8 14. 44 (36) 1) Steer ca l f 14.79 (208) 9 10. 01 (37) 2) Heifer c a l f 14.61 (217) 10+ 10. 23 (39) Herd x Age Herd 1 3 4 5 8 Age 2 8.62 31.21 10. 09 15. 29 25,39 3 12.15 35.3 14.23 13. 66 20.66 4 4. 94 36.60 11. 86 15. 35 14.96 5 0.97 26.66 6. 92 13.49 15. 12 6 15.06 27.64 9.78 15. 69 15.79 7 3.93 24.55 7. 14 10. 97 24. 11 8 0. 11 29.47 13. 61 10. 63 18.61 9 0.46 29. 39 1.25 4. 38 15.49 10 + 0.09 21.05 0.48 17. 75 1 1.78 Herd x Sex Herd 1 3 4 5 8 Sex 1 6. 10 29.82 9.73 11. 14 17. 16 2 3. 94 29. 12 8. 97 12. 21 18. 82 Age •. x sex Sex 1 2 Age 2 17.35 18.89 3 20. 24 18. 16 4 15.39 .18.09 5 13.70 11.56 6 18.61 14.97 7 13.83 14. 45 8 15.23 13.65 9 7. 99 12.03 10 + 10.74 9.73 (* =number of observations shown i n parentheses) JABLE J l COIlt 2e3£§£§ion c o e f f i c i e n t s f o r c c v a r i a b l e s Weaning Weight = -0. 000 1 + 0.CC74 C a l f Age = -0.0210±0.0205 70 Figure 7 The summer weight change i n each herd. 70a 5 range herd pasture herd 30 20 (D CD « 10 U U) E E ZS (/) Herd 71 ( 2 1 ) i s considered i n s u f f i c i e n t to give r e l i a b l e estimates. Homogeneity of variance allows the records from the other three herds to be put together in a combined analysis. Herd 2 i s predominately a Hereford herd; some of the cows are Hereford/Shorthorn crosses and a few are Hereford/Angus crosses, but the exact breedtype of each i s not known. In herds 1 and 7 the cows are a l l 1 0 0 % Hereford. Therefore, breedtype i s not included in the model for the analysis. The ANOVA of these records i s shown in table 1 2 . The least squares estimates of the means of the subclasses in the analysis are in table 13 and the least squares constants from which they are calculated are in appendix 1. The Herd Effect i s a s i g n i f i c a n t source of variat i o n , but the Year and Age Effects are not. The pattern of the winter weight change amongst the age subclasses i s shown i n f i g . S. The rate of decline of winter weight change decreases with age. After the age of eiqht the pattern i s reversed and there i s a less negative winter change in weight. There i s thus a s i g n i f i c a n t quadratic ef f e c t amongst these values. The winter weight change of two-year old cows is s i g n i f i c a n t l y greater than that of cows over four years old. However, the weight change of three-year-old cows i s not s i g n i f i c a n t l y d i f f e r e n t from older or two-year-old cows. The estimates for cows over eight years old are not s i g n i f i c a n t l y d i f f e r e n t form that of four to eight-year-old cows. The mean winter changes in weight in herds 2 and 7 are negative and are s i g n i f i c a n t l y different from the winter increase in weight in herd 1. They are not, however, 72 TABLE 12 Analj s i s of Var iance for wint er Change in Weight Source | d. f, j M€ an Squarej F-valua j ft-square — _ _^— Herd j 2 I 263 | 11.57* j | 0.018 Year j 1 I 18 | 0. 80 | 0.000 Age | 8 I 44 | 1.94 I 0.0 13 Herd x Year | 2 I 7 89 | 34.74* | 0.oo7 Herd x Age | 16 I 75 | 3.28* | 0.043 Age x Year | 8 I 45 | 1. 96* i 0.013 Sp Interval | 1 I 239 | 10.51* | 0.009 Prev Ch Mt j 9 I 596 | 26.25* i 0 . 1 J 3 Residual | 54 4 23 | i j 0 . <4 4 4 mJL—~ (* = effect significant) Total S.S. = 27832 Reduction S.S.= 15483 R-square = u. 53c. % of Total S.S. assigned to parameters = 34.6 I S I S v i l u j of covariables Spring Interval = 26±14 days Previous Change in Weight (X) for Age 2 3 4 5 6 7 9 ^  10 + ; 2.95±6.98 12. 90±6.a3 7. 11±8.«44 2.36+6.01 4.25±7.o6 5.11 ±6. ci 3 -1. 94±8.j7 1.50+6.50 2.92±7.o 1 TABLE 13 l e a s t Sguares Est i m a t e s f o r Winter Change i n i s ^ h t s u b c l a s s Herd 1 2 7 Year 1 2 i z J L e s t i m a t e 1.55 (161)* -0.49 (391) -3. 02 (40) -0,60 (180) -1.35 (4 12) s u b c l a s s Age 2 3 4 5 6 7 8 9 10 + L. e s t i m a t e 2. 6 3 0. 73 -1. 71 -0. 59 -2. 04 -2. 54 -3. 12 -1. 55 -0. 58 (46) (107) (9 2) (60) (b0) (46) ( 4 3 ) (48) ( *Q) Herd x Year Herd 1 2 7 Year 1 5. 04 -5.39 -3.01 2 -1. 94 -0. 65 -3. 04 Hexa x Age Herd 1 2 7 Age 2 -2. 06 3. 38 7.51 3 3. 47 2.50 -2.81 4 4. 01 -0. 19 -7.99 5 3.55 1. 04 -5. 39 6 -0. 47 0. 27 -4. 95 7 0.57 -3.51 -3.72 8 0. 78 -3. 41 -5.76 9 1.67 -2.25 -3.1 1 10 + 2. 47 -2. 27 -0. 93 Age x Year Year 1 2 Age 2 2.54 2.71 3 1. 03 0.43 4 -0. 20 -3. 23 5 -1. 86 0. 68 6 -2. 94 -1. 14 7 -2. 47 -2. 60 8 -2. 24 - 3 . S 9 9 -0. 56 -2. 54 10 + 1.33 -2.49 =number of o b s e r v a t i o n s shown i n parentheses) Previous Change i n Weight for Age 2 = -0.4020±0.1432 3 -= -0. 4367±0.0732 4 = -0.4756+0.U702 5 - -0. 5257±0. 1u86 6 = -0.5314±0.0b54 7 - -0.4956±0.1121 8 = -0.6495±0.0*69 9 = -0. 6360±U. 13 19 10+= -0.5216±0.0735 Spring i n t e r v a l = -0,0650±0.0200 75 F i g u r e 8 The winter weight change in each age subxass 76 s i g n i f i c a n t l y different from each other. The two interactions which include the Herd Effect are s i g n i f i c a n t and have r e l a t i v e l y high Revalues. The least squares estimates for each interaction subclass are shown in f i g s . 9 and 10. From these i t can be seer, that these e f f e c t s are b i o l o g i c a l l y s i g n i f i c a n t . They w i l l be discussed in the following chapter. The Age x Year interaction i s s t a t i s t i c a l l y s i g n i f i c a n t , but i t s b i o l o g i c a l s i g n i f i c a n c e i s r e l a t i v e l y small. Only two of the interaction sublcass constants have values which are greater than 1,5% (approximately 15 l b . ) . The Spring Interval Effect i s s i g n i f i c a n t , but i t s b i o l o g i c a l significance is also r e l a t i v e l y small. The cows i n i t i a l l y lose weight post-partum. The weight loss i s 0.07$ (0.7 lb.) per day. The o v e r a l l Previous Change in Weight Effect i s s i g n i f i c a n t and has the highest R 2-value of a l l the f i t t e d e f f e c ts in t h i s analysis. The values of the regression c o e f f i c i e n t s for the Previous Change in Weight Effect vary across ages, with a tendancy for those of older cows (aqes 8-10, mean b = -0.6024) to be greater than those f c r younqer cows (ages 2-4, mean b = -0.4381). The effect of t h i s covariable i s s i g n i f i c a n t in a l l the age subclasses except age twc. Table 10 shows the considerable differences which exist between the mean value of the previous change in weight in each age subclass. Winter analysis in Herd 2± The A NOVA of the f a l l , January and February weight records from herd 2 i s shown in table 14. The least sguares estimates of winter weight change in each herd/age subclass. Winter Weight Change (%) LO - W -I 1 i i i r kXWUWWW LO U I W W \ \ \ \ \ k\\\\\\\V\\\\\\\\\\\\\V I X X X Q O 0) rv> \j ft*\\\vt\\\\\\\\\\\\\\i oo I I ID %\\\\W\\\\\\\\> r m w w w w w w v o > CO 0) 0) 1 cn 78 Figure JO The winter weight change i n each herd/year subclass. Winter Weight Change (%) *8L 79 the means of the s u b c l a s s e s i n the a n a l y s i s are i n t a b l e 15 and the l e a s t squares co n s t a n t s from which they were c a l c u l a t e d are i n appendix 1. A major source of variance i n the data i s the Aqe E f f e c t . The Year E f f e c t i s a l s o s i g n i f i c a n t s t a t i s t i c a l l y , but the S 2 - v a l u s a s s o c i a t e d with i t i s r e l a t i v e l y s m a l l . The i n t e r a c t i o n between these e f f e c t s i s s t a t i s t i c a l l y s i g n i f i c a n t but i t s b i o l o g i c a l s i g n i f i c a n c e , i s n e g l i g a b l e - only t h r e e age/year s u b c l a s s e s have an i n t e r a c t i o n d e v i a t i o n of more than 10 l b . The r e g r e s s i o n c o e f f i c i e n t s f o r days pregnant (DP), DP 2, DP 3 are a l s o shown i n t a b l e 15. The a n a l y s i s which i n c l u d e d a l l three c o v a r i a b l e s together had a s i g n i f i c a n t l y l a r g e r r e d u c t i o n S.S. than those with DP + DP 2 or DP alone. The combined e f f e c t of the c o v a r i a b l e s was s i g n i f i c a n t s t a t i s t i c a l l y and b i o l o g i c a l l y (R 2 = 0.076). Each c o v a r i a b l e was a l s o independently s i g n i f i c a n t . The r e d u c t i o n S.S. was not i n c r e a s e d s i g n i f i c a n t l y by f i t t i n g these three c o v a r i a b l e s independently w i t h i n each age s u b c l a s s , t h e i r e f f e c t d i d not, t h e r e f o r e , vary between ages. The e f f e c t of these c o v a r i a b l e s on cow weight i n the range of DP i n c l u d e d i n the data (90 to 285 days) i s shown i n f i g 11. From a mean weight of 1004.2 l b . at 90 days pregnant, the weight of a cow i n i t i a l l y i n c r e a s e s r a p i d l y . The r a t e of i n c r e a s e then peaks at a mean of 1105.6 l b . at 260 days pregnant. There i s then a s l i g h t decrease i n weight, so at 285 days pregnant, the day on which p a r t u r i t i o n i s assumed to occur, the mean weight i s 1098.8 l b . This i s an i n c r e a s e of 94.6 l b . during the l a s t t wo-thirds of pregnancy. This weight change and that o c c u r r i n g immediately post-partum are d i s c u s s e d i n the 80 TABLE 14 Analysis of Variance for Winter Weights frog. 2. j Source | d. f. |Mean SguareJ F-value | R-sguare 1 ' i t 1 J Year 1 1 J 720390 | 102.71* 1 0.022 1 Age | 10 | 1182420 } 168.59* | 0.355 j Year x Age I 9 | 17381 | 2.48* | 0.005 j Days Preg i 3 | 839228 | 119.66* | 0.076 J Residual | 1946 | 7014 | j 0.410 | _ ,i i i _ j... _ (* = eff e c t s i g n i f i c a n t ) Total S.S. -= 0.333245E+8 Reduction S.S.= 0.196762E+8 R-sguare -= 0.590 % of Total 5.3. assigned to parameters = 45.7 Mean value of covariables Days pregnant = 194 (Days pregnant) 2 = 40298 (Days pregnant)^ - 8812268 S-s-guare 0. 001 0. 002 0. 003 81 TABLE 15 Least Squares Estimates f o r winter An.lv.sis For a§.rd 2 subcla s s L i S i estimate Age 2 841. 3 (160) * Age 3 3 967.5 (444) 3 1032.0 (240) 4 5 1060.0 (165) 4 o 1064.9 (220) 5 7 1087.9 (130) 5 8 1150.6 (124) 6 9 1117.4 (126) 6 10 1123.8 (118) 7 11 1137.8 (89) 7 12 + 1134.5 (154) 8 Year 1 2 1039.4 (1055) 1091.3 (915) su b c l a s s x Year 8 9 9 10 10 11 11 12 + 12 + Regression c o e f f i c i e n t s for. c o v a r i a b l e s Days pregnant = -3.127±1.210 (Days p r e g n a n t ) 2 = 0.02267±0.00678 (Days p r e g n a n t ) 3 = -0.424E-4±0,122E-4 i i ^ s . " e s t i m a t e 1 944.7 2 990.3 1 1002.9 2 1U61.2 1 1051.3 2 1070.2 1 1033.1 2 1096.8 1 1U60.5 2 1115.3 1 1123.6 2 1177.7 1 1061.7 2 1173.0 1 1108.8 2 1138.8 1 1106.6 2 1141.0 1 1110.5 2 1158.5 (* =number of o b s e r v a t i o n s shown i n parentheses) Figure changes i n weight and p a r t u r i t i o n 11 through pregnan i n herd 2 . o u 9 6 0 r 120 160 Days Pregnant 200 240 2 8 0 8 3 following chapter in r e l a t i o n to the r e s u l t s of the ether analyses. 84 Chapter 6 Discussion This discussion i s divided into three sections. I n i t i a l l y the r e s u l t s are discussed in r e l a t i o n to i) the a n a l y t i c a l procedures used, i i ) the i n t e r - r e l a t i o n s h i p between the analyses, i i i ) the variance which can be explained by the management practices of the operations. This i s then followed by a discussion of the influence of the parameters per se on cow weight and weight change. The chapter i s terminated by a discussion of the s a l i e n t points from t h i s research. Section 1. - Discussion of the Analyses weight analysis The model for t h i s analysis accounts for 61.8% of the t o t a l variance in the weight records. The following factors w i l l be included in the remaining error variance: 1) The varying i n t e r v a l from calving to weighing. As mentioned i n chapter 5, the e f f e c t of t h i s was minimized by excluding records with an excessively long i n t e r v a l . 2) The s l i g h t l y d i f f e r e n t set of cows which were weighed on consecutive occasions. 3) The inclusion of some non-pregnant cows from herd 2. 4) Any variation between animals i n t h e i r a b i l i t y to obtain feed. This i s l i k e l y to be of greatest s i g n i f i c a n c e in the winter and i s discussed in r e l a t i o n to the weight change in t h i s period. 85 5) The other parameters mentioned i n Chapter 5 which were not included i n the model, e.g. genotype. 6) Any variation i n the weight of stomach contents at weighing. 7) Any errors in weighing. However, only of the t o t a l S.S. was assigned to s p e c i f i c e f f e c t s . This l i m i t a t i o n in p a r t i t i o n i n g the reduction S.S. i s due to the imbalance of the data and the lack of orthogonality amongst the f i t t e d e f f e c t s . Nevertheless, certain parameters are s i g n i f i c a n t . Herd The mean weight of a herd w i l l be dependent on the following two factors and their i n t e r a c t i o n : 1) The genotype (s) of the cows i n the herd - a result of the breeding management, conscious or otherwise, of the herd operators. 2) The environmental parameters influencing the herd, e.g. a v a i l a b i l i t y of nutrients, climate. Thus, the winter feed management i n herd 1 i s known to be l i b e r a l (see l a t e r ) ; the cows i n th i s herd were the only ones i n th i s study to gain weight overwinter. This above average l e v e l of winter feeding i s at least part of the reason why the mean weight of t h i s herd i s s i g n i f i c a n t l y heavier than that of the crossbred range herds. In contrast, the sub-optimal winter feeding in herd 3 (see later) causes the cows in t h i s herd to be r e l a t i v e l y l i g h t and have very large seasonal changes i n weight. Joandet and Cartwright (1969) and Fitzhugh et a l . (1967) assumed that the si m i l a r , but smaller, seasonal variation which they observed, 86 was occurring around the expected or 'true mean weight* of each cow. However, in the present research t h i s assumption does not hold for herd 3. The extremely poor winter feeding i n t h i s herd res u l t s i n an excessive winter weight loss (252.1 lb.) and the occasional death of cows. Each summer a cow has to regain t h i s large winter weight l o s s , as well as nursing a c a l f . Consequently, she only reaches a weight close to her 'true mean weight' before she i s exposed to another winter of extremely poor n u t r i t i o n . Her mean weight i s , therefore, less than that which would be expected with an average winter nutrient supply. If the 'true mean weight* of the cows in t h i s herd were assumed to be closer to the upper l i m i t of the i r seasonal variation (around 991 l b . ) , t h e i r mean weight would be s i m i l a r to the weighted mean of the cows i n the other range herds i n t h i s study (971.5 l b . ) . The information available about the management practices and summer grazing g u a l i t y suggests that the mean weights of the cows in the other seven herds are close to t h e i r 'true mean weights*. This subjective assessment i s considered to be true even for herd 8. The large seasonal change in weight in t h i s herd (210.9 lb.) i s more l i k e l y to be a product of the cows getting f a t during the summer on good quality range than a product of poor winter n u t r i t i o n . The other herd ccmparisions, from which herd 3 was omitted, are discussed i n section 2. Herd x Age Although the cows i n herds 1, 3, 5 and 6 reach their maximum weight at six years of age, those i n herds 2, 7 and 8 87 continue to increase in weight after t h i s age, while the cows in herd 5 dc not increase i n weight after the age of f i v e . There are also other between herd differences i n the pattern of growth in early l i f e . This variation could be due to genetic and/or environmental factors. For example, genetic differences in the rate of maturing are known to cause variations in the pattern of growth (Fitzhugh and Taylor, 1971; Brown et a l . , 1972), A l t e r n a t i v e l y , the c l a s s i c a l experiments of McMeekan (1940) show that the growth pattern of pigs can be influenced environmentally through the a v a i l a b i l i t y of feed. In the present research i t i s impossible to separate objectively such genetic and environmental influences. However, the feeding management i n each herd i s known to d i f f e r considerably and i t can be speculated that t h i s i s a major reason for the between herd difference in growth patterns. A s i m i l a r conclusion can be made about the weight loss which occurs i n the older cows in four of the herds. Although three of these herds (4, 5 and 8) are crossbred herds, there appears to be no reason why this genetic factor per se should account for the weight loss. Herd x Season The proportion of the variance accounted f o r by t h i s i n t e r a c t i o n e f f e c t i s considerably greater than that accounted for by any of the other interactions i n the ANOVA. The reason why the mean summer weight changes i n a herd cannot be calculated from the season subclass means f o r that herd was mentioned in the previous chapter. 88 The estimates of winter weight change, however, suffer from the l i m i t a t i o n that the weight records included for a herd each f a l l and spring do not come from exactly the same set of cows. However, the estimates from the i n d i v i d u a l herd analyses for winter change in weight are calculated from the weight changes of i n d i v i d u a l animals, i . e . the same set of cows each f a l l and spring. On comparing these two sets cf estimates of winter weight change, i t i s apparent that the l i m i t a t i o n of the present analysis affects only the estimate from herd 5. Only one set of spring weight records was obtained from t h i s herd and considerable c u l l i n g was carried out during the course of t h i s study. Consequently the winter weight loss (-174.1 lb.) estimate from the analysis i s double the estimate of the weiqht loss of i n d i v i d u a l cows (approximately -85 l b . ) . This spurious result w i l l not, therefore, be included i n the discussion which follows. The winter weight change estimates from the other herds r e f l e c t the weiqht chanqes of individual ccws. These weiqht changes are the r e s u l t of a number of i n t e r - r e l a t e d factors. These w i l l be discussed f u l l y i n r e l a t i o n to the analysis of winter change in weight l a t e r in the discussion. However, the main determinant of a cow's winter weight change i s the winter feed management i n the herd. The information which the author has been able to c o l l e c t about winter feed management i s known to suffer from the following l i m i t a t i o n s : 1) Any estimate of the amount fed i s r e l a t i v e l y subjective. 2) It lacks an assessment of feed guality. 89 It i s , however, considered to be useful and s u f f i c i e n t to aid the discussion of the winter weight changes recorded in t h i s study. Winter feeding i n a l l the herds i s based on conserved forage, and the amount available to the cows during the winter i s controlled e n t i r e l y by each operator. It i s , therefore, not surprising that there i s a cor r e l a t i o n between the winter weight changes of the cows and the different management p o l i c i e s of these individuals. The only cows which gain weight over the winter are those in herd 1. after returning from summer range, around the beginning cf November, these animals are allowed to graze on some rough ground and adjacent hay meadows. 20-25 l b . of grass hay i s normally fed per cow per day froa mid- or l a t e December u n t i l the f i r s t or second week i n February. It i s then replaced by 20 l b . a l f a l f a hay and 8-10 l b . corn s i l a g e and feeding i s continued u n t i l the cows are turned out on summer range, normally in mid-April. This herd i s owned by the pr o v i n c i a l government and i f i s possible that factors other than commercial p r o f i t are included i n the management objectives. Consequently, the winter feeding i s r e l a t i v e l y l i b e r a l and the cows gain weight (+42.0 l b . ) . The winter feed management in t h i s herd i s described i n some d e t a i l because the rather a t y p i c a l weight changes of the cows in thi s herd w i l l be considered on several subsequent occasions in t h i s discussion. The smallest winter weiqht loss (-35.3 lb.) occurs i n herd 2. The winter feedinq i n th i s herd i s aqain r e l a t i v e l y l i b e r a l , approximately 10 l b . of hay and 35-45 l b . of s i l a q e are fed 90 per cow per day. A s i m i l a r weiqht l o s s (-52.8 lb.) occurs i n herd 6, a s m a l l herd of purebred Aberdeen Anqus cows. Aqain winter feed manaqement i s r e l a t i v e l y l i b e r a l , 20-25 l b . of gras s hay i s fed per cow per day and t h i s i s supplemented with a n a d - l i b i t u m supply of corn s i l a g e from mid-February onwards. The other herd which has a weight l o s s t h a t i s l e s s than the mean i s herd 7. T h i s i s a r e l a t i v e l y s m a l l herd of r e g i s t e r e d Hereford cows i n which the winter f e e d i n g p o l i c y i s to provide as much grass hay as the cows w i l l c l e a n up. The r e s u l t of t h i s management, combined with a winter c l i m a t e which i s more severe than t h a t f o r the three p r e v i o u s l y mentioned herds, i s a 96.1 l b . l o s s i n weight over winter. The winter weight change estimate of the remaining pasture herd, herd 5, has been p r e v i o u s l y d i s c u s s e d and i s c o n s i d e r e d to be s p u r i o u s . There i s some i n d i c a t i o n that the winter weight l o s s i s s i m i l a r to t h a t of herd 7. T h i s r e l a t i v e l y s m a l l winter weight l o s s i n herd 5 i s the product of winter f e e d i n g based on equal g u a n t i t i e s of corn s i l a g e and grass hay. The winter feed management i n herd 8 i s to feed 20-25 l b . of a l f a l f a hay per cow per day. T h i s i s supplemented with a l i m i t e d amount of p r o p r i e t a r y concentrate feed or a l f a l f a cubes post-partum. In the summer the cows are on good q u a l i t y summer range and r e t u r n i n the f a l l i n e x c e l l e n t c o n d i t i o n - as r e f l e c t e d i n t h e i r heavy f a l l weights. T h e i r l a r g e winter weight l o s s (-210.9 lb.) i s thus a product of 1) winter f e e d i n g 2) an a t y p i c a l l y l a r g e n e g a t i v e compensatory weight gain - a consequence of the cows being * f a t ' i n the f a l l . T h i s l a t t e r p o i n t w i l l be d i s c u s s e d i n more d e t a i l i n r e l a t i o n to the change 9 1 in weight analyses. In herd 4 winter feeding i s s i m i l a r to that i n herd 8, without the supplementation post-partum. However, the weight loss in t h i s herd (-130.8 lb.) i s considerably less that that in herd 8. It appears that this difference i s due to a smaller negative compensatory gain component in the winter weight loss in herd 4. The excessive winter weight loss i n herd 3 (-252.1 lb.) has already been mentioned. The winter feed management i n t h i s herd i s based e n t i r e l y on grass and a l f a l f a hay. The g u a l i t y of the hay i s known to be variable and quantity fed meagre, hence the large l o s s in weight and occasional death of cows previously mentioned. Summer change in weight - Analysis J The reduction S.S. i n t h i s analysis accounts for 84.7% of the t o t a l variance in the summer change in weight records. With the exception that weight records froa an i d e n t i c a l set of cows are included i n a spring and in the subsequent f a l l , a l l the other factors mentioned as being sources of error i n the absolute weight analysis are included i n the present error variance. In addition, the cows i n three of the herds were not a l l weighed on the same occasion in a f a l l or spring. Although t h i s reduces the length of the Spring Interval, i t r e s u l t s in a variation i n the length of the summer periods within these herds. This w i l l , therefore, be an additional component of the error variance. The imbalance of the data and the lack of orthogonality 92 amongst the f i t t e d e f f e c t s allows only 19.4% of the t o t a l S.S. to be s p e c i f i c a l l y assigned i n the ANOVA despite t h i s l i m i t a t i o n , certain of the parameters in the model are s i g n i f i c a n t . Previous change i n weight The largest source of variation in the summer gain in weight i s the e f f e c t of the change in weight of the cows i n the previous winter. The regression c o e f f i c i e n t f or each of these covariables i s negative and s i g n i f i c a n t . The e f f e c t of th e i r inclusion i n the analysis i s to remove the variation in summer weight gain that i s caused by the deviation of a cow's winter weight change from the mean of i t s age subclass. This allows the fixed e f f e c t s which are included in the model to be estimated with greater precision. The b i o l o g i c a l i nterpretation of thi s 'covariable c o r r e c t i o n 1 i s as follows. A cow whose winter weight loss i s greater than the mean for her age subclass w i l l enter the summer period i n r e l a t i v e l y poor condition. Conseguently, her summer weight gain w i l l contain a positive compensatory gain component which i s greater than that of a cow of the same age which has a mean winter weight loss. The inclusion of the covariable corrects f o r , i . e . removes, t h i s extra weight gain. Conversely, a cow which loses l e s s weight than the mean w i l l be r e l a t i v e l y f a t and w i l l have a smaller positive compensatory gain. If she gains weight through the winter her compensatory growth in the summer w i l l be negative. The covariable in these cases adds a compensatory growth component to a summer weight change record to make t h i s 93 component of the weight change equal in a l l the records in the analysis. The value of the regression c o e f f i c i e n t s f o r previous change in weight varies between -0.5133 (five-year-old subclass) and -0.9435 (four-year-old subclass), but there i s no trend around the mean value of -0.6811. The variation which i s present i s due to non-random sampling variation and/or the l i m i t a t i o n of the s t a t i s t i c a l analysis i n ca l c u l a t i n g an estimate of the effe c t from amongst a l l the variance present in the data. This l a t t e r l i m i t a t i o n could be re f l e c t e d in each subclass estimate for summer weight change. If i t i s present, i t would be most s i g n i f i c a n t i n the herd subclass means, which have the largest previous change in weight deviations. In the ether subclasses the sum of the deviations i s either zero (age), or the e f f e c t s are far removed from s i g n i f i c a n c e . The importance of t h i s l i m i t a t i o n i s thus minimal i n these subclasses. This possible spurious influence on the herd estimates was the reason for omitting the Previous Change in Weight Effect from the model for analysis 2 of the summer weight change records. In the present analysis the confounding of the Herd and Year Effects also precludes any meaningful comparisons amongst the herd and year estimates. Therefore, the Year E f f e c t was also removed from the model for analysis 2. The estimates for t h i s analysis are s i m i l a r to the summer change i n weight estimates from the absolute weight analysis, i . e . younger cows have s i g n i f i c a n t l y greater weight gains than older cows. The present estimates, however, have a s i g n i f i c a n t 94 quadratic trend over age, while those from the absolute weight analysis appear to have a more linear pattern. This difference i s a product of the smaller sample of records included i n t h i s analysis. Sumner change in weiqht - Analysis 2 The B-square value for the reduction S.S. in t h i s analysis (0.692) i s 15.0% l e s s than that in anlaysis 1. This difference i s j o i n t l y due to the lack of the previous change in weight parameter and the d i f f e r e n t records included in each analysis. The variation due to the previous change i n weight of the cow i s now present i n the error variance, together with a l l the ether factors mentioned previously. The records i n thi s analysis are considerably more balanced than those i n analysis 1 of summer weight change and consequently the proportion of the t o t a l S.S. s p e c i f i c a l l y assigned to eff e c t s in the ANOVA has increased to 42.52*. Herd The mean summer change in weight estimates for each herd in t h i s analysis are not confounded and are not influenced by the previous change in weight covariable. Even though the estimates are from enly one summer (1974), they are s i m i l a r i n magnitude, but opposite i n sign, to the winter weight loss estimates for these herds from the absolute weight analysis. The exceptions to th i s are herds 1 and 5. The magnitude of the estimate for herd 5 i s further evidence to indicate the previously mentioned winter weight loss anomaly for thi s herd. The estimate for herd 1 w i l l be discussed l a t e r in t h i s section of the discussion. 95 Each herd mean contains both a compensatory gain and a 'new weight gain* component. It i s , however, impossible to separate them quantitatively. It would appear, however, that although the summer weight gain must r e f l e c t the productivity of the summer grazing for each herd, the influence of the human controlled winter weight loss i s a major factor determining i t s magnitude. Hence, as a conseguence of l i b e r a l winter feeding, herd 1 has a small summer weight gain, while poor winter feeding in herd 3 re s u l t s i n a very large summer weight gain. Consequently the large amount of variation accounted for by t h i s herd e f f e c t (R-square = 0.321) i s very much a product of the d i f f e r i n g winter management p o l i c i e s of the herd operators. In the absolute weight analysis the pasture herds were found to be heavier than the range herds. I t i s apparent from t h i s analysis that the heavy cows in herd 5 {which was the heaviest of the pasture herds) do not put on more weight in the summer than the cows in the range herds. The reason for the heavier cows i n t h i s herd, and probably i n the other pasture herds as well, i s therefore to do with the a v a i l a b i l i t y of nutrients in"both summer and winter. The cows are fed at an above average l e v e l i n the winter, thus a greater proportion of the summer weight increase i s 'new weight gain* and the cows are r e l a t i v e l y heavy. The large summer weight gain of three-year-old cows and the li n e a r decline i n weight gain over age which were apparent in the absolute weight analysis are also present i n t h i s analysis. The difference between these estimates and those of analysis 1 9 6 i s a product of the d i f f e r e n t records i n c l u d e d i n each a n a l y s i s . Winter change i n weight a n a l y s i s The r e d u c t i o n S.S. i n t h i s a n a l y s i s accounts f o r 55.6% of the t o t a l v a r i a t i o n i n the winter change i n weight r e c o r d s . Of the f a c t o r s mentioned i n r e l a t i o n t o the e r r o r v a r i a n c e o f the summer change i n weight a n a l y s i s 1, the v a r y i n g i n t e r v a l from c a l v i n g t o weighing i s the onl y one not i n c l u d e d i n the present e r r o r v a r i a n c e . T h i s S p r i n g I n t e r v a l E f f e c t i s i n c l u d e d as an independent v a r i a b l e i n the a n a l y s i s . I t can be s p e c u l a t e d t h a t the r e l a t i v e l y l a r g e e r r o r v a r i a n c e i n t h i s a n a l y s i s i s a s s o c i a t e d with the v a r y i n g a b i l i t y of cows t o compete f o r the l i m i t e d amount of winter feed. The more ag g r e s s i v e cows o b t a i n a b e t t e r g u a l i t y and g u a n t i t y of winter feed and consequently have s m a l l e r weight l o s s e s (or gr e a t e r weight g a i n s ) . Owing to the r e l a t i v e l y balanced data f o r winter weight change, a l a r g e p r o p o r t i o n (62.2%) of the r e d u c t i o n S.S. i s s p e c i f i c a l l y a s s i g n e d t o parameters i n the ANOVA, i . e . 34.6% of the t o t a l S.S. The p o s s i b l e i n a d e g u a c i e s of a c o v a r i a b l e c o r r e c t i o n were di s c u s s e d i n r e l a t i o n to the summer change i n weight a n a l y s i s 1. The winter weight change estimates might a l s o be a f f e c t e d by t h i s l i m i t a t i o n . However, owing t o the very much s m a l l e r magnitude of the d e v i a t i o n s of the previous weight change i n each herd (maximum d e v i a t i o n from the mean = 2.9%) and the small i n f l u e n c e of the s p r i n g i n t e r v a l d e v i a t i o n s (b=-0.0650) any such l i m i t a t i o n i n t h i s a n a l y s i s i s l i k e l y t o be s m a l l . Conseguently, 97 a discussion of a l l the effects can be based on the estimates which were reported i n chapter 6. Previous change in weight The change in weight of the cow i n the previous summer has a major influence on her winter weight change. The e f f e c t of the inclu s i o n of t h i s covariable i s exactly the same as in the summer change i n weight analysis 1. It removes the variation in winter weight change which i s due to the deviation of a cow's previous summer gain i n weight from the mean value for her age subclass. It thus allows the fixed e f f e c t s to be estimated with greater precision. The rationale for f i t t i n g t h i s covariable independently in each age subclass i s substantiated by the lack of s i g n i f i c a n c e of this covariable in two-year-old cows and by the large variation in the mean value for each covariable. The reason f o r t h i s non-significance of the covariable i n two-year-old cows and the trend i n the magnitude of the c o e f f i c i e n t s over age w i l l be discussed in the following section. Herd The herd estimates are expressed as a percentage of a cow's mean body weight and are corrected for the previous change i n weight. Nevertheless, they are ranked i n the same order as i n the absolute weight analysis. The difference (when expressed i n absolute terms) between these two sets of estimates i s a product of the covariable corrections and the d i f f e r e n t records included in each analysis. 98 Aje The r e l a t i v e l y l i b e r a l winter feeding in the herds included in t h i s analysis i s especially apparent in the age subclass estimates. Whereas a l l the age groups in the absolute weight analysis have eguivalent winter weight losses (mean=-88 l b . ) , the younger cows in t h i s analysis tend to gain weight and the older cows have only small weight losses. However, the difference between the age subclasses i s not s i g n i f i c a n t o v e r a l l , which confirms the conclusions made about the eguivalent absolute weight estimates. Age x Herd The guadratic pattern of weight change over age i s not the same in each herd. In herd 1 l i b e r a l feeding during rearing and extra feeding in the winter period prior to f i r s t calving results i n r e l a t i v e l y heavy two-year-old cows (see absolute weight a n a l y s i s ) . Conseguently, although most of the age subclasses in t h i s herd gain weight, two-year-old cows lose weight over winter. The other large deviation i n t h i s herd (+3.19% for four-year-old cows) i s not associated with an unusual absolute weight and lacks an apparent b i o l o g i c a l explanation. The r e l a t i v e l y small two-year-old cows in herd 7 have an a t y p i c a l l y large winter weight gain (interaction deviation = +6.93%). However, there are only two observations in t h i s subclass and the estimate i s t o t a l l y u nreliable. The other large interaction deviations, in four (-4.23%) and five-year-old cows (2.75%), are not related to unusual absolute weights and they again lack any apparent b i o l o g i c a l explanation. 99 Herd x Year Although the o v e r a l l Year Effect i n t h i s analysis i s not s i g n i f i c a n t , the winter weight changes in herds 1 and 2 do vary s i g n i f i c a n t l y between years. In herd 2 the 2.92$ (approximately 29 lb.) difference between years appears to be associated with a milder winter i n year 2, rather than any difference in winter feeding. The difference between years i s most pronounced in herd 1. In year 1 the cows gain weight (5.0435), while i n year 2 they lose weight (-1.94%) - a between year difference of approximately 71 l b . The anomalous weight changes i n t h i s herd have already been mentioned several times. They w i l l now be integrated and discussed. The weight changes in herd J , The weight changes i n t h i s herd are best discussed as absolute, uncorrected weight changes. The most comprehensive estimates of these changes are obtained from the preliminary, in d i v i d u a l herd analysis of the weight records: they are as follows. Year 1 1 2 2 3 3 Season f a l l spring f a l l spring f a l l spring Weight J l b x l 943.5 1001.6 1046.4 1090.1 1047.4 1063.6 Weight Change + 58. 1 + 44. 8 + 43. 7 -42. 7 + 16. 2 The cows in t h i s herd have a steady increase in weight 1 0 0 between the f a l l of year 1 (1973) and the sprinq of year 2 (1975). The 44.8 lb. summer weiqht qain i s smaller, but i n the same dire c t i o n as the weight chanqes i n the other herds in t h i s study. The winter weiqht qains, however, are d i s t i n c t l y d i f f e r e n t from the winter losses in a l l these other herds. It has already been mentioned that the winter weiqht change i n a herd must i n e v i t a b l y r e f l e c t the winter feeding policy of each operator. Therefore, in order to aid t h i s discussion, the winter feeding policy of herd 1 has previously been described in some d e t a i l . However, although such a subjective assessment can be made, a quantitative assessment of nutrient intake would be necessary to d e f i n i t e l y resolve the present anomaly. But, from the information a v a i l a b l e , i t appears that the winter feedinq i n t h i s herd i s l i b e r a l and could result i n a weiqht qain over t h i s period. It might be speculated from the consistent eighteen month weight increase that the cows were in r e l a t i v e l y poor condition at the outset of the study. Enguiries by the author, however, have not produced any information to substantiate t h i s . Hevetheless, the cows must have been in good condition i n the spring of year 2 and i t would have been b i o l o g i c a l l y possible for the cows to lose 42.7 l b . during the following summer. The author has been unable, however, to f i n d any management or ether environmental factor which might have brought t h i s about. The small increase in weight (+16.2 lb.) i n the winter following t h i s summer weight loss indicates the following: 1) As a d i f f e r e n t scale was used for the f a l l and spring weighings, the weights recorded on the former occasion are not 101 l i g h t merely because of an inaccuracy of the scale used. 2) Even though winter feeding was l i b e r a l there was no large positive compensatory gain. The cows were thus s t i l l in reasonable condition in the f a l l after their summer weight loss; consequently they must have been fat the previous spring. It can be concluded from these r e s u l t s that human influences are a major factor c o n t r o l l i n g the weight changes in a cow, i . e . winter feed management. However, the extent to which cow weight can be manipulated by man has b i o l o g i c a l l i m i t a t i o n s . Hence the anomalous summer weight lo s s . Winter analysis i n herd 2 The reduction S.S. in t h i s analysis accounts for 59.0% of the t o t a l variance present in the weight records. The factors included in the error variance are inevitably the same as those l i s t e d i n the absolute weight analysis. However, the effect of s o c i a l i n t e r a c t i o n during feeding, which was discussed i n r e l a t i o n to the winter change i n weight analysis, w i l l be more important as a component of error i n t h i s analysis. The proportion of the t o t a l S.S. assigned in t h i s analysis (45.7%) i s greater than that assigned i n any of the other analyses. This i s the result of the more balanced data from t h i s single herd. The s i g n i f i c a n t Year Effect i s due to the following factors: 1) The cows were brought in off range a month e a r l i e r i n year 2, and thus they entered the winter in better condition. 2) The winter in year 2 was considerably milder than that in 102 year 1. The subclass estimates for age have the same pattern as those in the absolute weight analysis, i . e . an increase i n weight up to eight years of age, and a r e l a t i v e l y stable weight after t h i s point. In f i g 11 the weight estimates from t h i s analysis are integrated with those from other analyses car r i e d out on the records from t h i s herd. The rationale for t h i s integration i s as follows. 1) The mean spring weight from the in d i v i d u a l herd analysis i s 996.6 l b . The mean spring i n t e r v a l between p a r t u r i t i o n and t h i s occasion of weighing i s 31 days and the mean weight loss i s -0.07% of a cow»s mean weight per day. The mean weight loss i s thus 22.2 lb. and mean cow weight immediately post-partum i s 1018.8 l b . 2) The f a l l weight estimate from the in d i v i d u a l herd analysis i s 1040.0 l b . Thus there i s a mean loss of 21.2 lb. Between the f a l l weight and that immediately post-parturition 3) The mean weight immediately pre-partum i s 1098.0 l b . the mean weight loss due to pa r t u r i t i o n i s 80.0 l b . or 7.3% of the pre-partum weight. Although the mean b i r t h weight of calves i n t h i s herd i s unknown, i t would appear that t h i s estimate of p a r t u r i t i o n weight loss i s rather small. This i s partly a product of a few unidentifiable non-pregnant cows which were weighed through t h i s winter period. As they do not have an increase in weight similar to that of pregnant cows, their inclusion i n e v i t a b l y lowers the ov e r a l l estimate of the weight gain due to pregnancy. 1 0 3 Section 2 - The Influence of the garaaaeters The parameters influencing the weight of beef cows are numerous and varied. Those which were investigated in t h i s research are now discussed. The Seasonal E f f e c t was found to have a major influence on cow weight and separate analyses were car r i e d out to determine the parameters influencing the seasonal weight change per se. The re s u l t s from these analyses are included in the discussion of t h i s e f f e c t . Breedtype The confounding of the genetic and environmental parameters influencing cow weight in t h i s research l i m i t s independent consideration of the genetic components. However, the lack of significance of the Breedtype E f f e c t when i t i s Included in the i n d i v i d u a l analyses f o r herds 4, 5 and 8 indicates that, within these herds, cows of g e n e t i c a l l y d i f f e r e n t breeds and crosses have a s i m i l a r mean weight. As the breedtypes in herd 8 are B r i t i s h breeds, or crosses of B r i t i s h breeds, and the cows are managed as one unit, the r e s u l t in t h i s herd i s reasonable. In herds 4 and 5 approximately t h i r t y percent of the cows are crossbreds of exotic breeds, but most of these breedtypes are at least f i f t y percent composed of B r i t i s h breeds. The genetic influence of the larger exotic breeds (Mason, 1971; Adams et a l . , 1973) in these cows i s not, however, s u f f i c i e n t to cause them to be s i g n i f i c a n t l y heavier than th e i r straightbred, British-breedtype contemporaries. In herd 9, however, exotic crossbred cows are s i g n i f i c a n t l y heavier than th e i r B r i t i s h breedtype contemporaries. This difference could be due to more generous feed management i n t h i s 104 s m a l l herd. In these circumstances the e x o t i c c r o s s b r e d cows e x h i b i t a g r e a t e r growth p o t e n t i a l . Herd 2 i s composed of Hereford, Hereford x Shorthorn and a few Hereford x Angus cows. The l a c k of s i g n i f i c a n c e of the Breedtype E f f e c t i n d i c a t e s t h a t the i n c l u s i o n of t h i s herd without s p e c i f y i n g the breedtype of each i n d i v i d u a l i s not adding s i g n i f i c a n t l y t o the e r r o r term i n the a n a l y s e s . The net r e s u l t of t h e i r use i s thus advantageous, and the d e c i s i o n to i n c l u d e them without s p e c i f y i n g the breedtype i s thus v i n d i c a t e d . Fitzhugh et a l . (1967) and F i t z h u g h (1965) r e p o r t weight d i f f e r e n c e s between breedtypes w i t h i n ten s t a t e and f e d e r a l experimental s t a t i o n herds i n the southern United S t a t e s . The cows i n t h e i r study were of Hereford, Angus, Brahman and Santa G e r t r u d i s breeding, but the authors do not mention the breedtype composition of the c r o s s b r e d cows or the l e v e l of s i g n i f i c a n c e of the d i f f e r e n c e s . Herd I t i s apparent from the o u t l i n e d e s c r i p t i o n of the herds t h a t a heterogeneous sample of herds i s i n c l u d e d i n t h i s r e s e a r c h . I t i s not, t h e r e f o r e , s u p r i s i n g t h a t the Herd E f f e c t accounts f o r a l a r g e p r o p o r t i o n of the variance of the weight r e c o r d s . Fitzhugh (1965) and Fitzhugh et a l . (1967) a l s o found t h i s e f f e c t t o be a major f a c t o r determining the weight cf a beef cow. These authors r e p o r t that the between herd, w i t h i n breed weight d i f f e r e n c e s were l a r g e r than those between breeds w i t h i n herds The environmental and g e n e t i c parameters i n c l u d e d i n t h i s 105 Herd Effect were mentioned i n Chapter 5, but i t i s impossible to assess objectively t h e i r r e l a t i v e importance. It i s l i k e l y , however, that a large portion of the between herd variance i s due to environmental factors. Thus, the major reason why the cows in the pasture herds are 119 l b . heavier than those i n the range herds i s that more nutrients were available to the cows in the pasture herds i n both summer and winter. Edwards and Bailey (1975) also report that cows grazing summer pasture are heavier than those grazing summer range. They report a 160 l b . difference between herd types but make no mention of winter feeding. S i m i l a r l y , the inconsistent difference between the mean weight of straightbred and crossbred herds on range and pasture i s l i k e l y to be a product of environmental rather than genetic factors. This herd x environment interaction i s s i m i l a r to the breedtype x environment interaction reported by Kilkenny and St o l l a r d (1973). These B r i t i s h workers found that the mean weight of a breedtype depended on whether i t was located i n a lowland, upland or h i l l herd. In thi s study, however, the only relat i o n s h i p between weight and location i s the range/pasture difference. Age As expected, the rapid increase i n weight of younger cows declines with age. Thus at two years of age a cow weighs 78% of her maximum weight, but during the following four years of her l i f e her weight only increases each year by approximately 8%, 6%, 3% and 3% respectively. In t h i s study a cow's weight i s stable at six and seven years of age and then increases again 106 through the f o l l o w i n g two years. Although the 25.8 l b . i n c r e a s e i n weight between s i x - and n i n e - y e a r - o l d cows i s s i g n i f i c a n t s t a t i s t i c a l l y i t would not appear to be so b i o l o g i c a l l y . There i s c e r t a i n l y no apparent b i o l o g i c a l e x p l a n a t i o n f o r such a delayed p e r i o d of growth. The d e f i n i t i o n of the nature weight of a cow was d i s c u s s e d i n chapter 1. In t h i s study i t i s d e f i n e d as t h a t weight to which no f u r t h e r s i g n i f i c a n t annual increments are added. T h e r e f o r e , the cows i n t h i s r e s e a r c h reach t h e i r mature weight at s i x years of age, at which time t h e i r mean weight i s 1083.9 l b . However, i t i s apparent t h a t t h e r e i s a c o n s i d e r a b l e between herd v a r i a t i o n i n t h i s p a t t e r n of growth. I f the anomalous estimates of the mean weights i n herd 3 are excluded, mature weight and age v a r i e d between 1068.2 l b . at f i v e years of age ( i n herd 4) and 1228.0 l b . at nine years of age ( i n herd 7). As d i s c u s s e d i n S e c t i o n 1, t h i s v a r i a t i o n i s probably due to environmental d i f f e r e n c e s between herds. Fitzhugh (1965) and Fitzhugh et a l . (1967) r e p o r t a s i m i l a r v a r i a t i o n i n mature age (6-12years) but a c o n s i d e r a b l y g r e a t e r v a r i a t i o n i n mature weight (maximum d i f f e r e n c e 313 lb.) amongst the ten herds i n t h e i r study. These herds, however, co n t a i n e d a more d i v e r s e s e l e c t i o n of breedtypes than those found i n the herds i n the present study. The d e c l i n e i n the weight of o l d e r cows r e p o r t e d by Knox and Roger (1949), C l a r k et a l . (1958) and B r i n k s et a l . (1962) was not apparent i n the o v e r a l l age estimates i n t h i s study. However, environmental f a c t o r s i n herds 4, 5, 6 and 8 d i d cause the cows i n these herds to l o s e weight a f t e r maturity. 1 0 7 Year The year of r e c o r d dees not i n f l u e n c e the o v e r a l l mean or the age s u b c l a s s mean weights i n t h i s study. However, w i t h i n t h i s n o n - s i g n i f i c a n t Year E f f e c t each herd does have a v a r i a t i o n i n i t s mean annual weight. A s i m i l a r random v a r i a t i o n a c r o s s herds was r e p o r t e d by Fitzhugh (1965) and Fitzhugh e t a l , (1967), In a l l herds except herd 1, the between year v a r i a t i o n s i n weight are r e l a t i v e l y s m a l l and presumably r e f l e c t minor environmental v a r i a t i o n s w i t h i n each herd. S i m i l a r v a r i a t i o n s i n response to environmental f a c t o r s were found by C l a r k et a l . (1958), Brown and Franks (1964) and O r i c k et a l . (1971). The f a c t o r s a s s o c i a t e d with the weight changes i n herd 1 have a l r e a d y been d i s c u s s e d . Season The season of weighing i s a major parameter i n f l u e n c i n g the weight of the cows i n t h i s study. The mean i n c r e a s e i n weight of 114.2 l b . between s p r i n g and f a l l i s a product o f the f o l l o w i n g f a c t o r s : 1) The s u p e r i o r n u t r i t i o n a v a i l a b l e t o cows d u r i n g the summer. 2) The s t r e s s due to pregnancy, p a r t u r i t i o n and e a r l y l a c t a t i o n i n f l u e n c i n g s p r i n g but not f a l l weight. 3) The p o s s i b i l i t y of the weight of the f o e t u s and i t s a s s o c i a t e d t i s s u e s and f l u i d s being a component of a cow's f a l l weight. However, S a l i s b u r y and Van Demark (1961) r e p o r t t h a t the weight of the f o e t u s and i t s a s s o c i a t e d t i s s u e s and f l u i d s i s l i k e l y t o be r e l a t i v e l y s m a l l i n the f a l l (see l a t e r ) . The i n f l u e n c e o f e a r l y l a c t a t i o n s t r e s s i s minimized i n t h i s 108 r e s e a r c h by e l i m i n a t i n g weight records which have a s p r i n g i n t e r v a l of more than seventy days. Conseguently, the other f a c t o r s mentioned above are the main reasons f o r t h i s s e a s o n a l weight change. The only p r e v i o u s study which has re p o r t e d a seasonal weight change of s i m i l a r magnitude i s t h a t of J e f f r e y and Berg (1971). The cows i n t h e i r study had a summer weight g a i n and winter weight l o s s of 150 l b . and 133 l b . r e s p e c t i v e l y . In comparison, Vacarro and D i l l a r d (1966) r e p o r t a 180-day summer weight gain of 32 l b . , and Fitzhugh (1965) and F i t z h u g h et a l . (1967) r e p o r t a mean seasonal weight d i f f e r e n c e of only 19 l b , A summer weight l e s s of 61 l b , was r e p o r t e d by Singh e t a l . (1970) . Amongst the other s t u d i e s mentioned i n Chapter 2, the re p o r t by Joandet and Cartw r i g h t (1969) c o n t a i n s no q u a n t i t a t i v e estimate, while t h a t recorded by Ewinq e t a l . (1965) i s not comparable. The s t u d i e s of Brinks et a l . (1962), C l a r k et a l . (1958) and Anderson et a l . (1973) are concerned with pre-partum s p r i n g weiqhts. The unknown weight of the f o e t u s and a s s o c i a t e d t i s s u e s i n c l u d e d i n t h i s weight p r e c l u d e s any r e l i a b l e comparison of the seasonal weight changes i n these s t u d i e s with the present e s t i m a t e . The d i f f e r e n c e between the comparable r e p o r t s of s e a s o n a l weight change i s l i k e l y to be the r e s u l t of the i n t e r a c t i o n of the f o l l o w i n g two f a c t o r s : 1) These other s t u d i e s have i n v o l v e d r e s e a r c h herds. In comparison with most of the herds i n the present study, the winter feed management i n such herds i s l i k e l y t o be r e l a t i v e l y 1 0 9 l i b e r a l . Thus, the cows calve in good condition in the spring and have only a small (or zero) need to increase in weight through the summer. In contrast, the cows i n t h i s study calve i n r e l a t i v e l y poor condition and have larger summer weight gains. 2) The studies of Vacarro and D i l l a r d (1966), Fitzhugh (1965), Fitzhugh et a l . (1967) and Singh et a l . (1970) were carr i e d out in the southern half of the United States. The present study and that of Jeffrey and Berg (1971) were carried out north of the 49th p a r a l l e l of l a t i t u d e . The more severe winters i n Canada could be another reason for the larger seasonal fluctuations i n weight, A variation i n seasonal weight change has also been recorded within the present study. The parameters which influence the magnitude of these changes in weight w i l l now be discussed. Those which can be d i r e c t l y related to absolute weight, i . e . spring i n t e r v a l and the parameters associated with the c a l f , w i l l , however, be discussed per se l a t e r i n t h i s section of the discussion. Breedtype - t h i s factor was never s i g n i f i c a n t i n any of the i n d i v i d u a l analyses for herds with more than one breedtype. It i s thus apparent that, within a herd, the variation in seasonal weight change occurs independently of genetic, breedtype differences. As i n the absolute weight analysis, t h i s r e s u l t vindicates the decision to include the records from herd 2 without specifying the breedtype of each cow. Previous change i n weight- as mentioned i n section 1, t h i s parameter has a major influence on the seasonal weight changes recorded in t h i s study. The regression c o e f f i c i e n t s f o r a l l the 110 previous change in weight covariables are negative. Thus, as would be expected, there i s a positive compensatory gain i n the summer i n response to a winter weight l o s s , and a negative compensatory gain in the winter in response to a summer weight increase. The negative compensatory winter gain i s , however, not s i g n i f i c a n t i n two-year-old cows. At thi s age the summer weight gain undoubtedly r e f l e c t s growth of muscle and, to a lesser extent, s k e l e t a l tissue. The weight gain due to such growth i s not easily l o s t , and the effect of the covariable i s not s i g n i f i c a n t . The r e l a t i v e l y small regression c o e f f i c i e n t s i n the three- and four-year-old subclasses also r e f l e c t s i m i l a r summer growth (mean b--0.4561). In older cows a summer weight gain r e f l e c t s a change i n condition, which i s more e a s i l y l o s t in a subsequent winter. Hence, the greater r e l a t i o n s h i p between the weight changes (mean b = -0.6024). Conversely, the winter weight loss i n each age subclass i s mostly a loss i n condition. Thus there i s no b i o l o g i c a l reason why the subsequent compensatory gain should vary across ages. This i s refl e c t e d in the more equivalent values for the covariable across ages i n the summer change i n weight analysis. It i s apparent that the positive compensatory gain i n the summer (mean b = -0.6811) is greater than the negative gain during the winter (mean b = -0.5194). Again t h i s i s a product of the tissue changes involved. As the negative winter gain i s r e l a t i v e l y small and the larger positive compensatory gain occurs on r e l a t i v e l y inexpensive summer range/pasture, t h i s b i o l o g i c a l r e l a t i o n s h i p i s an asset to a farmer or rancher. 111 Herd - the other parameter which has a major influence on these seasonal weight changes i s the Herd E f f e c t . As mentioned i n section 1, t h i s parameter w i l l be discussed by considering the herd estimates which include the compensatory growth component. The reasons for the between herd differences i n weight change could be both genetic and environmental. However, i t appears that both the summer and winter weight changes in a herd are very much dependent on the winter feed management i n that herd. A herd which i s r e l a t i v e l y well fed in the winter, e.g. herd 1, has a small weight gain in the winter. I t s subsequent compensatory gain i s thus negative and i t s summer weight gain i s small. The opposite occurs i n herd 3. Its winter feeding i s very poor and t h i s r e s u l t s in a very larqe winter weiqht loss, a subsequent larqe po s i t i v e compensatory qain and thus a larqe t o t a l summer weiqht qain. Thus, i f the herds are ranked accordinq to t h e i r weight changes, the order of ranking i s the same for both summer and winter weight, even though the former i s expressed as a percentage of body weight. The cows i n the pasture herds in thi s study (herds 5, 6 and 7) are s i g n i f i c a n t l y heavier than those in range herds. Their heavier weights could be a result of either a smaller winter weight loss or a greater summer weight gain, or both. There i s some ind i c a t i o n that the former i s occurring in t h i s study. As a res u l t of t h i s , there i s less compensatory growth i n the summer and the summer weight gain consists of a r e l a t i v e l y large proportion of *new weight increase*. Thus, even though these cows do not have esp e c i a l l y large summer weight gains, the net 1 1 2 r e s u l t i s that they are r e l a t i v e l y heavy. In the present r e s e a r c h seven of the e i g h t herds s t u d i e d l o s t weight over the winter. Fitzhugh (1965) and Fitzhugh e t a l . (1967) a l s o found t h a t i n a l l but one of the s i x herds f o r which they c o u l d estimate seasonal weight change there was a winter weight l o s s . The winter weight changes r e p o r t e d by these authors v a r i e d between a weight l o s s of 50 l b . and the one weight g a i n of 62 l b . Vacarro and D i l l a r d (1966) a l s o r e p o r t a sm a l l d i f f e r e n c e i n summer weight g a i n between the two herds i n t h e i r study. D i f f e r e n c e s can a l s o be found between the s i n g l e - h e r d s t u d i e s using pre-partum s p r i n g weights which were d e s c r i b e d i n chapter 2. Ajje - the i n f l u e n c e of t h i s parameter v a r i e s between the summer and winter weight changes. The winter feed management and the s t r e s s of pregnancy, p a r t u r i t i o n and l a c t a t i o n causes each age s u b c l a s s to l o s e a s i m i l a r amount of weight over the winter. These f a c t o r s are thus s u f f i c i e n t to i n h i b i t c ompletely a young cow's in h e r e n t need t o grow. In the summer the a v a i l a b i l i t y of feed i s not l i m i t e d by the i n t e r v e n t i o n of man. Thus, younger cows are a b l e t o express t h e i r inherent need to grow, and t h e i r weight gains are s i g n i f i c a n t l y g r e a t e r than those o f o l d e r cows. Thus the cows i n t h i s study are i n c r e a s i n g i n weight over age as a product of l a r g e r summer weight gains i n younger a n i m a l s , and not as a r e s u l t of any d i f f e r e n c e s between ages i n winter weight changes. The r e l a t i o n s h i p between summer weight g a i n and age does show minor d i f f e r e n c e s between herds, but the g e n e r a l p a t t e r n i s the same i n each herd. In the herds where winter f e e d i n g was 113 more l i b e r a l , i . e . those included in the winter change in weight analysis, two- and three-year-old cows tend to have a smaller weight loss, or even a gain in weight, during the winter. But o v e r a l l , age i s s t i l l not a s i g n i f i c a n t source of variation amongst the weight change records. S i m i l a r l y , the year of record did not influence t h i s pattern of seasonal weight change over age. Vacarro and D i l l a r d (1966), Fitzhugh (1965), Fitzhugh et a l . (1967) and Brinks et a l . (1962) also recorded a s i m i l a r d i f f e r e n t i a l summer weight gain over age, while England et a l . (1961) found that summer weight gain i s not associated with age. However, no reason f o r t h i s exception i s apparent i n the report on the l a s t of these studies. During the winter Fitzhugh (1965) and Fitzhugh et a l . (1967) recorded a greater weight loss from f a l l to post-partum weighing in cider cows. Brinks et a l . (1962) found greater weight gains from f a l l to pre-partum weighing i n younger cows. The winter feed management i n research herds such as those in these studies has previously been discussed and i s considered to be more l i b e r a l than that in most of the herds i n the present study. It seems l i k e l y that these reports of an Age Ef f e c t on winter weight change are a product of t h i s winter feeding. Year - overall the year of record did not influence these seasonal weight changes. Nevertheless, environmental differences between years did cause minor annual v a r i a t i o n in weight change in some herds, e.g. winter weight change i n herd 2. The one exception to t h i s i s herd 1; the anomalous weight changes i n t h i s herd have already been discussed. The comprehensive 114 investigation of t h i s between herd variance was, however, limited by the nature of the data. Spring i n t e r v a l After p a r t u r i t i o n a cow i s la c t a t i n g to provide nutrients for her c a l f ; the peak of her lactation curve occurs soon after p a r t u r i t i o n . During this spring i n t e r v a l period (mean length 26 days ± 14days) the cows i n t h i s study lose 0.7 l b . per day. It would thus appear that the weight of a cow i s influenced by her milk production during t h i s spring i n t e r v a l . However, the weight of a cow can only be related to time, any re l a t i o n s h i p of weight with the l e v e l of milk production cannot be estimated. Vacarro and D i l l a r d (1966) also recorded a loss i n weight during the f i r s t sixty-day period post-partum. After t h i s point-there was a summer weight gain. The mean weight loss in t h i s study, however, was approximately 0.3 lb. per day. These workers found that i n older cows t h i s weight loss had a s i g n i f i c a n t negative c o r r e l a t i o n with c a l f weight gains; an indicatio n that, at least in older cows, weight loss i s associated with milk production (Koch, 1972). Amir and K a l i (1974) report that i n early l a c t a t i o n dairy cows are frequently unable to eat s u f f i c i e n t to meet the energy cost of l a c t a t i o n and they consequently mobilize body reserves. A weiqht loss immediately post-partum i s thus a common and accepted phenomenon i n dairy cows. Calf age x Calf sex x Calf weaning weiqht In t h i s study none of the parameters associated with the ca l f being suckled through the summer period influence the cow's weight change. Thus any e f f e c t which the sex of a c a l f might 115 have on i t s dam's milk production (Rutledge e t a l . , 1971; Pope S i i l l * r 1968) i s not s u f f i c i e n t to i n f l u e n c e her weight. S i m i l a r l y , the l a c t a t i o n s t r e s s d e s c r i b e d i n chapter 5 which might be a s s o c i a t e d with the age of a c a l f does not i n f l u e n c e cow weight. The l a c k o f s i g n i f i c a n c e of weaning weight i n d i c a t e s that the i n f l u e n c e of l a c t a t i o n on cow weight, which was apparent immediately post-partum, does not l a s t through the summer. The r e l a t i o n s h i p between the dam and i t s c a l f d u r i n g the summer i s a r e c i p r o c a l one. Thus the converse i n t e r p r e t a t i o n of previous s t u d i e s i n which the weight change of the dam i s cons i d e r e d i n r e l a t i o n to i t s i n f l u e n c e on c a l f weaning weight are e q u a l l y v a l i d . The c o n c l u s i o n of J e f f r e y and Berg (1971) i s t h e r e f o r e the same as t h a t of the present r e s e a r c h . However, the c o n c l u s i o n s of Vacarro and D i l l a r d (1966) and Singh et a l . (1970) do not agree with the present r e s e a r c h . The d i f f e r i n g r e s u l t s i n these s t u d i e s can be a s s o c i a t e d with the magnitude of the summer weight changes recorded i n them. As mentioned p r e v i o u s l y , a 150 l b . summer weight g a i n was re p o r t e d by J e f f r e y and Eerg, (1971) while Vacarro and D i l l a r d (1966) recorded only a 32 l b . weight gain and Singh et a l . (1970) a c t u a l l y r e p o r t a summer weight l o s s . Thus, i f the cows have a s m a l l or neg a t i v e weight g a i n , a s i g n i f i c a n t r e l a t i o n s h i p i s apparent between the cow and c a l f weights. However, when the summer weight g a i n i s l a r g e , the i n f l u e n c e of the c a l f i s r e l a t i v e l y s m a l l and weaning weight does not s i g n i f i c a n t l y a f f e c t cow weight. 116 Pregnancy, and p a r t u r i t i o n As expected, a cow's stage of pregnancy i s a s i g n i f i c a n t parameter influencing her weight. The mean weight of the cows in herd 2 used in t h i s study, increases by 101.4 l b . between the 90th and 260th day of pregnancy. After t h i s point there i s a mean weight loss of 6.8 lb. prior to p a r t u r i t i o n . A weight loss in the l a s t days cf pregnancy has also been observed in dairy c a t t l e (Hodges, 1976), but a physiological explanation for t h i s loss has not been documented. It can be speculated that i t i s due to one or both of the following factors: 1) A change i n the amount of digesta present i n the rumen during t h i s period. 2) If the cow i s having to metabolize her body reserves pre-partum to support the c a l f and i t s associated tissues, her own weight loss i s masked through most of pregnancy by the increasing weight of the conceptus. However, af t e r the 260th day of pregnancy the rate of weight increase i s r e l a t i v e l y small and the net result i s a weight loss. The mean weight loss at p a r t u r i t i o n i s 80.0 l b . or 7.2.% of the cows pre-partum weight. This estimate i s le s s than the 131.6 l b . weight loss reported by Ewing et a l . (1972). In t h e i r study t h i s weight loss was 13.1% of the pre-partum weight of the cow. The reason for t h i s r e l a t i v e l y small weight loss estimate in the present study was discussed i n Section 1. The weight loss during the l a s t ninety days of pregnancy, including p a r t u r i t i o n weight l o s s , i s 50.7 l b . This weight loss i s , however, similar to the 68.0 l b . loss during the same period reported by Vacarro and D i l l a r d (1966). 1 1 7 There i s a l s o a weight l o s s from the f a l l through to p a r t u r i t i o n . T h i s 21.2 l b . l o s s could p a r t l y be due to the i n f l u e n c e of pregnancy i n the f a l l , when the cows are on average 129 days pregnant ( S a l i s b u r y and Van Demark, 1961). I t i s l i k e l y , however, that t h i s d i f f e r e n c e i s a l s o due to a change i n the weight of the cow per se. S e c t i o n 3 - C o n c l u s i o n s The d i s c u s s i o n i s concluded by s y n t h e s i z i n g the most s a l i e n t p o i n t s which a r i s e from t h i s r e s e a r c h . Although such c o n c l u s i o n s apply only to the herds i n c l u d e d i n t h i s r e s e a r c h , most of them a l s o have i m p l i c a t i o n s which extend o u t s i d e t h i s • u n i v e r s e * . These c o n c l u s i o n s are as f o l l o w s : 1) A herd operator e x e r t s a major i n f l u e n c e over the weights of the cows i n h i s herd. T h i s human i n f l u e n c e i s present i n the l a r g e Season, Herd, and Herd x Season E f f e c t s . 2) The weight changes of the cows i n herd 1 show the b i o l o g i c a l upper l i m i t of t h i s human i n f l u e n c e . Overfeeding of these cows led t o an a t y p i c a l summer weight l o s s . 3) The season of weighing has a major i n f l u e n c e on cow weight. Normally there i s a l e s s i n weight dur i n g the winter and i n the i n i t i a l p e r i o d post-partum. T h i s i s f o l l o w e d by an i n c r e a s e i n weight through the summer. 4) Each seasonal change i n weight c o n s i s t s of a compensatory weight change, which can be e i t h e r p o s i t i v e ( i n the summer) or negative (in the w i n t e r ) , and a »new weight change*. The compensatory gain i s dependent on the weight change i n the previous p e r i o d , while the *new weight change* i s more d i r e c t l y 118 related to the a v a i l a b i l i t y of nutrients during the period of change. Thus the winter feed management of an operator has an influence over both the summer and winter weight changes in his herd. 5) This seasonal v a r i a t i o n in cow weight does not necessarily occur around the animal's expected or true mean weight. 6) Within a herd, genetically d i f f e r e n t breedtypes have the same seasonal weight changes. 7) The seasonal weight change recorded i n t h i s research i s considerably greater than that reported i n most previous studies. This i s considered to be a conseguence of, i) the location of the studies, i i ) better winter feeding in the research herds included in these previous studies. 8) A s i g n i f i c a n t portion of the between herd differences in weight i s l i k e l y to be related to the a v a i l a b i l i t y of nutrients (both in summer and winter) in each herd. Thus, the weight of a cow i s dependent on her herd environment. 9) Within a herd there i s normally no difference between the mean weights of genetically d i f f e r e n t breedtypes. There i s some ind i c a t i o n , however, that where the feed supply i s more l i b e r a l such a difference does e x i s t . However, to confirm t h i s , further research would be necessary. 10) The mean age at maturity is six years. The mean growth curve up to and beyond t h i s point has a s i g n i f i c a n t l i n e a r and quadratic component. Environmental differences between herds cause a variation in the age at maturity and the shape of the growth curve. 119 11) During the summer younger cows i n c r e a s e i n weight more than o l d e r cows, but d u r i n g the winter a l l ages l o s e e q u i v a l e n t amounts of weight. Thus cows are i n c r e a s i n g i n weight over age owing to l a r g e r summer weight g a i n s , and not to any d i f f e r e n c e s i n winter weight change. 12) The c a l f being suckled by a cow through the summer p e r i o d has no i n f l u e n c e on her summer weight g a i n . T h i s r e s e a r c h has d e s c r i b e d and evaluated many of the environmental parameters which T a y l o r (1965) and Joandet and C a r t w r i g h t (1969) mentioned as being p o t e n t i a l l y important i n f l u e n c e s on the growth p a t t e r n of a cow. In the environments i n c l u d e d i n t h i s r e s e a r c h i t i s apparent t h a t these parameters have a major i n f l u e n c e on the phenotypic e x p r e s s i o n of a cow's genotype f o r growth. The nature of the a v a i l a b l e data has, however, l i m i t e d the e v a l u a t i o n of the p o s s i b l e g e n e t i c parameters i n f l u e n c i n g growth to maturity. The d i f f i c u l t y i n s e p a r a t i n g the i n f l u e n c e of these anvironmental and g e n e t i c parameters i s r e f l e c t e d i n the l i m i t e d p u b l i s h e d data on the l a t t e r aspect of growth i n beef cows. Further r e s e a r c h to i n v e s t i g a t e the g e n e t i c component would r e q u i r e the i n c l u s i o n of breeding r e c o r d s , and would have to be c a r r i e d out over s e v e r a l generations of breeding. The present r e s e a r c h emphasizes t h a t such s t u d i e s would be meaningless without some s p e c i f i c a t i o n or c o n t r o l o f environmental c o n d i t i o n s . The l a r g e s e a s o n a l weight changes recorded i n t h i s r e s e a r c h suggest an i n t e r e s t i n g management o p t i o n f o r a beef producer. I f he a l l o w s h i s cows to l o s e weight through the winter and then 1 2 0 regain i t daring the following summer, he can reduce his winter feed costs. The l i m i t a t i o n of such a management practice, however, i s i t s e f f e c t on the cow's productivity, as reflected i n her a b i l i t y to raise a good sized c a l f each year. In dairy c a t t l e i t has been found (Hodges 5 Hiley, unpublished) that the magnitude of the weight loss i s not the most important factor a f f e c t i n g f e r t i l i t y , i . e . the a b l i l i t y to produce a c a l f each year. If the body weight of a cow i s increasing during the breeding period, t h i s w i l l o f f s e t the decreased f e r t i l i t y which might res u l t from a weight loss. Thus, as the cows i n herds 3 and 8 were presumably increasing in weight during breeding, the large weight loss in these herds might not have had a detrimental influence on f e r t i l i t y . A study of conception rates in these herds, or others which have a s i m i l a r seasonal weight loss, could usefully be carried out to investigate these relationships i n beef c a t t l e . However, i f a large winter weight loss causes a cow to raise a r e l a t i v e l y small calf i n the subsequent f a l l , a policy of allowing a larqe winter weiqht loss would, perhaps, not be expedient, Research to investiqate these factors i s currently being carried out. It i s also apparent from the present r e s u l t s that larqe weiqht qains, of both cows and calves, occured during summer qrazinq of rangeland. Although the summer weight gain i n a herd varied according to the magnitude of the winter weight loss, i t would also have been dependent on factors such as the guality of the summer grazing, stocking rate and the amount of p r e c i p i t a t i o n . Also there could have been genetic differences in 121 growth rate between the herds. A study to ascertain the range type/plant species which were associated with large weight gains, as well as the other environmental differences responsible for the between herd v a r i a t i o n i n summer weight gain, would y i e l d u s e f u l l information for future range management policy decisions in t h i s province. However,such a study over the extensive area of rangeland included i n t h i s research would be a large task. I t was thus considered to be outside the scope of the present research. The weight loss which was observed immediately post-partum i s s i m i l a r to that observed in dairy cows. Although i t i s impossible for a high y i e l d i n g dairy cow to consume s u f f i c i e n t feed to prevent t h i s less (without disturbing the reguired roughage- concentrate r a t i o ) , an increased l e v e l of feeding could possibly prevent i t i n beef cows. It might also increase milk y i e l d and c a l f weight gains. However, i f the c a l f i s too young i n the f i r s t few weeks post-partum to u t i l i z e a more p l e n t i f u l supply of milk, and e s p e c i a l l y i f i t results in their developing c a l f scours, t h i s would not be a b e n i f i c i a l management policy. But i f the weight loss continues through a longer period, such as the six t y days considered by Vacarro & D i l l a r d (1966), additional feeding at some stage might be advantageous. A study involving more freguent weighing and controlled feeding immediately post partum i s reguired to resolve t h i s uncertainty. 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Genetic analysis of maturing. J . Anim. Sci. 33: 717-725. Francois, J. J., D. W. Vogt and J. C. Nolan. 1973. H e r i t a b i l t i y of and genetic and phenotypic correlations among some economically important t r a i t s of beef c a t t l e . J. Anim. S c i . 36: 635-639. Guilbert, H. R. and P. H. Gregory. 1952. Some features of growth and development of Hereford c a t t l e . J. Anim. S c i . 11: 3-16. Harvey, W. R. 1975. Least-sguares analysis of data with unegual subclass numbers. U.S.D.A., A.R.S. B u l l . H-4. Henderson, C. R. 1953 estimation of variance and covariance components. Biometrics 28: 226-252. Hodges, J. H. 1976. Personal communication. Holloway, J. W. and R. Totusek. 1973. The relationship between pre-weaning n u t r i t i o n a l management and the growth and development of Angus and Hereford females. J. Anim. S c i . 37: 800-806. Jeffr e y , H. B., R. T. Berg and R. T. Hardin. 1971. Factors affecting pre-weaning performance in beef c a t t l e . Can. J. Anim. S c i . 57: 561-577. Jeffr e y , H. B. and E. T. Berg. 1972. An evaluation of several measurements of beef cow siz e as related to progeny performance. Can. J . Anim. S c i . 52: 23-27. Joandet, P. E. and T. C. Cartwright. 1969. The estimation of e f f i c i e n c y of beef production. J. Anim. Sci. 29: 862-868. Johannsen, I. and S. E. Hildman. 1954. The relat i o n s h i p between certain body measurements and l i v e and slaughter weight i n c a t t l e . Anim. Breed. Abst. 22: 1-16. Kilkenny, J. R. and R. J . S t o l l a r d , 1973. Bodyweight in suckler cows and i t s r e l a t i o n to c a l f performance. Meat and livestock Commision, Bletchley, Milton Keynes, G.B. Klosterman, E. W. 1972. Beef c a t t l e s i z e for maximum e f f i c i e n c y , J. Anim. S c i . 34: 875-880. Knox, J. M. and M. Roger. 1945. The ef f e c t s of age on the weight and production of beef cows. Cattlemen 32: 22-29. Roger, M. and J. M. Knox. 1951. The correlation between gains made at d i f f e r e n t periods by c a t t l e . J. Anim. S c i . 10: 760-767. 126 Lowman, B. 1975. Methods of condition scoring suckler cows. E.C.B.C. Digest 30: 30-35. Mason, I. L. 1971. Comparative beef performance of the large c a t t l e breeds of western Europe. Anim. Breed. Abst. 39: 1-24. McMeekan, C. P. 1940. Growth and development in the pig with special reference to carcass quality characters. I I I . The eff e c t of plane of n u t r i t i o n on the form and composition of the bacon piq. J. Aqric. S c i . 40: 511-569. Meat and Livestock Commission, -1975. An investigation of body condition i n suckler herds. Meat and Livestock Commission, Bletchley, Milton Keynes, G.B. Moore, D. B., H. H. Stonaker, and K. Riddle. 1961. Factors influencing comparisons of Hereford b u l l s for rate of qain. J. Anim. S c i . 20: 255-259. O'Mary, C. C , T. L. Brown and M. E. Ensminqer. 1959. Correlation of cow measurements to 180 day adjusted weaninq weiqht of t h e i r calves. J. Anim. S c i . 18: 1471. abst. Peterson, R. G. 1974. Personal communication. Pope, L. S., L. Smithson, D. F. Stephens, D. 0. Pinney And M. Velasco. 1968. Factors a f f e c t i n g milk production of range beef cows. Okla. Agric. Exp. Sfn. Misc. Pub. 70: 69-77. Preston, T. R. and M. S. W i l l i s . 1960. Intensive beef production. Oxford:Pergamon Press. Rutledge, J. J., 0. W. Robinson, W. T. Ahlschwede And J. E. Legates. 1971. Mild y i e l d and i t s influence on 205 day weight of beef calves. J . Anim. S c i . 33: 563-567. Salisbury, G. W. and N. L. VanDemark. 1961. Physiology of reproduction and a r t i f i c i a l insemination. San Francisco:Freeman. Searle, S. R. and C. R. Henderson. 1961. Computing proceedures for estimating components of variance in the two-way c a l s s i f i c a t i o n , mixed model. Biometrics 17: 607-616. Simpson, M. J., L. L. Wilson, J. H. Zie g l e r , 1. G. B l a i r and H. Varela-Alvarez. 1972. The relationship of cow weights, measures and scores with progency c h r a c t e r i s t i c s i n an Angus/Holstein herd. J. Anim. S c i . 34: 185-192. Singh, A. B., R. R. Schalles, W. M. Smith and F. B. Kessler, 1970. Cow weight and pre-weaning performance of cows. J. Anim. S c i . 31: 27-30. Tanner, J . E., R. J. Cooper and W. E. Kruse 1965. The relationship between weaning weight of calves and 127 measurements of the i r dams. J. Anim. S c i . 24: 280. abst. Taylor, St. C. S. 1963. Accuracy i n measuring c a t t l e with special reference to i d e n t i c a l twins. Anim. Prod. 5: 105-115. Taylor, St. C. S. 1965. A r e l a t i o n between mature weight and time taken to mature in mammals. Anim. Prod. 7: 203-220. Thiessen, R. 1976. The relat i o n s h i p between body siz e and e f f i c i e n c y in beef cow/calf production. B.C.B.C. Digest 31: 63-66. Orick, J. S., B. w. Knap, J. S. Brinks, 0. F. Pahnish and T. M. Riley. 1971. The rel a t i o n s h i p between cow weights and c a l f weaning weights in Angus, Charolais and Hereford breeds. J. Anim. S c i . 33: 343-348. Vacarro, Rodolfo And E. 0. D i l l a r d . 1966. The relationship of dam's weight and weight changes to c a l f ' s growth rate i n Hereford c a t t l e . J. Anim. Sci. 25: 1063-1068. Yates, F. 1934. The analysis of multiple c l a s s i f i c a t i o n with unequal numbers in di f f e r e n t classes. J. Am. Stat. Assoc. 29: 51-74. 1 2 8 Least sguares constants for each degree cf freedom f i t t e d IS ik§ analysis for Sjgrjjg and F a l l weights j Subclass | L.S. Constant | S.E. | j Herd 1 | 1 1 . 2 j 4.7 | I 2 | - 4 8 . 1 \ 3 . 6 | J 3 | - 1 5 4 . 2 | 4 . 8 | I 4 | - 2 4 . 0 J 7 . 0 I \ 5 | 6 4 . 0 | 9 . 4 J I 6 J 5 6 . 0 i 1 3 . 0 I 1 7 | 6 4 . 0 | 6 . 8 | I 7 | 1 0 . 2 | 6 . 7 i | Age 2 | - 1 4 8 . 5 j 5 . 5 J j 3 i - 6 8 . 8 | 5 . 2 1 | 4 | 0 . 9 | 5 . 8 | | 5 I 3 8 . 4 1 6 . 3 i | 6 | 6 4 . 5 | 7 . 9 j | 7 | 5 6 . 5 | 9 . 3 | | 8 | 7 1 . 6 J 6 . 5 J \ 9 i 9 0 . 3 i 9 . 9 j Year 1 | - 2 . 9 I 4 . 0 2 I 4 . 9 | 3 . 5 | Spring j - 5 7 . 1 | 2 . 7 J j . i „ i I I I I j Hd. 1 Yr. 1 | - 5 4 . 1 } 5 . 8 1 J 2 1 | 1 8 . 1 | 6. 6 1 | 3 1 | — 2 C . 7 ) 6 . 2 { | 4 1 i 2 4 . 9 | 8. 9 i | 5 1 | 2 4 . 9 l 1 0 . 4 | ! 6 1 | - 3 2 . 5 | 17 . 8 | | 7 1 | 2 4 . 9 | 8. 9 | | 1 2 1 3 0 . 9 | 5. 5 i 1 2 2 1 - 2 6 . 8 | 4 . 7 | 1 3 2 | 2 . 2 1 6 . 7 J 1 4 2 | 0 . 7 I 7 . 1 | J 5 2 J - 6 . 2 J 9. 5 J I 6 2 I 1 3 . 2 J 1 3 . 5 J 1 7 2 1 - 2 . 7 1 8 . 3 1 i 1 i j 129 4. 2 4. 0 4. 8 7. 4 8. 9 11. 3 6. 1 9. 5 8. 2 10. 8 9. 9 15.3 21. 2 15. 3 9. 7 7. 4 12. 0 10. 2 13. 9 20. 4 15. 8 10. 6 7. 5 12. 1 13. 2 14. 1 27. 8 14. 1 11. 9 8. 0 12. 3 13. 8 15. 4 32. 3 13. 6 13. 6 9. 9 12. 2 15. 0 19. 7 43. 7 16. 5 14. 5 11. 0 12. 9 17. 6 21. 3 20. 7 r T I 1 8 | - 2 1 . 3 I 11.5 I 2 8 | 36.4 | 9.1 I 3 8 | -23 .4 | 10.9 I 4 8 | - 16 .4 | 19.3 ! 5 8 | - 40 .6 | 18.6 J 7 8 | 54.3 j 17.7 1 1 9 | - 3 3 . 7 i 14. 1 I 2 9 | 20.1 j 11.7 i 3 9 J - 34 . 8 | 14.0 j 4 9 | - 43 . 7 | 16.9 I 5 9 | 7.8 ] 26. 8 I 6 9 | 16.0 | 53.1 I 7 9 | 67.6 | 23.6 I Age 2 Yr. 1 j 3.6 ) 6. 8 I 3 1 | - 0 . 7 | 7.1 I 4 1 1 13.3 J 6.4 J 5 1 | - 3 . 2 | 6.3 I 6 1 i - 1 6 , 3 1 7. 6 I 7 1 | - 8 . 8 | 7. 8 | 8 1 1 4.9 | 7.3 1 9 1 | 1.9 I 8. 1 J 1 2 | 9.2 | 11.8 I 2 2 I - 1 2 . 5 1 6.3 1 3 2 | 17.0 | 5. 2 I 4 2 I - 4 . 8 I 5.2 I 5 2 I 3.1 I 5. 8 l 6 2 | 4.6 | 5.9 I 7 2 | - 2 . 0 | 6. 5 I 8 2 | - 1 . 2 I 6.9 I 9 2 | - 3 . 9 J 6.7 I Age 2 Sn. 1 I - 12 . 4 J 4.9 1 3 1 | -30.1 | 3.9 I 4 1 | - 11 . 2 i 3. 7 I 5 1 | 1.3 I 4.3 | 6 1 1 10.2 | 4.3 I 7 1 | 8.4 J 4. 7 I 8 1 | 2.5 | 4. 9 I 9 1 J 12.2 | 5. 0 | Yr. 1 Sn. 1 | 21.7 | 3.6 I 2 1 I - 4 . 3 I 2. ? Overall Means For Dependent Variable least-Sguare = 1019.4 Arithmetic = 1004.5 131 least sguares constants for each freedom f i t t e d in- the analysis f o r summer change i n weight in 1974 & 1975 Subclass I L . S. Constant j S. E. Herd 1 J -0.19 | 0. 95 2 I 7.72 | 1. 02 3 | 3.00 | 1. 05 4 I -5.47 J 1. 56 Age 2 i 6.24 j 1. 94 3 I 5.12 | 1. 10 4 I 1.81 i 1.31 5 I -0.30 I 1. 08 6 J -0.71 I 1. 26 1 1 -0.32 | 1.70 8 i -2.36 | 1. 83 9 1 -5.26 ! 1.34 Year 1 | 5.68 | 0. 46 J (1)steer c a l f | 0.39 | 0. 33 j Hd. 1 Sex T— 1 | -0.16 j 0. 45 2 1 i -0.71 | 0. 49 3 1 i 0. 16 | 0. 60 4 1 i 1.44 | 0. 86 ! Hd. 2 Age 2 I 1.21 | 2. 63 3 2 i -1.14 j 3. 01 1 3 I -1.22 | 1. 52 2 3 | 0.70 | 1. 94 3 3 I -0.17 | 2. 59 4 3 I -1.44 | 1. 73 1 4 I 1.31 | 2. 15 2 4 I -1.11 | 2. 01 3 4 ! -2.24 | 2. 67 4 4 I -1.49 | 2. 51 1 5 I -3.98 | 1. 91 I 2 5 I -4.32 | 2. 37 J 3 5 I 3.93 | 2. 51 1 — 1 6 2 6 3 6 4 6 1 7 2 7 3 7 7 1 8 2 8 3 8 8 1 9 2 9 3 9 9 I Age 2 <| 3 1 4 1 5 1 6 1 7 1 8 1 .9 1 1 Age 2 Sex 1 3 1 4 1 5 1 6 1 7 1 8 1 a. 9 1 4,17 -0. 19 •3.08 •0.90 •0.69 •2. 16 0.75 1.01 •0.15 •0.33 •G.69 2.47 2. 12 5.73 •1.03 •5.58 •2.07 •0.75 •1.27 •1.57 2.25 •0. 89 0, 82 2.36 0. 22 0.28 •0. 19 0.07 0.52 •0.66 0.45 •0.90 2. 28 2. 44 2. 39 2. 0 9 2. 30 3. 30 2. 30 4. 02 3.24 3. 42 3. 19 4. 17 2. 39 2. 34 2. 81 2. 30 1. 01 0. 94 1. 06 1. 19 1. 56 1. 91 1. 22 0. 78 0. 78 0. 57 0. 63 0. 83 0. 79 0. 77 0. 92 0. 79 Overall Means For Dependent Variable Least-Sguare = 7.26 Arithmetic = 9.85 133 Least squares constants for each•degree•of•freedom f i t t e d in i k i analysis for summer change i n weight for 74 o-aly. Subclass L. S. Constant —+• Herd 1 3 4 8 Age (1)steer c a l f H - 9 . 6 8 1 4 . 7 7 - 5 . 3 5 3 . 2 9 0 . 0 9 + 2 i 3 . 42 1 1. 24 3 1 4 . 5 0 I 0 . 9 8 4 1 2 . 04 j 1 . 0 9 5 ! - 2 . 0 7 I 0 . 9 8 6 1 2 . 0 9 i 1. 27 7 1 - 0 , 5 6 I 1 .31 8 1 - 0 . 2 6 J 1. 54 9 1 - 4 . 6 9 I 1 . 7 6 S* IJ -m 0 . 91 0 . 9 8 0 . 9 5 1. 0 8 0 40 1 Age 2 j 0 . 1 8 I 1 . 7 9 3 2 ! - 1 . 6 8 1 1. 74 4 2 J - 2 . 6 9 I 1. 6 5 8 2 i • 3 . 9 8 I 2. 2 6 1 i 3 i 2 . 6 3 i 1 . 6 0 3 3 1 1 . 3 3 i 2 , 2 3 4 3 1 0 . 3 8 j 1. 8 2 8 3 1 - 1 . 8 3 i 2 . 0 3 1 I 1 \ - 2 . 1 2 i 1 . 8 8 3 n 1 5 . 0 9 I 2 , 11 4 4 1 0 . 4 7 | 2 , 4 8 8 4 1 • - 5 , 0 7 1 2 . 4 7 1 1 5 j - 1 . 9 8 [ 1. 8 8 3 5 I - 0 . 7 4 I 2 . 24 4 5 J - 0 . 3 6 i 2 . 19 8 5 I i - 0 . 8 0 j 1 . 6 5 1 1 6 | 7 . 9 5 I 2 . 64 3 6 1 - 3 . 9 2 i 1 . 9 9 4 6 1 - 1 . 6 6 I 2 . 15 8 6 I - 4 . 2 9 i 2 . 0 1 r 1  ~ s — -1 1 7 j - 0 . 53 | 1.94 3 7 | - 4 . 36 I 1.77 4 7 J - 1 .65 I 2. 58 8 7 J 6. 68 I 3. 11 1 8 ] - 4 . 87 I 2. 14 3 8 j 0.26 I 2. 16 4 8 j 4.52 I 5. 03 8 8 I 0.88 I 2. 41 1 9 s - 0 . 7 9 | 2. 23 3 9 I 4.61 I 2. 76 4 9 J -3 .41 I 2. 38 8 9 2. 19 | 5. 0 8 1 Age 2 Sex 1 j - 0 . 85 j 0.85 3 1 j 0.95 I 0.92 4 1 J - 1 . 44 J 1. 18 5 1 j 0.99 | 0. 94 6 1 j 1.74 I 1. 20 7 1 J - 0 . 39 I 1.04 8 1 j 0.70 I 1. 11 9 1 I -2 .11 I 1.33 ] Hd. 1 Sex 1 I 0.99 | 0.68 3 1 j 0.26 j 0. 71 4 1 j 0.29 I 0. 74 8 1 - 0 . 92 I 0. 79 t Overall Means .For Dependent Variable least-Sguare = 14.70 Arithmetic = 14.68 1 3 5 i f J l s t Squares constants for each degree of f reed-am fi£te<I i n the analysis for winter weight change | Subclass | L.S. Constant | S.E. | j .( +  I Herd 2 I - 0 . 4 8 I 0 . 4 8 | J 7 | - 2 . 0 5 | 0 . 7 4 | j Year 1 I 0 . 3 8 I 0 . 4 2 j I + + i | age 2 | 3 . 6 0 I 1. 2 5 J | 3 I 1 . 7 0 | 1 . 3 7 J | 4 | - 0 . 7 4 | 0 . 8 8 J I 5 1 0 . 3 9 J 0 . 8 2 J 1 6 | - 1 . 0 6 | 1 . 1 5 | J 7 | - 1 . 5 6 | 1 . 0 1 i J 8 | - 2 . 1 4 | 1 . 2 4 J i 9 I - 0 . 5 8 J 1 .11 1 1 Hd. 2 Yr. 1 I - 0 . 3 6 | 0 . 7 9 I 1 7 1 J - 2 . 7 5 1 0 . 5 4 | | Hd. 2 Age 2 | 0 . 2 8 | 1 .81 | I 7 2 I 6 . 9 3 | 2 . 3 2 | I 2 3 I 1 . 2 9 | 1 . 3 4 | 1 7 3 | - 1 . 4 9 | 2 . 15 | I 2 4 | 1 . 0 4 | 1 .01 I I 7 4 | - 4 . 2 3 | 1 . 5 5 | I 2 5 | 1 . 1 4 J 0 . 9 1 | I 7 5 | - 2 . 7 6 J 1 . 3 7 | I 2 6 | 1 . 8 3 I 1 . 0 5 | j 7 6 J - 0 . 8 6 | 1 . 4 4 J I 2 7 J - 1 . 4 5 1 1. 3 5 | I 7 7 | 0 . 8 7 | 1 . 5 2 | I 2 8 | - 0 . 7 7 | 1 . 3 4 J I 7 8 J - 0 . 5 9 | 2. 3 9 J I 2 9 I - 1 . 1 8 | 1 . 4 2 | I 7 9 | 0 . 4 8 I 2 . 1 4 1 « ~ ; -I ', j J 136 2 Yr. 1 j -0. 46 I 1. 06 3 1 | -0. 08 | 0. 82 4 1 | 1.14 I 0. 71 5 1 J -1.65 I 0.65 6 1 | -1.28 I 1. 06 1 1 I -0.31 I 1.16 8 1 | 0. 50 J 0. 74 9 1 | 0.61 I 0. 86 i. J , 1 , 2l§£all Means For Dependent Variable Least-Sguare = -0.97 Arithmetic = 0.25 137 Least Sguares Constants For Each Degree Of Freedom P i t t e d In Analysis For Weights Considered. As Da xs Pregnant 1  1 Year 1 + — L.S. const Age 2 j -224.1 I 7. 2 3 I -97.8 I 4. 5 4 I -33. 3 I 7. 4 5 I -4.5 I 6. 4 6 I -0.4 I 6. 3 7 I 22.6 | 10. 7 3 I 85. 3 \ 7. 2 9 | 52.0 ) 8. 1 10 J 58.5 I 8. 4 11 j 72.5 I 8. 4 -26.0 Age 3 Yr. 1 I -3.1 I 4. 6 4 1 j 3.2 I 7. 3 5 1 I -16.5 I 6. 4 6 1 I 5.9 | 6. 3 7 1 I 1.4 I 10. 6 8 1 i 1. 1 I 7. 2 9 1 | 29.7 I 8. 1 10 1 I -10.9 I 8. 3 11 1 I -8.8 I 8. 4 — — ± _. S. E. 2. 6 Oyerall Mean For Dependent Variable Least-Sguare = 1131.8 Arithmetic = 1051.4 138 lPP:§J2dix 2 Weighing Dates 1973 1974 Herd F a l l Spring F a l l 1975 1976 Spring F a l l Spring 15/11 19/3 28/3 1/4 18/4 14/11 25/3 3/4 8/4 23/4 13/11 4/12 17/3 25/3 14/5 17/5 18/11 21/11 27/11 5/5 7/5 8/5 30/9 9/10 28/10 30/10 3/5 4/5 5/5 27/10 4/5 1/6 2/11 9/11 2/11 8/5 1/11 17/12 4/5 26/4 17/10 30/11 26/10 31/12 20/10 at b i r t h 11/6 15/6 1/10 at birth 30/10 12/6 17/5 17/10 10/12 2 0/4 9/5 27/4 28/4 29/4 8/11 9/11 1/5 30/10 13/10 31/3 20/4 13/4 18/10 17/4 

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