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The influence of early and late breeding of dairy cows on fertility, weight changes and on milk production.. 1980

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THE INFLUENCE OF EARLY AND LATE BREEDING OF DAIRY COWS ON FERTILITY, WEIGHT CHANGES AND ON MILK PRODUCTION OF THE PRESENT AND SUBSEQUENT LACTATION by FRITZ SCHNEIDER Dipl . Ing.-Agr. ETH 1977 Swiss Federal I n s t i t u t e of Technology A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF - MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Animal Science We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1980 © F r i t z Schneider, 1980 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of ANIMAL SCIENCE The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date JUNE 11 , 1980 - i i - ABSTRACT In a H o l s t e i n herd (125 cows) the i n f l u e n c e of e a r l y and l a t e breeding post partum on reproduction and production was i n v e s t i g a t e d . At c a l v i n g the cows were randomly assigned to two groups. The e a r l y bred group was scheduled to be bred at the f i r s t v i s i b l e heat f o l l o w i n g 50 days post partum which r e s u l t e d in an average i n t e r v a l of 73 ± 18 days from p a r t u r i t i o n to the f i r s t s e r v i c e . The average i n t e r v a l from p a r t u r i t i o n to conception was 88 ± 33 days. The cows in the e a r l y bred group conceived a f t e r an average of 1.50 (range: 1 to 3) se r v i c e s per conception. The l a t e bred group was scheduled to be bred at the f i r s t v i s i b l e heat f o l l o w i n g 80 days post partum which r e s u l t e d in an average i n t e r v a l of 93 ± 17 days from p a r t u r i t i o n to the f i r s t s e r v i c e . The average i n t e r v a l from p a r t u r i t i o n to conception was 120 ± 40 days. The cows in the l a t e bred group conceived a f t e r an average of 1.96 (range: 1 to 5) serv i c e s per conception. The number of serv i c e s per conception was s i g n i f i c a n t l y (P£.05) higher f o r the l a t e bred group. The e a r l y post partum reproductive a c t i v i t y was monitored with milk progesterone analyses. A sample of milk s t r i p p i n g s was analysed by a radioimmunoassay technique every second day from 6 days post partum u n t i l conception occurred or the animal was removed from the h e r d . C o w s w h i c h d i d n o t c o n c e i v e w e r e e x c l u d e d f r o m t h e s t a t i s t i c a l a n a l y s e s . T h e a v e r a g e l e n g t h o f t h e f i r s t e s t r o u s c y c l e w a s 17 ± 7.5 d a y s . T h e f i r s t p r o g e s t e r o n e d e t e c t e d h e a t o c c u r r e d 33 ± 10 d a y s p o s t p a r t u m c o m p a r e d t o t h e f i r s t v i s i b l e h e a t w h i c h o c c u r r e d 4 8 ± 2 6 d a y s p o s t p a r t u m . C a l v i n g a s s o c i a t e d p r o b l e m s a n d t h e c a l v i n g d u r i n g t h e p a s t u r e s e a s o n d e l a y e d c o n c e p t i o n i n t h e l a t e b r e d g r o u p b u t n o t i n t h e e a r l y b r e d g r o u p . T h e l a t e b r e d g r o u p p r o d u c e d m o r e f a t c o r r e c t e d m i l k ( F C M ) i n t h e 305 d a y l a c t a t i o n a n d i n t h e f i r s t 150 d a y s o f t h e s u b - s e q u e n t l a c t a t i o n a n d a l s o g a i n e d m o r e ( P ^ .05) w e i g h t b e t w e e n c a l v i n g s . C o w s c a l v i n g d u r i n g t h e p a s t u r e s e a s o n p r o d u c e d m o r e F C M i n t h e 305 d a y l a c t a t i o n b u t g a i n e d s i g n i f i c a n t l y (PJ6.01) l e s s w e i g h t b e t w e e n c a l v i n g s t h a n c o w s c a l v i n g i n t h e n o n - p a s t u r e s e a s o n . T h e r e w a s n o d i f f e r e n c e b e t w e e n e a r l y a n d l a t e b r e d g r o u p , h e a l t h s t a t u s g r o u p s o r g r o u p s a c c o r d i n g t o t h e c a l v i n g s e a s o n i n t e r m s o f a v e r a g e d a i l y m i l k a n d FCM y i e l d c a l c u l a t e d o v e r t h e e n t i r e p e r i o d o f t h i s e x p e r i m e n t ( b e g i n n i n g o f c u r r e n t l a c t a t i o n t o d a y 150 o f t h e s u b s e q u e n t l a c t a t i o n , i n c l u d i n g t h e d r y p e r i o d ) . C a l v i n g d i f f i c u l t i e s a n d e a r l y p o s t p a r t u m r e p r o d u c t i v e p r o b l e m s w e r e n o t r e l a t e d t o p r o d u c t i o n t r a i t s . - i V- T A B L E OF C O N T E N T S P a g e A b s t r a c t i i T a b l e o f C o n t e n t s i v L i s t o f T a b l e s v i i L i s t o f F i g u r e s x L i s t o f A p p e n d i x T a b l e s x i A c k n o w l e d g e m e n t s x i i 1 . I N T R O D U C T I O N 1 2 . L I T E R A T U R E R E V I E W 4 3 . M A T E R I A L AND M E T H O D S 1 5 3 . 1 . A n i m a l s 16 3 . 2 . M i l k s a m p l i n g a n d m i l k p r o g e s t e r o n e a n a l y s e s . 17 3 . 3 . V i s u a l h e a t d e t e c t i o n 1 8 3 . 4 . D a t a c o l 1 e c t i o n 1 8 3 . 5 . E x p e r i m e n t a l d e s i g n a n d s t a t i s t i c a l a n a l y s i s . 19 3 . 5 . 1 . L a c t a t i o n c u r v e c o m p u t a t i o n 1 9 3 . 5 . 2 . A n a l y s i s o f v a r i a n c e ( A N O V A ) m o d e l . 2 0 3 . 5 . 3 . T e s t o f i n f l u e n c e o f d a y s o p e n o n p r o d u c t i o n i n s u b s e q u e n t l a c t a t i o n . 2 4 3 . 5 . 4 . C o r r e l a t i o n c o e f f i c i e n t s 2 4 4 . R E S U L T S 2 5 4 . 1 . T e s t f o r b i a s i n t h e g r o u p s 2 5 4 . 2 . R e p r o d u c t i v e t r a i t s 27 4 . 2 . 1 . I n f l u e n c e o f e a r l y v e r s u s l a t e b r e e d i n g 2 9 4 . 2 . 2 . I n f l u e n c e o f t h e h e a l t h 31 - y T P a g e 4 . 2 . 3 . I n f l u e n c e o f c a l v i n g s e a s o n 3 3 4 . 2 . 4 . I n t e r a c t i o n s 3 3 4 . 3 . B o d y w e i g h t s a n d b o d y w e i g h t c h a n g e s i n t h e c u r r e n t l a c t a t i o n 3 9 4 . 3 . 1 . I n f l u e n c e o f e a r l y v e r s u s l a t e b r e e d i n g 3 9 4 . 3 . 2 . I n f l u e n c e o f h e a l t h 41 4 . 3 . 3 . I n f l u e n c e o f s e a s o n 4 4 4 . 4 . P r o d u c t i v e t r a i t s i n t h e c u r r e n t l a c t a t i o n . . 4 6 4 . 4 . 1 . I n f l u e n c e o f e a r l y v e r s u s l a t e b r e e d i n g 4 6 4 . 4 . 2 . I n f l u e n c e o f h e a l t h 4 9 4 . 4 . 3 . I n f l u e n c e o f s e a s o n 4 9 4 . 5 . C a r r y - o v e r e f f e c t s f r o m t h e c u r r e n t t o t h e s u b s e q u e n t l a c t a t i o n 5 2 4 . 5 . 1 . I n f l u e n c e o f e a r l y v e r s u s l a t e b r e e d i n g 5 2 4 . 5 . 2 . I n f l u e n c e o f h e a l t h 5 5 4 . 5 . 3 . I n f l u e n c e o f s e a s o n 57 4 . 6 . A v e r a g e d a i l y m i l k p r o d u c t i o n o v e r t h e t w o l a c t a t i o n s 5 9 4 . 7 . C o r r e l a t i o n s a n d r e g r e s s i o n s 61 4 . 7 . 1 . C o r r e l a t i o n s b e t w e e n r e p r o d u c t i v e t r a i t s 61 4 . 7 . 2 . C o r r e l a t i o n s b e t w e e n r e p r o d u c t i v e a n d p r o d u c t i v e t r a i t s o f t h e c u r r e n t l a c t a t i o n 6 3 4 . 7 . 3 . C o r r e l a t i o n s b e t w e e n r e p r o d u c t i v e t r a i t s o f t h e c u r r e n t a n d p r o d u c t i v e t r a i t s o f t h e s u b s e q u e n t l a c t a t i o n . 6 3 - v i - Page '4.7.4. C o r r e l a t i o n s between reproductive t r a i t s and body weight changes in the current and subsequent l a c t a t i o n 65 4.7.5. Test of influ e n c e of days open on production in the subsequent 1 a c t a t i on 67 5. DISCUSSION 69 5 . 1 . Onset of the estrous c y c l e v i s u a l and progest- erone detected heats 69 5.2. Days from p a r t u r i t i o n to the f i r s t s e r v i c e to conception and to the next c a l v i n g 72 5.3. The r e l a t i o n s h i p between reproduction, production and body weight changes 76 6. SUMMARY AND CONCLUSIONS 83 7. BIBLIOGRAPHY 86 8. APPENDIX 93 - v i i - LIST OF TABLES Table _page 1 Reasons for c u l l i n g of the cows from the herd during the experiment 16 2 Number of observations 21 3 Means and standard deviations of t r a i t s at the time of c a l v i n g and in the e a r l y post partum period . . . . 26 4 Means and standard d e v i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between the e a r l y bred and the l a t e bred group 30 5 Means and standard de v i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between the two health codes . . 32 6 Means and standard de v i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between pasture season and non- pasture season 34 7 I n t e r a c t i o n s between groups, health codes and seasons in reproductive t r a i t s 36 8 S i g n i f i c a n t group-health code i n t e r a c t i o n s in reproductive t r a i t s . A n a l y s i s w i t h i n the e a r l y bred broup 36 9 S i g n i f i c a n t group-health code i n t e r a c t i o n s in reproductive t r a i t s . A n a l y s i s w i t h i n the l a t e bred group . 37 10 S i g n i f i c a n t group-season i n t e r a c t i o n s i n reproductive t r a i t s . A n alysis w i t h i n the e a r l y bred group 37 11 S i g n i f i c a n t group-season i n t e r a c t i o n s in reproductive t r a i t s . A n a l y s i s w i t h i n the l a t e bred group 38 12 S i g n i f i c a n t sea son-health code i n t e r a c t i o n s f o r the ca l v i n g i n t e r v a l . A n a l y s i s w i t h i n seasons 38 13 Means and standard d e v i a t i o n s of body weights and body weight changes in the current l a c t a t i o n and at the subsequent c a l v i n g . The d i f f e r e n c e s between ea r l y bred and l a t e bred group 40 14 Sex of calves 42 - v i i i - Table Page 15 Group health status i n t e r a c t i o n f o r body weight gain (kg) between c a l v i n g s . The a n a l y s i s w i t h i n breeding groups 42 16 Means and standard d e v i a t i o n s of body weights and body weight changes i n the current l a c t a t i o n and at the subsequent c a l v i n g . The d i f f e r e n c e s between heal th codes . . . .43 17 Means and standard d e v i a t i o n s of body weight and body weight changes in the current l a c t a t i o n and at the subsequent c a l v i n g . The d i f f e r e n c e s between calvings during the pasture season and non-pasture season 45 18 Means and standard deviations of p r o d u c t i v e * t r a i t s in the current l a c t a t i o n and the' d i f f e r e n c e s between * e a r l y bred and,late bred group 4Z 19 Means and standard d e v i a t i o n s of t r a i t s in the subsequent l a c t a t i o n and the d i f f e r e n c e s between ea r l y bred and l a t e bred group 53 20 Means and standard d e v i a t i o n s of t r a i t s in the subsequent l a c t a t i o n and the d i f f e r e n c e s between the health code groups (health codes of the current l a c t a t i o n ) 55 21 Means and standard deviations of t r a i t s i n the subsequent l a c t a t i o n i nfluenced by the c a l v i n g season of the current l a c t a t i o n 57 22 Average d a i l y milk and FCM production from the beginning of the current l a c t a t i o n to day 150 of the subsequent l a c t a t i o n 60 23 C o r r e l a t i o n s between reproductive t r a i t s of the current post partum period 62 24 C o r r e l a t i o n s between reproductive and productive t r a i t s of the current l a c t a t i o n 62 25 C o r r e l a t i o n s between reproductive t r a i t s of the current and productive t r a i t s of the subsequent l a c t a t i o n 64 - i x - Table Page 26 C o r r e l a t i o n s between reproductive t r a i t s and body weight changes in the current and subsequent l a c t a t i o n 66 27 Results of the simple regression analyses with days open as independent continuous v a r i a b l e 68 - x - LIST OF FIGURES- Figure Page 1 D e f i n i t i o n s of the f i r s t estrous c y c l e length and the f i r s t progesterone detected heat on the base of milk progesterone l e v e l s in the e a r l y post partum period 28 2 Mean production and slopes of e a r l y and l a t e bred group f o r f a t %, milk and f a t corrected milk on the current l a c t a t i o n 48 3 Mean production and slopes of health code group 1 and health code group 2 f o r f a t %, milk and f a t corrected milk of the current l a c t a t i o n 50 4 Mean production and slopes of cows c a l v i n g during the pasture season versus the non-pasture season fo r f a t %, milk and f a t corrected milk of the current l a c t a t i o n 51 5 Mean production and slopes of e a r l y and l a t e bred group f o r f a t %, milk and f a t corrected milk of the subsequent l a c t a t i o n (0-150 days) 54 6 Mean production and slopes of health code group 1 and health code group 2 for f a t %, milk and f a t corrected milk of the subsequent l a c t a t i o n 56 7 Mean production and slopes of f a t %, milk and f a t corrected milk of the subsequent l a c t a t i o n (0- 150 days). Differences due to the c a l v i n g season of the current l a c t a t i o n 58 - x i - L I S T OF A P P E N D I X T A B L E S Table Page .1 Means and standard d e v i a t i o n s of the co v a r i a b l e s milk production 0-50 days post partum, body weight changes 0-60 days post partum in the current l a c t a t i o n and age of c a l v i n g at the beginning of the current l a c t a t i o n 93 2 Means and standard d e v i a t i o n s of reproductive t r a i t s in the current l a c t a t i o n 94 3 Means and standard d e v i a t i o n s of productive t r a i t s in the current l a c t a t i o n 95 4 Means and standard d e v i a t i o n s of body weights and body weight changes in the current l a c t a t i o n and at the subsequent c a l v i n g 96 5 Means and standard d e v i a t i o n s f o r t r a i t s in the subsequent l a c t a t i o n 97 6 C o r r e l a t i o n s between the body weight and the body weight changes in the current l a c t a t i o n 98 7 C o r r e l a t i o n s between body weight and body weight changes in the subsequent l a c t a t i o n 98 8 C o r r e l a t i o n s between body weight and body weight changes and milk production in the current l a c t a t i o n . 99 9 C o r r e l a t i o n s between body weight and body weight changes and milk production in the subsequent 1 a c t a t i on 99 - x i i - ACKNOWLEDGEMENTS The author would l i k e to take t h i s opportunity to acknowledge the e f f o r t s of those people who were of prime importance to the research and preparation of t h i s t h e s i s . Special thanks to Dr. J.A. S h e l f o r d , Department of Animal Science U.B.C., under whose su p e r v i s i o n t h i s work was done and whose pat i e n t assistance i s g r e a t l y appreciated. Many thanks to Dr. L.J. F i s h e r , Research S t a t i o n , Agassiz f o r the permission to use the data of the dairy herd of the Research S t a t i o n and his advice and suggestions. The author also wishes to acknowledge the help of Dr. R.G. Peterson and Mrs. M. S t r i k e r f o r t h e i r i n v a l u a b l e advice and assistance in the a n a l y s i s of the data. Thank you also to the technicians in the Department of Animal Science U.B.C. f o r the a n a l y s i s of the milk samples. Thanks are also due to the So c i a l Sciences and Humanities Research Council of Canada f o r the awards which enabled the author to study in Canada. - 1 - 1. INTRODUCTION Milk y i e l d and reproductive performance are two very important f a c t o r s determining the p r o f i t a b i l i t y of a dai r y herd. On many dair y farms reproduction does not fol l o w an optimum course. Therefore, i t i s important that reproductive problems are traced to t h e i r source as r a p i d l y and e f f i c i e n t l y as p o s s i b l e . Impaired reproduction r e s u l t s i n a decreased pro- duction per day of l i f e and therefore higher production costs. I t i s e s s e n t i a l to analyse and explain as many fa c t o r s associated with reproductive f a i l u r e as pos s i b l e and to quantify the in f l u e n c e s on production. A widely used measure of f e r t i l i t y i s the c a l v i n g i n t e r v a l . A c a l v i n g i n t e r v a l of 12 to 13 months i s thought to be ideal and i s pos s i b l e i f the s e r v i c e period i s kept w i t h i n 60 to 90 days post partum. From the p h y s i o l o g i c a l point of view, a one year c a l v i n g i n t e r v a l i s f e a s i b l e 3 however , c a l v i n g d i f f i c u l t i e s , r e t a i n e d placentas, e n d o m e t r i t i s , veneral i n f e c t i o n s , s i l e n t heats, etc. delay conception and make an optimum c a l v i n g i n t e r v a l d i f f i c u l t to a t t a i n . One step toward reducing the c a l v i n g i n t e r v a l i s to use milk progesterone to c h a r a c t e r i z e estrous cycles and to i d e n t i f y non- pregnant cows as e a r l y as p o s s i b l e . The milk progesterone concentration changes during the course of the estrous - 2 - c y c l e , being low ( 2ng/ml) during standing heat and markedly higher (>5ng/ml) between heats. The milk pro- gesterone concentration can be determined by a rapid radioimmunoassay technique which makes i t p o s s i b l e to use progesterone l e v e l s in milk to monitor estrous cycles in d a i r y cows. Milk progesterone analyses are widely used in Europe and North America (Heap et a l . , 1 973 ; Hoffmann et al . , 1 976 ; Shelford et al . , 1 979) to monitor estrous c y c l e s , to e s t a b l i s h the reproductive status of problem cows and f o r an e a r l y pregnancy check. The purpose of the study herein was to e s t a b l i s h the occurrence of the f i r s t hormonal estrous cycle and the f i r s t hormonal estrus with milk progesterone analyses and to compare the r e s u l t s with the v i s u a l l y detected heats. Reproductive data and productive data were analysed in r e l a t i o n to s p e c i f i c breeding times post partum, to days open and to the c a l v i n g i n t e r v a l . The i n f l u e n c e of c a l v i n g associated reproductive problems and the i n f l u e n c e of the c a l v i n g season on reproductive and productive performance of the current l a c t a t i o n and on productive performance of the subsequent l a c t a t i o n was i n v e s t i g a t e d . The o b j e c t i v e s of t h i s study were: To compare v i s u a l l y detected heats with milk progesterone detected estrus and to t e s t whether the onset of estrus was influenced by the c a l v i n g season, c a l v i n g associated reproductive - 3 - problems and the l e v e l of production. To i n v e s t i g a t e the i n f l u e n c e of e a r l y and l a t e breeding, the i n f l u e n c e of c a l v i n g associated problems and the in f l u e n c e of the c a l v i n g season on the reproductive performance in the current l a c t a t i o n and the productive performance i n the current and e a r l y subsequent l a c t a t i o n . - 4 - 2. LITERATURE REVIEW I n e f f i c i e n t reproductive performance i s known as one of the major herd management problems (Rounsaville et al . , 1 979 ; Spalding et al . , 1 975 ). Larger herds and increased mechanization r e s u l t in less time spent per cow and can lead to decreasing reproductive success i f the management s k i l l s and record keeping are not strengthened. The reproductive process i s very complex and very d i f f i c u l t to understand f u l l y . A great number of studies have been and s t i l l are being conducted dealing mostly with one or a few of the reproductive aspects or productive-repro- ductive r e l a t i o n s h i p s . The purpose of the f o l l o w i n g part of t h i s study i s to review some of the most important information and r e s u l t s . Age of Cow. The age of the cow has a marked e f f e c t on the pregnancy rate a f t e r the f i r s t insemination (Boyd and Reed, 1961; De K r u i f , 1 975 ; Rosenberg et a l . . , 1 977 ). Most i n v e s t i g a t o r s conclude that the pregnancy rate i s reduced in animals which have calved for the f i r s t time. De K r u i f (1975) observed a d i f f e r e n c e of 5% in the pregnancy rate between primiparous and secundiparous cows. In cows 7 years and older the conception rate a f t e r the f i r s t insemination i s also low. Flores (1972) and De K r u i f (1975) report that primiparous cows have more days open than multiparous cows. They do not a t t r i b u t e the reduced - 5 - conception rate i n primi parous cows to t h e i r age as such, but to the f a c t that problems associated with c a l v i n g are more l i k e l y to occur at the f i r s t c a l v i n g and during the f i r s t post partum period. De K r u i f (1975) showed that these d i f f e r e n c e s disappeared when he removed a l l the primiparous cows which had some problems associated with c a l v i n g . Wilton et al . ( 1 967 ) did not f i n d any influence of age on the i n t e r v a l from c a l v i n g to con- ception. Health of cow. I n f e c t i o n s caused by V i b r i o f e t u s , Tri chomonas f e t u s , B r u c e l l a abortus, Leptospiroa, etc. d i s t u r b the f e r t i l i t y of dairy c a t t l e a great deal. Several of these diseases, .however, are under c o n t r o l , at l e a s t in the i n d u s t r i a l i z e d c o u n t r i e s . Beside these i n f e c t i o u s diseases there are a number of non-infectious disturbances l i k e r etained placentas, trauma to repro- ductive t r a c t and uterine i n e r t i a . These disturbances can i n f l u e n c e the reproductive performance of a dairy herd very d r a s t i c a l l y . Roberts (1971) and De K r u i f (1978) r e l a t e d part of these disturbances to inadequate hygiene, e s p e c i a l l y at the time of c a l v i n g . Retained placenta and endometritis are known to reduce the f e r t i 1 i t y • b y - 5 to 10% at the f i r s t insemination r e s u l t i n g in more days open (Dyrendahl et a l . , 1 976 ; Morrow et a l . , 1 969 ; Roine and Saloniemi, 1978; Zamet et a l . , 1979). De K r u i f (1975) stressed the f a c t that c a l v i n g hygiene i s p a r t i c u l a r l y - 6 - important in loose housing systems where cows come i n t o c l o s e r and more frequent contact with other cows than in stanchion barns, r e s u l t i n g in an increased r i s k of i n f e c t i o n . Climate and season. The climate i s an important f a c t o r a l t e r i n g conception rate in c a t t l e (Thatcher, 1974). High temperatures and humidity w i l l depress behavioural estrus signs and with i t the conception r a t e . Early embryonic death i s believed to occur more often in the t r o p i c s than in temperate regions ( S t o t t and W i l l i a m s , 1962). High ambient temperatures i n f l u e n c e the plasma progesterone l e v e l r e s u l t i n g in a decreased conception rate (Rosenberg et a l . , 1 977 ; Roussel et al . , 1 977 ). Season has a very d e f i n i t e i n f l u e n c e on f e r t i l i t y in dai r y c a t t l e . In temperate regions, pregnancy rates are highest in spring ( M i l l e r et a l . , 1 970a; De K r u i f , 1 975 ) and are depressed during the winter months. The plasma progesterone l e v e l s during estrus are lower in wintertime which i s favourable f o r conception (Roussel et al . , 1 977 ), but the heat detection as such i s poorer due to constant confine- ment of the cows and less d a y l i g h t in the barns (David et a l . , 1971; King et a l . , 1 976 ). David et al . (1971) and Mather et a l . (1978) found that l i t t l e behavioural evidence i s shown with the f i r s t e s t r u s . During the pasture season estrus behaviour i s much stronger and more evident for v i s u a l d e t e c t i o n . Francos et al . ( 1 977) found that the - 7 - voluntary feed intake in summer i s s i g n i f i c a n t l y higher than in winter and they also r e l a t e d these f i n d i n g s and the increased exercise im summer to f e r t i l i t y as w e l l . ' Body weight change patterns. The body weight change pattern of dair y cows and i t s r e l a t i o n to f e r t i l i t y has been studied by many authors (Amir and K a l i , 1974; Huth and Smidt, 1 979 ; M i l l e r and Hooven, 1 970b; Touchberry and. Batra, 1976; Youdan and King, 1977). The high e a r l y l a c t a t i o n milk production requires n u t r i e n t s in excess of the d i e t a r y intake of the cow. Therefore, the cow s t a r t s to mobilize body reserves and consequently loses weight in the f i r s t part (up to 50 to 70 days post partum) of the l a c t a t i o n (Amir and K a l i , 1974; M i l l e r and Hooven, 1970b; Youdan and King, 1977). This weight loss i s dependent on many f a c t o r s ; l e v e l of milk production, milk composition, plane of n u t r i t i o n , and the protein-energy r e l a t i o n s h i p of the d i e t being only a few of them ( B r o s t e r , 1973). There i s evidence in the l i t e r a t u r e (King et al . , 1 976 ; Youdan and King, 1977) that cows which are gaining weight during the time of insemination have a better rate of conception than cows l o s i n g weight. Boyd (1970) demonstrated a b e n e f i c i a l e f f e c t of body weight gain on f e r t i l i t y rate but his r e s u l t s were not s t a t i s t i c a l l y s i g n i f i c a n t . This f i n d i n g i n d i c a t e d that e a r l y post partum breeding ( f i r s t s e r v i c e before 60 days post partum) r e s u l t e d in an i n f e r i o r rate of conception compared to insemination a f t e r a - 8 - longer r e s t period. Herz and Graf (1976) and Roberts et al . ( 1 979a) r e l a t e d the d i f f i c u l t i e s of g e t t i n g cows pregnant with weight loss or low blood glucose l e v e l s at the time of insemination. Blood glucose l e v e l s were lower in the e a r l y post partum period than in the l a t e pre-partum and l a t e r post partum period. Roberts et al . (1979b) r e l a t e d t h e i r f i n d i n g s to the m o b i l i z a t i o n of adipose t i s s u e due to a lack of s u f f i c i e n t d i e t a r y energy intake. Time from p a r t u r i t i o n to f i r s t insemination. The dis c u s s i o n of the e a r l y l a c t a t i o n weight changes leads d i r e c t l y to the dis c u s s i o n of the optimal r e s t period. I f we are di s c u s s i n g t h i s subject we have to s p e c i f y whether we are aiming f o r a high conception rate at the f i r s t insemination post partum, a short i n t e r v a l from c a l v i n g to conception, a maximum l a c t a t i o n milk y i e l d or a maximum l i f e time production. The conception rate i s reported to be low i n cows inseminated p r i o r to 50 days post partum ( B r i t t , 1 975 ; Shannon et al . , 1 952 ; Touchberry.et. a l . , 1 959 ; Whitmore et a l . , 1974). I t i s gene r a l l y accepted that a c a l v i n g i n t e r v a l of 12 months i s a d e s i r a b l e goal (Ayalon et a l . , 1971; B r i t t , 1975). The 12 month c a l v i n g i n t e r v a l i s even agreed upon by such a strong c r i t i c of ea r l y s e r v i c e a f t e r c a l v i n g as Dawson (1967). Louca and Legates (1968) propose a c a l v i n g i n t e r v a l of 13 months f o r p r i m i - parous cows and 12 months f o r multiparous cows in order - 9 - to a t t a i n maximum production. Cows must conceive on the average by about 85 days post partum to a t t a i n a 12 month c a l v i n g i n t e r v a l . Therefore, i t i s necessary to s t a r t insemination p r i o r to 60 days post partum f o r the simple reason that under the best c o n d i t i o n s cows vary i n the date of appearance of heat and waiting 60 days before breedings r e s u l t s i n an average c a l v i n g to f i r s t s e r v i c e i n t e r v a l much longer than 60 days (Ayalon et al . , 1971). Furthermore, as discussed p r e v i o u s l y , e a r l y post partum breeding r e s u l t s in lower conception rates which underlines the necessity to s t a r t breeding e a r l y i n order to obtain a short average c a l v i n g i n t e r v a l . The r e l a t i o n s h i p between time of breeding post partum and milk production has been discussed repeatedly through- out the years (Bar-Anan and S o l l e r , 1979; Boyd, 1970; Louca and Legates, 1968; Smith and Legates, 1962; Trim- berger, 1 954 ; Whitmore et a l . , 1 974 ; Wilton et al . , 1 967 ). Trimberger (1954) considered e a r l y breeding as a d i s - advantage, e s p e c i a l l y for show c a t t l e , because the i l a c t a t i o n milk y i e l d decreases i f cows are bred e a r l y a f t e r p a r t u r i t i o n . Louca and Legates (1968) stated that from the economical standpoint the y i e l d per uni t time, milk per day or year i s more important than the t o t a l l a c t a t i o n production. Ripley et a l . (1970) suggested the i n c l u s i o n of days open into the performance record of d a i r y cows. B r i t t (1975) showed c l e a r l y that the milk - 10 - production per day of l i f e i s highest in cows with short c a l v i n g i n t e r v a l s . Menge et a l . (1962) and Smith and Legates (1962) reported on the basis of t h e i r l i t e r a t u r e reviews that the opinion that high producing cows do not conceive as r e a d i l y as low producers, lacks conclusive experimental evidence. Ayalon et a l . (1971) reported that high producing cows react favourably to a r e s t period of 60 days and that there are ho reasons why moderate pro- ducing cows of good general and reproductive health should ! n o t be bred at the f i r s t estrus a f t e r 45 days post partum. Whitmore et a l . (1974) found that e a r l y breeding of high producing cows did not in f l u e n c e the success of sub- sequent inseminations. Francos and Rattner (1975) compared the c a l v i n g to conception i n t e r v a l of high producing cows with t h e i r milk y i e l d . A l l the cows were inseminated at the f i r s t estrus a f t e r 60 days post partum. They found that cows y i e l d i n g 8000 kg or more in a 305 day l a c t a t i o n on an average did not conceive before 110 days post partum. Herz et a l . (1979) i n v e s t i g a t e d the production of return and non-return cows and found a s i g n i f i c a n t l y higher production both in milk y i e l d and f a t corrected milk y i e l d of the return cows. Neither Francos and Rattner ( 1 975 ) nor Herz et al . ( 1 979) were able to determine whether the return cows did not conceive a f t e r the f i r s t insemination because they produced more milk or whether they produced more milk because they did not conceive - 11 - r e a d i l y . Bar-Anan and S o l l e r (1979), in t h e i r study on the e f f e c t s of days open on milk y i e l d , d e f i n i t e l y r e j e c t e d the accepted 305 day l a c t a t i o n y i e l d as an unbiased estimate of the production a b i l i t y . They found that the 305 day records penalize cows which conceive e a r l y . For t h i s reason, I s r a e l introduced a system which adjusts l a c t a t i o n milk y i e l d f o r days open as proposed e a r l i e r by Ripley et al . ( 1 970 ) . Heat d e t e c t i o n . In order to breed the cows f o r a shorter c a l v i n g i n t e r v a l , i t i s e s s e n t i a l to employ a systematic and e f f i c i e n t method of estrus d e t e c t i o n . The l a r g e r the herds and the more mechanized the whole operation becomes, the more important i t i s to use a systematic estrus detection method. While an unsystematic observation technique might be appropriate in small herds, t h i s technique becomes i n e f f i c i e n t with l a r g e r herds. So f a r , there i s no technique as good and e f f i c i e n t as a systematic observation of the herd. Problems of estrus detection occur e s p e c i a l l y in the e a r l y post partum period because signs of estrus are not as obvious as l a t e r on. David et a l . (1971) reported that 60% of a l l f i r s t heats remain undetected because the cows are not c o n t r o l l e d and observed properly. P e l i s s i e r (1976) found that heat detection f a i l u r e in C a l i f o r n i a was the primary cause of delayed f i r s t s e r v i c e and also contributed s i g n i f i c a n t l y to the delay of the subsequent s e r v i c e s . There i s a - 12 - considerable amount of information a v a i l a b l e on heat detection methods and heat detection a i d s . Gartland et al . ( 1 976 ) measured the vaginal mucus e l e c t r i c a l l y . Kiddy (1977) tested the use of a pedometer to measure the a c t i v i t y of the cow and found a f o u r f o l d increase in the a c t i v i t y of cows in e s t r u s . The f o u r f o l d increase was observed in a loose housing system. A c t i v i t y increases in stanchion barns as well but l e s s than in free s t a l l s . Foote (1975) described a whole range of mechanical heat detection aids (video camera and cow or b u l l mounted detectors and markers). Heat detection aids which require a teaser or gomer b u l l are quite expensive and s t i l l r equire a f a i r amount of labour to obtain s a t i s f a c t o r y r e s u l t s . Foote (1975) commented: "There i s no s u b s t i t u t e f o r the eye of the s k i l l e d observer and manager who observes his cows fo r e s t r u s . " Plasma and milk progesterone a n a l y s i s . Since the development of radioimmunoassay techniques (RIA), progesterone l e v e l s have become one of the major hormonal parameters used to monitor reproductive performance in c a t t l e . Measurements of progesterone in plasma have been made for a number of years (Stabenfeldt et a l . , 1961). Robertson and Sarda (1971) f i r s t used t h i s method to diagnose pregnancy in several domestic species. Laing and Heap (1971) found that progesterone in the milk of cows was c l o s e l y c o r r e l a t e d with the a c t i v i t y of the - 13 - corpus luteum and, t h e r e f o r e , suggested i t be used as an i n d i c a t o r f o r pregnancy. Hoffmann and Hamburger (1973) described the pattern of milk progesterone throughout the estrous cycle and the increase i n progesterone con- c e n t r a t i o n i n e a r l y pregnancy. During standing heat the milk progesterone concentration i s very low and r i s e s from about the 3rd to 4th day a f t e r standing heat reaching a peak between the 12th and 16th day. The concentration drops again around days 17 to 20 of the 21-day cycle (Booth, 1979). The development of a rapid radioimmunoassay technique (Heap et a l . , 1973; Heap et a l . , 1976) made i t possible to use milk progesterone l e v e l s f o r commercial pregnancy t e s t i n g (Booth and Holdsworth, 1976), f o r confirmation of estrus (Hoffmann et a l . , 1 976 ) and f o r monitoring the estrous cycle of s u b - f e r t i l e cows (Lamming and Bulman, 1976; Braun, 1977). The milk progesterone l e v e l s are hig h l y c o r r e l a t e d with the f a t content of the milk. In order to obtain r e l i a b l e r e s u l t s , i t i s important that one milk sampling method i s used c o n s i s t e n t l y . Shelford et al . ( 1 979) recommended the use of the milk s t r i p p i n g s , Braun ( 1 977 ) corrected the samples.;to 10% milk f a t and Hoffmann et a l . (1977) recommended the a n a l y s i s of the progesterone l e v e l i n samples of milk f a t only. - 14 - The milk progesterone radioimmunoassay i s i n c r e a s i n being used to a s s i s t the management of dai r y herds in accomplishing a high l e v e l of f e r t i l i t y . I t represents a valuable to o l required to reach the reproductive goals in d a i r y herds set by De K r u i f (1978): 1. A pregnancy rate of 80% a f t e r the f i r s t insemination 2. An average of 1.3 inseminations per conception. 3. An average i n t e r v a l of 85 days between p a r t u r i t i o n and conception. - 15 - 3. MATERIAL AND METHODS The data used in t h i s study was c o l l e c t e d from one dai r y herd. Milk progesterone l e v e l s were used to detect hormonal e s t r u s . The cows also were observed for behavioural estrus signs. At c a l v i n g each cow was ran- domly assigned to an e a r l y breeding or to a l a t e breeding group in order to achieve an unbiased t e s t of f e r t i l i t y in r e l a t i o n to days from p a r t u r i t i o n to conception (Whitmore et a l . , 1 974). Health codes were introduced to d i s t i n g u i s h between cows with normal and abnormal c a l v i n g and e a r l y post partum h i s t o r i e s of health problems. A f u r t h e r d i s t i n c t i o n was made between c a l v i n g in the pasture versus c a l v i n g in the non-pasture season. The data were subjected to an a n a l y s i s of variance to estimate d i f f e r e n c e s due to breeding time post partum, health status and c a l v i n g season. A general l i n e a r model was employed to t e s t reproduction t r a i t s of the current l a c t a t i o n , production t r a i t s and body weight changes of the current and subsequent l a c t a t i o n . Sources of un- c o n t r o l l e d v a r i a t i o n such as age, milk production in the f i r s t 50 days post partum and body weight changes in the f i r s t 60 days post partum were introduced as c o v a r i a b l e s into the s t a t i s t i c a l model. - 16 - 3.1. Animals From October 1977 through May 1979 125 post p a r t u r i e n t H o i s t e i n - F r i e s i a n cows of the d a i r y herd of the A g r i c u l t u r e Canada Research S t a t i o n in Agassiz, B.C. were sampled f o r milk progesterone analyses. The sampling s t a r t e d 6 days a f t e r c a l v i n g and was done every other day u n t i l conception occurred or the animal was removed from the herd. The time of t h i s t r i a l coincided with a d r a s t i c herd cutback so that only 85 cows had complete data. Another 14 cows were eliminated from the analyses of the subsequent l a c t a t i o n . The reasons f o r the c u l l i n g of the cows are l i s t e d in Table 1. Table 1: Reasons f o r c u l l i n g of the cows from the herd during the experiment. Reason Culled before Culled a f t e r conception conception Herd cutback, poor production old age 15 5 M a s t i t i s , udder problems 9 4 Displaced abomasum, i n j u r y , hardware 8 1 Hard breeders, s t e r i l e 8 Back in heat a f t e r confirmed c o n c e p t i o n , a b o r t i o n 4 Total 40 14 - 17 - The Agassiz dai r y herd was housed in a free s t a l l barn and the cows were milked in a double sawtooth p a r l o r . Part of the grain r a t i o n was fed during m i l k i n g in the p a r l o r . From May to October the cows were pastured on orchard grass pasture with approximately 10% white c l o v e r . A s t r i p grazing system was employed (the fence was moved every day so that the cows got a piece of fresh pasture each day). In wintertime (November t i l l A p r i l ) mainly corn s i l a g e with 2 kg of hay per cow per day was fed. ,A11 the cows were a r t i f i c i a l l y inseminated. Possible influences of the s e r v i c e s i r e on reproductive t r a i t s of the cow have not been taken i n t o account in t h i s study. Si r e s were randomly assigned to mates i r r e s p e c t i v e of treatment (e.g. e a r l y or l a t e breeding post partum) imposed on the cow. The conceptions were confirmed by r e c t a l palpation 2 months a f t e r insemination. 3.2. Milk sampling and milk progesterone analyses Samples of the milk s t r i p p i n g s were taken every other day at the afternoon m i l k i n g from 6 days post partum u n t i l conception occurred or the animal was removed from the herd. The analyses f o r milk progesterone were done employing the method described by Shelford et a l . (1979) which i s a m o d i f i c a t i o n of the radioimmunoassay technique f i r s t described by Heap et a l . (1973). - 18 - 3.3. Visual heat detection The cows were observed at m i l k i n g , at feeding time and one a d d i t i o n a l observation of the herd took place between 9:00 and 10:00 pm. Standing heat, increased a c t i v i t y and vaginal discharge was observed. No cameras, markers or other heat detection aids were used. During the time of t h i s study, a few cows which did not show any v i s i b l e signs of estrus were observed very c a r e f u l l y on the basis of the progesterone a n a l y s i s and inseminated when the progesterone l e v e l s i n d i c a t e d the cows' e s t r u s . 3.4. Data c o l l e c t i o n Information about the i n d i v i d u a l cows (age, repro- du c t i o n , health) was taken from the record keeping system of the A g r i c u l t u r e Canada Research S t a t i o n in Agassiz, B.C. Milk y i e l d was recorded at each m i l k i n g and percent f a t was evaluated at approximately 35 day i n t e r v a l s by an o f f i c i a l Record of Performance (R0P) milk t e s t e r . A l l the cows were weighed at c a l v i n g , 60 days and 80 days post par turn. - 19 - 3.5. Experimental design and s t a t i s t i c a l a n a l y s i s 3.5.1. L a c t a t i o n curve computation The computation of the l a c t a t i o n curves was done on the basis of milk y i e l d recordings taken every Wednesday throughout the year. A weekday was chosen to exclude a possible i n f l u e n c e of weekend milkers and weekend feeders. The 4% f a t corrected milk (FCM) was c a l c u l a t e d with the f o l l o w i n g formula: FCM (kg) = Milk (kg) x (.4 + .15 x f a t % ) . This formula was f i r s t proposed by Gaines (1928). Slopes and i n t e r c e p t s were c a l c u l a t e d f o r each cow using the "Eq u a l i t y of Regression Slopes Test" option of the covariance a n a l y s i s which i s part of the package program: Analysis of variance/covariance (UBC MFAV/1978). Slopes and i n t e r c e p t s were c a l c u l a t e d f o r m i l k , FCM production and fat-percent f o r the fol1owing 1actation i n t e r v a l s : Current l a c t a t i o n : 0 to 50 days 0 to 150 days 0 to 305 days 50 to 100 days 100 to 150 days 150 to 305 days Subsequent l a c t a t i o n : 0 to 50 days 0 to 150 days 50 to 100 days 100 to 150 days These slopes and i n t e r c e p t s were introduced i n t o the a n a l y s i s of variance as dependent v a r i a b l e s . - 20 - 3.5.2. Analyses of variance (ANOVA) model The data were subjected to an a n a l y s i s of variance. The f o l l o w i n g independent v a r i a b l e s were introduced: Groups: At c a l v i n g time each cow was randomly assigned to one of two groups. The e a r l y bred group was inseminated at the f i r s t v i s i b l e heat f o l l o w i n g 50 days post partum. The l a t e bred group was inseminated at the f i r s t v i s i b l e heat f o l l o w i n g 80 days post partum. Health s t a t u s : A health code was introduced to d i f - f e r e n t i a t e between cows with normal and abnormal c a l v i n g and e a r l y post partum h i s t o r i e s . Health code 1 represented a cow without c a l v i n g associated reproductive problems. Health code 2 represented a cow which had suffered one or more of the f o l l o w i n g c onditions at c a l v i n g or w i t h i n one month a f t e r c a l v i n g : c a l v i n g d i f f i c u l t y (more than two men or v e t e r i n a r y a s s i s t a n c e ) , retained placenta or m e t r i t i s . Ayalon et a l . (1971) used s i m i l a r health code s p e c i f i c a t i o n s . Calving season: Since there i s evidence in the l i t e r a t u r e that the c a l v i n g season has an inf l u e n c e on f e r t i l i t y and production in dai r y c a t t l e (De K r u i f , 1975; Francos and Rattner, 1975; Roine and' Saloniemi, 1978), season was introduced i n t o the general ANOVA model. The year was divided i n t o two seasons: May to October (pasture season) and November to A p r i l (non-pasture season). - 21 - The number of observations f o r the three independent v a r i a b l e s are l i s t e d in Table 2. Table 2: Number of observations Early bred group n Health code 1 Health code 2 Cows calved i n : Pasture season Non-pasture season 30 12 20 22 Late bred group n 30 1 3 18 25 Total n 60 251 38] 47J 85 85 Sources of uncontrolled v a r i a t i o n : Milk production of the f i r s t 50 days in the l a c t a t i o n was introduced in the general model as cov a r i a b l e to account f o r the d i f f e r e n c e s in milk production between the two groups. A pre l i m i n a r y a n a l y s i s of the data showed that the l a t e bred group produced more milk in t h i s period. The body weight change from c a l v i n g to 60 days post partum was introduced as cov a r i a b l e into the model f o r the same reason: Cows in the l a t e bred group l o s t more weight in t h i s period. These d i f f e r e n c e s between the two groups approached s i g n i f i c a n c e and i n d i c a t e d that the two groups were not randomly assigned in r e l a t i o n to these two t r a i t s . Age at c a l v i n g was introduced as c o v a r i a b l e to account for the i n f l u e n c e of the age of the cow on i t s f e r t i l i t y and producti on. - 22 - The f o l l o w i n g dependent v a r i a b l e s were tested in the analyses of variance: Reproductive t r a i t s : Occurrence of f i r s t v i s i b l e and f i r s t progesterone detected heats (days post partum), f i r s t estrous cycle length (days), days from p a r t u r i t i o n to the f i r s t s e r v i c e , number of s e r v i c e s per conception, days open, days from f i r s t s e r v i c e to conception and the c a l v i n g i n t e r v a l (days). Productive t r a i t s : Slopes of l a c t a t i o n curves (as d i s - cussed under 3.5.1.). Milk production, FCM production and fat-percent of the f o l l o w i n g l a c t a t i o n i n t e r v a l s : In a d d i t i o n the average d a i l y milk production from the beginning of the current l a c t a t i o n to day 150 of the subsequent l a c t a t i o n was t e s t e d . Body weights and body weight changes: Calving weights, weight of c a l v e s , body weight changes from p a r t u r i t i o n to 60 days and 80 days post partum in both the current and the subsequent l a c t a t i o n , the body weight gain between c a l v i n g s and the rate of gain (kg/day) from 60 and 80 days post partum to the subsequent c a l v i n g . Current l a c t a t i o n 0 0 50 100 to 50 days to 305 days to 100 days to 150 days Subsequent l a c t a t i o n : 0 50 100 to 50 days to 100 days to 150 days - 23 - The f o l l o w i n g general l i n e a r model was employed: Y i j k l - /+> + A i + B j + C k + A B i j + B C j k + A B C i j k + dD . •, n + f F . •, , + fG. .. , + 6 . . , , l j k l i j k l i j k l i j k l where: Y^.^ = dependent v a r i a b l e (the observation of the 1-th cow) as l i s t e d above jAU = o v e r a l l mean A. = the e f f e c t of the i - t h breeding group B. = the e f f e c t of the j - t h health code 3 C ̂  = the e f f e c t of the k-th c a l v i n g season D,• ikI = the co v a r i a b l e milk production 0-50 days of J the 1-th cow in the i - t h group with the j - t h health code and c a l v i n g i n the k-th season d = the c o e f f i c i e n t associated with the D... cov a r i a b l e 1 J F. .J, = the c o v a r i a b l e body weight changes 0-60 J days post partum of the 1-th cow i n the i - t h group with the j - t h health code and c a l v i n g in the k-th season f = c o e f f i c i e n t associated with the F... cov a r i a b l e 1 J G. .., = the co v a r i a b l e age (mo.) of the 1-th cow 1 J in the i - t h group with the j - t h health code and c a l v i n g in the k-th season g = the c o e f f i c i e n t associated with the G... cov a r i a b l e 1 J 6...-, = the unexplained d e v i a t i o n s associated with ' J the 1-th cow. Assumed to be random with a mean of zero and variance ofCT|. - 24 - For the c a l c u l a t i o n of the a n a l y s i s of variance the package program UBC BMD10V (General Linear Hypothesis) was employed. The t e s t s for s i g n i f i c a n c e were generated with the F-test on a basis of e r r o r p r o b a b i l i t i e s of P-6 .05 and P^.01. In order to explain s i g n i f i c a n t i n t e r a c t i o n s , analyses were computed w i t h i n health codes or w i t h i n seasons using the same general model excluding the appropriate main e f f e c t s and i n t e r a c t i o n s . 3.5.3. Tests of influ e n c e of days open on production in subsequent l a c t a t i o n Days open were c h a r a c t e r i z e d by a large v a r i a t i o n and were shown by Ripley et a l . (1970) to in f l u e n c e the pro- duction in the subsequent l a c t a t i o n . Single regression analyses with days open as a continuous independent v a r i a b l e were computed to t e s t the influ e n c e of days open on pro- duction t r a i t s in the subsequent l a c t a t i o n . For the regres- sion analyses the package program UBC TRP (Tri a n g u l a r Regression Package, 1977) was used. 3.5.4. C o r r e l a t i o n c o e f f i c i e n t s The c o r r e l a t i o n c o e f f i c i e n t s discussed l a t e r are simple product moments among a l l continuous v a r i a b l e s . For the c a l c u l a t i o n of the c o r r e l a t i o n c o e f f i c i e n t s the package program UBC TRP (Tri a n g u l a r Regression Package, 1977) was used. - 2 5 - 4. RESULTS 4.1. Test f o r bias in the groups The t e s t for bias showed that there were no s i g n i f i c a n t d i f f e r e n c e s between the two groups at the time of c a l v i n g and in the e a r l y post partum period in terms of productive and reproductive t r a i t s (Table 3). However, the milk production in the f i r s t 50 days of the l a c t a t i o n and the body weight changes (BWC) from c a l v i n g to 60 days post partum approached s i g n i f i c a n c e , t h e r e f o r e , these v a r i a b l e s were introduced as c o v a r i a b l e s in the main model of the a n a l y s i s of variance. - 26 - Table 3: Means and standard d e v i a t i o n s of t r a i t s at the time of c a l v i n g and in the e a r l y post partum period. E a r l y bred Late bred T r a i t group group x * s.d. x * s.d. Age of cows (mos.) 44.90 20.00 46.20 22.70 Lac t a t i o n number 2.45 1 .35 2. 56 1 .67 Calving wt. (kg) 618 98 611 97 Wt. of c a l f (kg) 42.50 5. 30 43.20 5 .70 BWC 0-60 days p.p. (kg) -40.80 37.10 -54.40 40. 90 Milk 0-50 days (kg) 1520 325 1653 380 Fat % 0-50 days 3.48 .53 3. 38 .52 FCM 0-50 days (kg) 1401 31 0 1 509 416 Slope of milk 0-50 days .1 509 .1253 .1779 . 1 349 Slope of f a t % 0-50 days - .0035 .0061 .0030 .0076 Slope of FCM 0-50 days .1257 .1138 .1535 .1387 •Number of observations: 42 f o r the e a r l y bred group , 43 in the l a t e bred group except f o r the weight of the c a l f (33 and 36 r e s p e c t i v e l y ) . There were no s i g n i f i c a n t (P<£.05) d i f f e r e n c e s between the e a r l y bred and the l a t e bred group i n the t r a i t s l i s t e d above. - 27 - 4.2. Reproductive t r a i t s The d e t a i l e d tables for reproductive t r a i t s of the current l a c t a t i o n are shown in the Appendix (Tables 2a and 2b) . The f i r s t cycle length was defined as time period from the f i r s t r i s e of the milk progesterone concentration from 2ng/ml (the e a r l y post partum concentration) to a concentration above 5ng/ml and back to 2ng/ml (Figure 1). The duration of a normal estrous cycle of a cow i s 19 to 23 days. The average f i r s t cycle length i n t h i s experiment was found to be only 17.4 ± 7.5 days, with a wide range from 8 days to 40 days. The f i r s t progesterone detected heat was defined as the f i r s t drop of the milk progesterone concentration below 2ng/ml a f t e r the concentration had been above 5ng/ml for the f i r s t time a f t e r p a r t u r i t i o n (Figure 1). The f i r s t progesterone detected heat •> occurred 33 ± 10 days post partum with a range of 19 to 78 days. The f i r s t v i s i b l e heat occurred 49 ± 26 days post partum with a range of 8 to 127 days. - 28 - Figure 1: D e f i n i t i o n s of the f i r s t estrous cycle length and the f i r s t progesterone detected heat on the base of milk progesterone l e v e l s i n the e a r l y post partum period. days post partum A : f i r s t r i s e of the milk progesterone concentration post partum above 2ng/ml B : f i r s t progesterone detected heat AB: duration of the f i r s t estrous cycle BC: duration of the second estrous c y c l e - 29 - 4.2.1. Influence of e a r l y versus l a t e breeding There was no d i f f e r e n c e between the e a r l y bred group and the l a t e bred group in terms of the occurrence of the f i r s t v i s u a l l y : o r progesterone detected heats and the length of the f i r s t estrous cycle (Table 4). The l a t e bred group had more recorded v i s i b l e heats and progesterone detected heats than the e a r l y bred group due to a longer period from p a r t u r i t i o n to the f i r s t s e r v i c e which was imposed on the cows by the treatment (e a r l y and l a t e breeding). On the average the e a r l y bred group was inseminated 72 ±18 days a f t e r p a r t u r i t i o n and the l a t e bred group was inseminated 93 ± 17 days a f t e r p a r t u r i t i o n . The e a r l y bred group had 88 ± 33 days open while the l a t e bred group had 120 ± 40 days open which r e s u l t e d i n c a l v i n g i n t e r v a l s of 373 ± 34 versus 404 + 38 days r e s p e c t i v e l y . The e a r l y bred group needed s i g n i f i c a n t l y fewer serv i c e s per conception (1.50; range 1 to 3) than the l a t e bred group (1.95; range 1 to 5). Therefore, the e a r l y bred group also had fewer days from the f i r s t s e r v i c e to conception (16.4 versus 26.2). None of the covariables accounted f o r a s i g n i f i c a n t amount of the v a r i a t i o n in reproductive t r a i t s (means and standard deviations of c o v a r i a b l e s , Appendix Table 1). S i g n i f i c a n t i n t e r a c t i o n s w i l l be discussed below. - 30 - Table 4: Means and standard dev i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between the e a r l y bred and the l a t e bred group. Early bred Late bred Sign T r a i t group group X s.d. X s.d 1st v i s i b l e heat (d.p.p.) 50 28.5 47 25 . 2 n.s. 1st prog. det. heat (d.p.p.) 34 10.0 33 10. 5 n.s. Number of v i s i b l e heats 2.2 1 .0 3.0 1 . 7 ** Number of prog. det. heats 3.1 1 .4 4.2 1 . 3 ** 1st cycle length (days) 18.4 8.6 16.6 6. 2 n.s. Days to 1st. s e r v i c e 72 18.2 93 1 7 . 3 ** Number of ser v i c e s 1 .50 1 .95 * Days from 1st se r v i c e to conception 1 6.40 25.0 26 . 2 39. 8 ** Days open 88 33.0 121 40. 6 ** Calving i n t e r v a l (days) 373 34.1 404 38. 0 ** S i g n i f i c a n t d i f f e r e n c e s between groups: * P ^ . 0 5 , * * P s ? . 0 1 , n.s. = not s i g n i f i c a n t . - 31 - 4.2.2. Inf1uence of health The onset of the estrous cycle and the days from p a r t u r i t i o n to the f i r s t s e r v i c e were not influenced by the health status (Table 5). The duration of the f i r s t c ycle was s l i g h t l y shorter in cows with health problems, t h i s d i f f e r e n c e , however, was n o t . s i g n i f i c a n t . Cows with health problems needed more servic e s per conception (1.96 versus 1.63), had more days open (113 versus 100) and had a longer c a l v i n g i n t e r v a l (400 versus 385 days) than the cows without c a l v i n g or e a r l y post partum reproductive problems i r r e s p e c t i v e of date of breeding. S i g n i f i c a n t i n t e r a c t i o n s w i l l be discussed below. - 32 - Table 5: Means and standard d e v i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between the two health codes. Health code Health code T r a i t X S . 1 d . X s.d. 1st v i s i b l e heat (d.p.p.) 49 27 .6 47 25.0 n.s. 1st prog. det. heat (d.p.p.) 34 11 .1 34 8.2 n.s. Number of v i s i b l e heats 2.5 1 .2 2.8 2.0 n.s. Number of prog. det. heats 3.7 1 .4 3.7 1 .6 n.s. 1st cycle length (days) 18.1 8 .3 15.9 4.7 n.s. Days to 1st. s e r v i c e 82 21 .5 83 18.9 n.s. Number of servic e s 1 .63 1 .96 * Days from 1st s e r v i c e to conception 18.7 2 9 .9 27.9 40.9 ** Days open 1 00 38 113 46 ** Calving i n t e r v a l (days) 385 35 400 47 ** S i g n i f i c a n t d i f f e r e n c e s between health codes: * P=s ** P ^ .01, n.s. = not s i g n i f i c a n t . The number of observations were 60 f o r health code 1 and 25 f o r health code 2, except f o r the c a l v i n g i n t e r v a l (49 and 22 observations r e s p e c t i v e l y ) . - 33 - 4.2.3. Influence of c a l v i n g season Pasture season versus non-pasture season influenced the reproductive performance very l i t t l e . There were no s i g n i f i c a n t d i f f e r e n c e s in the onset of the estrous c y c l e , detected heats, days from p a r t u r i t i o n to the f i r s t s e r v i c e and the number of s e r v i c e s needed per conception (Table 6). The d i f f e r e n c e s between the c a l v i n g season f o r days from the f i r s t s e r v i c e to conception, days open and the c a l v i n g i n t e r v a l reached s i g n i f i c a n c e with r e l a t i v e l y small d i f f e r e n c e s . These d i f f e r e n c e s have to be explained in r e l a t i o n to some s i g n i f i c a n t i n t e r a c t i o n s between group and c a l v i n g season or health status and c a l v i n g season. The i n t e r a c t i o n s w i l l be discussed below. 4.2.4. I n t e r a c t i ons S i g n i f i c a n t i n t e r a c t i o n s in reproductive t r a i t s are l i s t e d in Table 7. In order to explain the s i g n i f i c a n t i n t e r a c t i o n s , the r e s u l t s of an a n a l y s i s w i t h i n group, health code and/or c a l v i n g season were used. Within the e a r l y bred group health status and c a l v i n g season did not i n f l u e n c e the number of ser v i c e s per conception. Within the l a t e bred group, however, cows with health code 2 (problem cows) needed s i g n i f i c a n t l y more servic e s per conception (2.46; range 1 to 5) versus the healthy cows (1.73; range 1 to 4). A s i m i l a r explanation can be - 34 - Table 6: Means and standard d e v i a t i o n s of reproductive t r a i t s and t h e i r d i f f e r e n c e s between pasture season and non-pasture season. Pasture Non-Pasture T r a i t season season Sign X s.d. X s . d. 1st v i s i b l e heat (d.p.p.) 49 : 28.3 48 25 .8 n. s. 1st prog. det. heat (d.p.p.) 32 8.6 35 11 .4 n . s . Number of v i s i b l e heats 2 . 5 1.1 2.7 1 .7 n. s. Number of prog. det. heats 3.7 1 .3 3.7 1 .6 n . s . 1st cycle length (days) 17.4 4.5 17.6 9 .2 n. s . Days to 1st se r v i c e 83 22.8 82 18 .9 n. s . Number of se r v i c e s 1 .74 1 .72 n. s . Days from 1st ser v i c e to conception 23.0 36 . 5 20.1 31 . 2 * Days open 1 06 42 1 03 39 * Calving i n t e r v a l (days) 39 T 40 387 39 * S i g n i f i c a n t d i f f e r e n c e s between pasture and non-pasture season:;: * P^s.05, n.s. = not s i g n i f i c a n t The number of observations were 38 for the pasture season and 49 f o r the non-pasture season. - 35 - given f o r the group-season i n t e r a c t i o n : Within the e a r l y bred group, c a l v i n g season had no i n f l u e n c e on the number of s e r v i c e s per conception (1.53 versus 1.42) while w i t h i n the l a t e bred group, the cows that calved during the pasture season needed s i g n i f i c a n t l y more i n - seminations per conception than cows c a l v i n g in the non- pasture season (2.1 versus 1.8). Within the e a r l y bred group, days open, days from the f i r s t s e r v i c e to conception and the c a l v i n g i n t e r v a l were not s i g n i f i c a n t l y i n fluenced by health status or c a l v i n g season. However, w i t h i n the l a t e bred group, days open and the c a l v i n g i n t e r v a l were s i g n i f i c a n t l y influenced by health s t a t u s ; days open and days from the f i r s t s e r v i c e to conception were influenced by the c a l v i n g season (Tables 8 to 11). The health status season i n t e r a c t i o n f o r the c a l v i n g i n t e r v a l was s i g n i f - i c a n t in the general model and w i t h i n the e a r l y bred group, but not w i t h i n the l a t e bred group. Health had a s i g n i f i c a n t inf1uence on the c a l v i n g i n t e r v a l during the pasture season but not during the non-pasture season (Table 12). The general model showed a s i g n i f i c a n t three- way i n t e r a c t i o n (group-health-season) for days from f i r s t s e r v i c e to conception. This i n t e r a c t i o n can be neglected because in the pasture season in the l a t e bred group, there was only one animal with health code 2 and t h i s animal had an extreme value (136 days). •r 36 - Table 7: I n t e r a c t i o n s between groups, health codes and seasons i n reproductive t r a i t s . Tra i ts Interact!' on Group x Health code I n t e r a c t i on Group x Season I n t e r a c t i o n Health x Season Number of se r v i c e s per conception Days open Days from 1st se r v i c e to conception Calving i n t e r v a l ** n.s, ** ** n . s ;n. s, : n. s n. s P ̂  .05, * P •== .01 , n.s not s i g n i f i c a n t Table 8: S i g n i f i c a n t group-health code i n t e r a c t i o n s i n reproductive t r a i t s . A n a l y s i s w i t h i n the e a r l y bred group. Early bred group Tra i t Health code 1 Health code 2 x n s.d. X n s .d. Sign Number of ser v i c e s per conception 1 .53 30 . 68 1 .42 12 .79 n.s. Days open 89 30 35 87 12 27 n.s. Calving i n t e r v a l 374 23 37 370 10 26 n.s. n.s. = not s i g n i f i c a n t - 37 - Table 9: S i g n i f i c a n t groups-health code I n t e r a c t i o n s i n reproductive t r a i t s . A n a l y s i s w i t h i n the l a t e bred group. Late bred group T r a i t Health code 1 Health code 2 X n s. d. X n s.d. Sign Number of ser v i c e s per conception 1 .73 30 1 . 48 2.46 1 3 2.46 * Days open 11 3 30 36 1 39 1 2 47 ** Calving i n t e r v a l 394 26 29 426 1 2 46 * * S i g n i f i c a n t d i f f e r e n c e s : * P ^ .05, ** P ^ .01 Table 10: S i g n i f i c a n t group-season i n t e r a c t i o n s i n reproductive t r a i t s . A n a l y s i s w i t h i n the e a r l y bred group. T r a i t Early bred group Pasture season Non-Pasture season Number of s e r v i c e s per conception Days open Days from 1st s e r v i c e to concep. X n s.d. X n s.d. Sign. 1 .45 20 .60 1 .55 22 .80 n.s. 89 20 35 87 22 32 n.s. 15.1 20 22.0 17.6 22 28.0 n.s. n.s. = not s i g n i f i c a n t - 38 - t r a i t s . A n a l y s i s w i t h i n t h e 1 a t e b r e d g r o u p . L a t e b r e d g r o u p T r a i t P a s t u r e . : s e a s o n N o n - P a s t u r e s e a s o n X n s . d . X n s . d . S i g n N u m b e r o f s e r v i c e s p e r c o n c e p t i o n 2 . 0 6 18 1 . 7 3 1 . 8 8 25 1 . 4 5 n . s . D a y s o p e n 125 18 44 118 24 38 * D a y s f r o m 1 s t s e r v i c e t o c o n c e p . 31 . 8 18 47 22 25 34 ** S i g n i f i c a n t d i f f e r e n c e s : * P ^ . 0 5 , * * P ^ . 0 1 n . s . = n o t s i g n i f i c a n t T a b l e 1 2 : S i g n i f i c a n t s e a s o n - h e a l t h c o d e i n t e r a c t i o n f o r t h e c a l v i n g i n t e r v a l . A n a l y s i s w i t h i n s e a s o n s H e a l t h c o d e 1 H e a l t h c o d e 2 T r a i t X n s . d . X n s . d . S i g n P a s t u r e s e a s o n 3 8 2 27 37 41 2 5 52 * N o n - p a s t u r e s e a s o n 387 22 32 397 17 47 n . s . T o t a l 3 8 5 49 35 4 0 0 22 47 * * S i g n i f i c a n t d i f f e r e n c e s : * P is. . 0 5 , n . s . = n o t s i g n i f i c a n t * * P ^ . 0 1 - 39 - 4.3. Body weights and body weight changes i n the current 1 a c t a t i on The d e t a i l e d tables f o r body weights and body weight changes are presented in the Appendix (Tables 4a and 4b). 4.3.1. Influence of e a r l y versus l a t e breeding The e a r l y post partum body weight changes were not influenced by the d i v i s i o n of the herd i n t o e a r l y bred and l a t e bred groups (Table 13). Body weight changes were s i g n i f i c a n t l y c o r r e l a t e d to production (Appendix Table 8). The weight of the cows at the subsequent c a l v i n g was s i g n i f i c a n t l y higher f o r cows i n the l a t e bred group (689 kg) as compared to cows in the e a r l y bred group (657 kg). The body weight gain from c a l v i n g to c a l v i n g was a l s o s i g n i f i c a n t l y higher i n the l a t e bred group (67 kg versus 45 kg). The average d a i l y weight gain from 60 and 80 days post partum r e s p e c t i v e l y to the subsequent c a l v i n g was also higher i n the l a t e bred group. The higher average rate of gain in the l a t e bred group can be explained with the longer dry period of these cows. The weight gain during l a c t a t i o n was highly c o r r e l a t e d with age , (r = -.66), and the c o v a r i a b l e age accounted for a s i g n i f i c a n t amount of the v a r i a t i o n . - 40 - T a b l e 1 3 : Means and s t a n d a r d d e v i a t i o n s o f body w e i g h t s and body w e i g h t c h a n g e s (BWC) i n t h e c u r r e n t l a c t a t i o n and a t t h e s u b s e q u e n t c a l v i n g . The d i f f e r e n c e s b e t w e e n e a r l y b r e d and l a t e b r e d g r o u p . E a r l y , b r e d g r o u p L a t e b r e d g r o u p T r a i t ( k g ) X n s . d . X n s . d . S i g n Wt . a t c a l v i n g - ( l ) 611 42 97 .0 625 43 1 0 0 . 7 n . s . BWC 0 - 6 0 d . p . p . -41 42 3 7 . 1 - 5 4 43 4 0 . 9 n . s . BWC 0 - 8 0 d . p . p . -31 42 4 0 . 1 - 5 0 42 41 .6 n . s . BWC 6 0 - 8 0 d . p . p . 1 0 40 2 3 . 0 6 40 2 2 . 5 n . s . BWC/day ( k g / d a y ) : 60 d . p . p . t o c a 1 v i n g - ( 2 ) . 28 33 . 1 6 ' . 3 5 38 . 1 4 * 80 d . p . p . t o c a l v i n g - ( 2 ) . 2 7 33 . 17 . 3 5 38 . 1 6 * Wt. a t c a l v i n g - ( 2 ) 657 31 6 0 . 9 689 38 5 9 . 0 * BWC c a l v i n g - ( 1 ) t o c a l v i n g - ( 2 ) 45 31 66 . 5 67 37 7 0 . 2 ** Wt. o f c a l f ( 1 ) 4 2 . 0 33 4 . 9 4 3 . 2 36 5 . 8 n . s . Wt . o f c a l f ( 2 ) 4 7 . 2 32 7 . 7 4 5 . 4 36 6 . 5 n . s . S i g n i f i c a n t d i f f e r e n c e s : * s i g n i f i c a n t . P =s . 0 5 , * * P = .01 , n . s . = n o t ( 1 ) = c u r r e n t c a l v i n g . ( 2 ) = s u b s e q u e n t c a l v i n g d . p . p . = d a y s p o s t p a r t u m - 41 - 4.3.2. Influence of health Cows with c a l v i n g d i f f i c u l t i e s or e a r l y post partum reproductive problems had heavier calves than cows without problems (Table 16). The 25 cows with problems had 16 b u l l calves and 9 h e i f e r calves (Table 14). B u l l calves tend to be heavier than h e i f e r calves and are more l i k e l y to cause d i f f i c u l t i e s at c a l v i n g than h e i f e r calves ( P h i l i p s s o n , 1976). The weight of the c a l f at the sub- sequent c a l v i n g again was heavier f o r the cows with health code 2 and again they had more b u l l calves than h e i f e r calves (14 b u l l s , 8 h e i f e r s ) . The body weight at the subsequent c a l v i n g was the same f o r both health code groups. Cows with health code 2 gained more weight during the current l a c t a t i o n , the rate of gain (60 days and 80 days post partum r e s p e c t i v e l y to the subsequent c a l v i n g ) however was s i g n i f i c a n t l y d i f f e r e n t (Table 16). The group-health status i n t e r a c t i o n f o r body weight gain between ca l v i n g s was s i g n i f i c a n t (P ̂  .05). The an a l y s i s w i t h i n groups and health codes (Table 15) demons- t r a t e d that w i t h i n the e a r l y bred group the health code did not account f o r a s i g n i f i c a n t amount of the v a r i a t i o n while i t was s i g n i f i c a n t w i t h i n the l a t e bred group. Hence, cows with c a l v i n g or e a r l y post partum problems in the l a t e bred group gained much more weight than cows of the same group without problems or a l l the cows in the ea r l y bred group. - 42 - Table 14: Sex of calves Current b u l l s Early bred group 20 Late bred group 23 Health code 1 27 Health code 2 16 Pasture season 17 Non-Pasture season 26 c a l v i n g Subsequent c a l v i n g h e i f e r s b u l l s h e i f e r s 22 21 12 20 13 25 33 20 29 9 14 8 21 14 18 21 20 19 Table 15: Group health status i n t e r a c t i o n f o r body weight gain (kg) between c a l v i n g s . The a n a l y s i s w i t h i n breedirig groups. Health code 1 Health code 2 X n s.d • X n s.d. Sign. Early bred group 42 22 62 . 1 53 9 79.4 n.s. Late bred group 45 25 60. 3 111 1 2 70.5 * Total 44 47 60. 5 86 21 78.5 * S i g n i f i c a n t d i f f e r e n c e s : * P .05, n.s. = not s i g n i f i c a n t - 43 - Table 16: Means and standard deviations of body weights and body weight changes (BWC) i n the current l a c t a t i o n and at the subsequent c a l v i n g . The d i f f e r e n c e s between health codes. T r a i t s (kg) Health X code n 1 s.d. Health x code • 2 n s.d. Sign Wt. at calving-(1 ) 630 60 94.8 588 25 102.1 n.s. BWC 0-60 d.p.p. -51 59 38.3 -39 25 41 .4 n.s. BWC 0-80 d.p.p. -46 59 39.8 -25 24 43.3 n.s. BWC 60-80 d.p.p. 6 56 21 .0 14 24 26.1 n.s. BWC/day (kg/day): 60 d.p.p. to ca1vi ng-(2 ) . 30 49 .14 .35 22 .18 n.s. 80 d.p.p. to ca1vi ng-(2 ) . 30 49 .15 .33 22 .18 n.s. Wt. at c a l v i n g - ( 2 ) 674 48 60.8 674 21 64.9 n.s. BWC cal v i n g - ( l ) to c a l v i n g - ( 2 ) 44 47 60.5 86 21 78. 5 * Wt. of c a l f (1 ) 42.1 47 4.9 43.8 22 5.9 * Wt. of c a l f (2) 45.1 46 7.2 48. 5 22 6.6 * S i g n i f i c a n t d i f f e r e n c e s : * P ^ .05, n.s. = not s i g n i f i c a n t (1) = current c a l v i n g , (2) subsequent c a l v i n g d.p.p. = days post partum - 44 - 4.3.3. Influence of season The season had a marked in f l u e n c e on body weight and body weight changes (Table 17). The c a l v i n g weight of the cows c a l v i n g during the pasture season was s i g n i f i c a n t l y higher than the weight of the cows c a l v i n g in the non- pasture season. The cows c a l v i n g in the pasture season also l o s t more weight in the f i r s t 80 days of the l a c - t a t i o n . The d i f f e r e n c e between the two seasons was e s p e c i a l l y marked f o r the i n t e r v a l between 60 and 80 days post partum, where cows in the pasture season s t i l l were l o s i n g weight while cows i n the non-pasture season already s t a r t e d to gain weight again. The rate of gain showed the same s i t u a t i o n : Cows c a l v i n g during the pasture season had a s i g n i f i c a n t l y lower rate of gain from 60 days post partum to the subsequent c a l v i n g . The same c a l c u l a t i o n from 80 days post partum to the subsequent c a l v i n g revealed no s i g n i f i c a n t d i f f e r e n c e s between cows ca l v i n g during the pasture season versus cows c a l v i n g during the non-pasture season. Cows c a l v i n g in the non- pasture season in t o t a l gained more weight during the l a c t a t i o n up to the subsequent c a l v i n g . At the subsequent c a l v i n g , there were no d i f f e r e n c e s between the two seasons in terms of the body weight of the cow and the c a l f . - 45 - Table 17: Means and standard dev i a t i o n s of body weight and body weight changes (BWC) in the current l a c t a t i o n and at the subsequent c a l v i n g . The d i f f e r e n c e s between cal v i n g s during the pasture season and non-pasture season. T r a i t (kg) Pasture season Non-Pasture season X n s . d. X n s.d. Sign Wt. at c a l v i n g - ( l ) 648 38 90 . 7 595 47 98.9 * BWC 0-60 d.p.p. -53 38 31 .2 -43 47 45.1 n.s. BWC 0-80 d.p.p. -56 37 26 .8 -28 47 47 .1 * * BWC 60-80 d.p.p. - 2 35 21 . 3 1 6 45 20 . 7 ** Wt. at c a l v i n g - ( 2 ) 683 32 55 .8 667 37 66 . 2 n.s. BWC/day (kg/day): 60 d.p.p.-calving -(2) .25 33 • • 14 .37 38 . 1 5 * 80 d.p.p .-cal vi ng -(2) .26 33 • 16 .34 38 .17 n.s. BWC c a l v i n g - ( l ) to c a l v i n g - ( 2 ) 26 31 61 . 2 80 37 65.8 ** Wt. of c a l f (1) 44 31 5 .8 41 38 4.6 * Wt. of c a l f (2) 47 31 8 .3 46 37 6.0 n.s. S i g n i f i c a n t d i f f e r e n c e s : *P . 05, ** p £.01 , n.s. = not s i g n i f i c a n t . (1) current c a l v i n g , (2) subsequent c a l v i n g d.p.p. = days post partum - 46 - .4.4. Productive t r a i t s in. the current l a c t a t i o n The d e t a i l e d tables f o r productive t r a i t s of the current l a c t a t i o n are presented in the Appendix (Tables 3a and 3b). The co v a r i a b l e milk production 0-50 days post partum as expected, accounted for a s i g n i f i c a n t amount of the v a r i a t i o n in most production t r a i t s . 4.4.1. Influence of e a r l y versus l a t e breeding The cows i n the l a t e bred group produced more milk in the 305 day l a c t a t i o n and also more f a t corrected milk (FCM) (Table 18). The slopes for the period from 150 days to 305 days of the l a c t a t i o n f o r milk and FCM were also s i g n i f i c a n t l y d i f f e r e n t . Cows in the l a t e bred group had a greater persistency in the l a t t e r part of the l a c t a t i o n (Figure 2). - 47 - Table 18: Means and standard d e v i a t i o n s of productive t r a i t s in the current l a c t a t i o n and the d i f f e r e n c e s between e a r l y bred and l a t e bred group Ear l y bred Late bred T r a i t group x s.d. group x s.d. Sign. FCM 0-50 days (kg) 1401 31 0 1 509 416 n.s. FCM 50-100 days (kg) 1386 285 1412 612 n.s. FCM 100-150 days (kg) 1 284 233 1 31 3 303 n.s. FCM 305 days (kg) 7276 1 565 7995 2304 * Milk 305 days (kg) 7595 1659 8550 2484 * Fat % 305 days 3.71 .47 3. 57 .38 n.s. Slope milk 0-150 days -.0271 .0366 --.0372 .0639 n.s. Slope f a t % 0-150 days -.0013 .0034 -.0016 .0036 n.s. Slope FCM 0-150 days -.0290 .0420 -.0405 .0648 n.s. Slope milk 150-305 days -.1178 .0487 -.0955 .0448 ** Slope f a t % 150-305 days .0009 .0008 .0010 .0119 n.s. Slope FCM 150-305 days -.1059 .0430 -. 0825 .0419 * * S i g n i f i c a n t d i f f e r e n c e s between groups: * P ^ . 05, ** P ̂  .C n.s. = not s i g n i f i c a n t . - 48 - Figure 2: Mean production and slopes of e a r l y and l a t e bred group f o r f a t %, milk and f a t corrected milk (FCM) of the current l a c t a t i o n . Early bred group Late bred group days of current l a c t a t i o n - 49 - 4.4.2. Influence of health The grouping of the herd according to health codes did not i n f l u e n c e the productive performance of the cows. None of the analysed production t r a i t s of the current l a c t a t i o n showed a s i g n i f i c a n t d i f f e r e n c e between the two health code groups. Figure 3 shows that there were small d i f f e r e n c e s in the f a t % i n the milk; cows with e a r l y post partum reproductive disorders produced less f a t than the heal thy. cows.(Fi gure 3). In terms of milk or FCM production, there were no s i g n i f i c a n t d i f f e r e n c e s in the f i r s t part of the l a c t a t i o n . Milk or FCM production in the l a t t e r part of the l a c t a t i o n was e x a c t l y the same f o r both of the health code groups (Figure 3). 4.4.3. Influence of season The i n f l u e n c e of the c a l v i n g season on production in the current l a c t a t i o n was not s u b s t a n t i a l (Figure 4). Cows c a l v i n g in the pasture season had a s i g n i f i c a n t l y (P6.05) higher f a t t e s t up to 150 days in the l a c t a t i o n (3.51% ± .48% versus 3.25% ± .36%) and produced s i g n i - f i c a n t l y (P*.05) more FCM in the t o t a l l a c t a t i o n (7880 kg ± 2011 kg versus 7507 kg ± 1992 kg). The uncorrected milk y i e l d was not s i g n i f i c a n t l y d i f f e r e n t . The slopes of f a t %, milk and FCM production did not show any s i g n i f i c a n t d i f f e r e n c e s between the two c a l v i n g seasons (Figure 4). - 5 0 - 3: Mean production and slopes of health code group 1 and health code group 2 f o r f a t %, milk and f a t corrected milk (FCM) of the current l a c t a t i o n . Health code group 1 Health code group 2 days of current l a c t a t i o n - 51 - Figure 4: Mean production and slopes of cows c a l v i n g during the pasture season versus the non- pasture season for f a t %, milk and f a t corrected milk (FCM) of the current l a c t a t i o n . —• Pasture season — Non-Pasture season 0 50 100 150 200 250 305 days of current l a c t a t i o n - 52 - 4.5. Carry-over e f f e c t s from the current to the sub- sequent l a c t a t i o n The d e t a i l e d tables f o r t r a i t s in the subsequent l a c t a t i o n are presented in the Appendix (Tables 5a and 5b). 4.5.1. Influence of e a r l y versus l a t e breeding The body weight changes i n the e a r l y post partum period of the subsequent l a c t a t i o n were not s i g n i f i c a n t l y d i f f e r e n t between the two groups (Table 19). There were some s i g n i f i c a n t d i f f e r e n c e s in terms of milk production: Cows in the l a t e bred group produced s i g n i f i c a n t l y more f a t corrected milk (FCM) in the periods 50 to 100 and 100 to 150 days post partum. Mean production and slopes of f a t %, milk and FCM of the subsequent l a c t a t i o n are presented in Figure 5. The common slopes f o r milk and FCM f o r the period 0-150 days of the two groups were s i g n i f i c a n t l y d i f f e r e n t . However, the slopes of the d i f f e r e n t segments of the l a c t a t i o n did not show any s i g n i f i c a n t d i f f e r e n c e s (Figure 5). - 53 - Table 19: Means and standard de v i a t i o n s of t r a i t s in the subsequent l a c t a t i o n and the d i f f e r e n c e s between e a r l y and l a t e bred groups. Early bred Late bred T r a i t group X s.d. group x s.d. Si BWC 0-60 d.p.p. (kg) -55 33.0 -66 39.4 n. BWC 0-80 d.p.p. (kg) -32 45.9 -54 43.9 n . BWC 60-80 d.p.p. (kg) 18 22.5 8 27 .9 n. FCM 0-50 days p.p. (kg) 1 540 40.6 1745 253 n . FCM 50-100 days p.p. (kg) 1 554 160 1689 21 2 * FCM 1 00-1 50 days p .p.(kg) 1351 161 1479 188 * Slope milk 0-150 d.p.p. 0640 .0353 -.0318 .0361 ** Slope f a t % 0-150 d.p.p. -. 0025 . 0055 -.0036 .0054 n. Slope FCM 0-150 d.p.p. 0709 .0302 -.0492 .0390 * S i g n i f i c a n t d i f f e r e n c e s : * s i g n i f i c a n t 05, ** P SE- . 01 , n . s. = not Number of observations were 27 f o r the l a t e bred group. 25 f o r the e a r l y bred group and BWC = body weight changes, d.p.p . = days post partum - 54 - Figure 5: Mean production and slopes of e a r l y and l a t e bred group f o r f a t %, milk and f a t corrected milk (FCM) of the subsequent l a c t a t i o n (0- 150 days ) . Early bred group Late bred group I 1 1 1—„ 0 50 100 150 days of subsequent l a c t a t i o n - 55 - 4.5.2. Influence of health Among the production t r a i t s , the only s i g n i f i c a n t d i f f e r e n c e between the two health code groups was the f a t % t e s t in the milk of the f i r s t 50 days of the subsequent l a c t a t i o n (Table 20). The cows i n health code 1 had the higher f a t t e s t (3.84% versus 3.62%). Cows in health code group 2 l o s t more weight in the e a r l y post partum period of the current l a c t a t i o n and they also l o s t more weight i n the subsequent e a r l y post partum period. In terms of mean production and the slopes f o r f a t %, milk and FCM, no d i f f e r e n c e s between health code groups reached a s i g n i f i c a n t ( P & . 0 5 ) l e v e l (Figure 6). Table 20: Means and standard d e v i a t i o n s of t r a i t s in the subsequent l a c t a t i o n and the d i f f e r e n c e s between the health code groups (health codes of the current 1 a c t a t i on). Health code 1 Health code 2 Tra i t X n s.d. X n s.d. Si BWC c a l v i n g - ( l ) to ca l v i n g - ( 2 ) (kg) 44 47 60.5 86 22 78.5 * Wt. at c a l v i n g (2) (kg) 674 47 61 674 21 65 n . BWC 0-60 days p.p. (kg) -56 38 33.4 -71 16 42.6 n . BWC 0-80 days p.p. (kg) -36 38 47.5 -63 1 6 35 .2 * BWC 60-80 d.p.p. (kg) 17 38 26.6 8 16 22.3 n . Fat % 0-50 d.p.p. 3.84 38 . 56 3. 62 18 .53 * S i g n i f i c a n t d i f f e r e n c e s : * P ; - .05, n . s . = not s i g n i f i c a n t (1) current c a l v i ng , (2) subsequent c a l v i n g - 56 - Figure 6: Mean production and slopes of health code group 1 and health code group 2 f o r f a t %, milk and f a t corrected milk (FCM) of the subsequent 1 a c t a t i on (0-150 days ) . 'Health code 1 Health code 2 0 50 100 150 days of subsequent l a c t a t i o n - 57 - 4.5.3. Influence of season The c a l v i n g season of the current l a c t a t i o n i n - fluenced the onset of the l a c t a t i o n in the subsequent l a c t a t i o n (Table 21, Figure 7). The milk production of the cows c a l v i n g during the pasture season in the current l a c t a t i o n increased f a s t e r than the production of cows c a l v i n g during the non-pasture season in the current l a c t a t i o n . In terms of t o t a l milk production or FCM production in the f i r s t 150 days of the subsequent l a c - t a t i o n , there were no s i g n i f i c a n t (P> .05) d i f f e r e n c e s between the two seasons. Table 21: Means and standard d e v i a t i o n s of t r a i t s in the subsequent l a c t a t i o n influenced by the c a l v i n g season of the current l a c t a t i o n . Trai t Slope milk 0-50 d.p.p. Slope f a t % 0-50 d.p.p. Slope FCM 0-50 d.p.p. Pasture season x n s.d Non nPasture season x n s.d. Sign 2125 26 .1108 .1115 31 .1921 ** 0090 23 .0135 .0042 29 .0100 n.s 1679 23 .1187 .0939 29 .1813 * S i g n i f i c a n t d i f f e r e n c e s : * P&.05, ** P*.01 n.s. = not s i g n i f i c a n t d.p.p. = days post partum <- 58 - Figure 7: Mean production and slopes of f a t %, milk and f a t corrected milk (FCM) of the subsequent l a c t a t i o n (0-150 days). Differences due to the c a l v i n g season of the current l a c t a t i o n . Pasture season Non-Pasture season 0 50 100 150 days of subsequent l a c t a t i o n - 59 - 4.6. Average d a i l y milk production over the two l a c t a t i o n s The analyses of the milk production showed that the l a t e bred cows produced more milk and FCM in both the current and the beginning of the subsequent l a c t a t i o n . The longer i n t e r v a l from p a r t u r i t i o n to conception of the l a t e bred group also r e s u l t e d i n a longer dry period. In order to compare the d a i l y milk production of the e a r l y and the l a t e bred group, the health status groups and the groups according to the c a l v i n g season, the average d a i l y milk production from the beginning of the current to day 150 of the subsequent l a c t a t i o n was c a l c u l a t e d . The r e s u l t s of t h i s c a l c u l a t i o n showed that there were no d i f f e r e n c e s i n the average d a i l y milk and FCM production between e a r l y and l a t e bred groups, health status groups or groups according to c a l v i n g season (Table 22). These r e s u l t s demonstrated that there was no s u p e r i o r i t y of the l a t e bred group in terms of milk production.when the longer dry period (due to more days open) was taken into account. - 60 - Table 22: Average d a i l y milk and FCM production from beginning of the current l a c t a t i o n to day 1 of the subsequent l a c t a t i o n . T r a i t Early bred group x n s.d Late bred group x n s.d milk (kg) 22.11 133 5.07 FCM (kg) 20.69 33 5.64 22.79 20.63 38 38 5.65 6.00 Health code group 1 Health code group 2 n s.d. milk (kg) 22.66 FCM (kg) 20.68 49 5.15 49 5.96 Pasture season x n s.d. x 22.05 20.62 n 22 22 s.d. 5 .90 5.54 Non-Pasture season x n s.d. milk (kg) 23.73 32 5.00 21.44 39 5.49 FCM (kg) 21.64 32 6.15 19.86 39 5.44 n.s. = not s i g n i f i c a n t (P>.05) - 61 - 4.7. C o r r e l a t i o n s and regressions The complete c o r r e l a t i o n tables are presented in the Appendix (Tables 6 to 9). 4.7.1 . C o r r e l a t i o n s between reproductive t r a i t s The f i r s t v i s u a l l y detected heat was c o r r e l a t e d with the f i r s t progesterone detected heat and with the days from p a r t u r i t i o n to the f i r s t s e r v i c e (Table 23). The f i r s t progesterone detected heat was h i g h l y c o r r e l a t e d with the duration of the f i r s t estrous c y c l e . The l a t e r the f i r s t progesterone heat was detected, the longer was the duration of the f i r s t estrous c y c l e . In terms of milk progesterone l e v e l s , t h i s i n d i c a t e d that milk progesterone l e v e l s were high f o r a long time p r i o r to a l a t e detection of the f i r s t progesterone heat (see d e f i n i t i o n of duration of f i r s t estrous c y c l e , page 27). The f i r s t c y c l e length was not c o r r e l a t e d with the f i r s t v i s u a l l y detected heat. The remaining s i g n i f i c a n t c o r r e l a t i o n s l i s t e d in Table 23 were cause r e l a t i o n s : days to f i r s t s e r v i c e were c o r r e l a t e d with days open and the c a l v i n g i n t e r v a l . The number of s e r v i c e s per conception were c o r r e l a t e d to days open, to the i n t e r v a l from the f i r s t s e r v i c e to conception and to the c a l v i n g i n t e r v a l . - 62 - Table 23: C o r r e l a t i o n s between reproductive, t r a i t s of the current post partum period. 1st vi si bl e heat 1st prog, heat 1st cycle 1ength days to 1st service number of services .'days •open Days 1st service to conception 1st visible heat 1.00 1st prog, heat .32* 1.00 1st cycle length .19 .62* 1.00 Days 1st service .33* .03 .04 1.00 # of services -.11 -.01 -.07 .05 1.00 Days open .06 -.01 -.04 .55* .77* 1.00 Days to 1st serv. to conception -.13 -.01 -.06 .05 .90* .86* 1.00 Calving interval .07 .03 -.01 .59* .69* .96* .80* * S i g n i f i c a n t c o r r e l a t i o n ( P & .01) Table 2.4: C o r r e l a t i o n s between reproductive and productive t r a i t s of the current l a c t a t i o n . 1st cycle .-length days _to "1st s e r v i c e . number of serv i c e s days open c a l v i n g i nterva FCM 0-50 days . 26** .15 .18 .15 .13 FCM 50-100 days .24* . 20 .21* . 1 9 .18 Milk 305 days .17 .36** . 34** . 39** .36** FCM 305 days .18 . 30** . 37** .37** . 37** Slope milk 305 d, . . 04 . 1 3 2g** . 32** .36** Slope FCM 305 d. .04 .13 2 9** . 32** . 37** S i g n i f i c a n t c o r r e l a t i o n s * P ^ .05, ** p .01 - 63 - 4.7.2. C o r r e l a t i o n s betweeen reproductive and productive t r a i t s of the current l a c t a t i o n The f i r s t c y c l e length was p o s i t i v e l y c o r r e l a t e d with the FCM production of the f i r s t and second 50 days of the current l a c t a t i o n (Table 24). The i n t e r v a l from c a l v i n g to f i r s t s e r v i c e was p o s i t i v e l y c o r r e l a t e d with the t o t a l milk and FCM production of the current l a c t a t i o n . The number of s e r v i c e s per conception was p o s i t i v e l y c o r r e l a t e d with milk and FCM production f o r the period 50-100 days, the e n t i r e l a c t a t i o n , as 'well as with the slopes f o r milk and FCM production of the e n t i r e l a c t a t i o n . The number of s e r v i c e s per conception, days open and the c a l v i n g i n t e r v a l were p o s i t i v e l y c o r r e l a t e d with the t o t a l milk and FCM production of the current l a c t a t i o n and with the slopes of the 305 day milk and FCM production. These c o r r e l a t i o n s i n d i c a t e d that the l a t e r the cows conceived, the more they produced or v i c e - v e r s a . 4.7.3. C o r r e l a t i o n s between reproductive t r a i t s of the current and productive t r a i t s of the subsequent l a c t a t i o n The f i r s t progesterone detected heats were s i g n i f - i c a n t l y c o r r e l a t e d with the FCM production of the 50 to 100 days period of the subsequent l a c t a t i o n and with the slope of the f a t t e s t of the. f i r s t 150 days in the sub- sequent l a c t a t i o n (Table 25). The f i r s t estrous cycle length i n the current l a c t a t i o n was s i g n i f i c a n t l y cor- - 64 - r e l a t e d with the f a t t e s t i n the f i r s t 50 days of the subsequent l a c t a t i o n and with the slope of the f a t t e s t and the FCM production i n the f i r s t 150 days of the subsequent l a c t a t i o n . Days from p a r t u r i t i o n to f i r s t s e r v i c e , days open and the c a l v i n g i n t e r v a l were c o r r e l a t e d with several production t r a i t s i n the subsequent l a c t a t i o n . In order to explain these c o r r e l a t i o n s , a regression a n a l y s i s was conducted, the r e s u l t s of which w i l l be discussed below. Table 25: C o r r e l a t i o n s between reproductive t r a i t s of the current and productive t r a i t s of the subsequent l a c t a t i o n . 1st 1st days days c a l v i n g T r a i t prog. c y c l e to 1st "" J/ i n t e r v a l heat length s e r v i c e o p e n i n t e r v a l Fat % 0-50 days .18 .41** -.12 -.06 -.07 FCM 50-100 days .33** .25 .32** .43** .28* FCM 100-150 days .13 .11 .29* .40** .34** SI ope mi 1k 0-150 days .06 -.21 .37** .39** .35** Slope f a t % 0- 150 days -.34** -.34** -.04 -.14 -.10 Slope FCM 0-150 days -.23 -.54** .30* .23 .22 S i g n i f i c a n t c o r r e l a t i o n s : * P * .05, ** P ^ .01 - 65 - 4.7.4. C o r r e l a t i o n s between reproductive t r a i t s and body weight changes i n the current and subsequent 1 acta t i on The f i r s t v i s i b l e heat and the f i r s t progesterone detected heat were both p o s i t i v e l y c o r r e l a t e d with the body weight changes in the f i r s t 60 and 80 days respec- t i v e l y of the current l a c t a t i o n (Table 26). The negative c o r r e l a t i o n c o e f f i c i e n t i n d i c a t e d that the more weight a cow l o s t in the e a r l y post partum period the l a t e r the onset of estrus and the l a t e r the cow showed a v i s i b l e estrus behaviour. Since l a t e onset of estrus and estrus behaviour delayed the f i r s t s e r v i c e , days to f i r s t s e r v i c e was c o r r e l a t e d with the e a r l y l a c t a t i o n body weight changes in the same manner as the f i r s t progesterone and the f i r s t v i s u a l l y detected heat. Days open and the c a l v i n g i n t e r v a l were not c o r r e l a t e d with body weight changes in e i t h e r l a c t a t i o n . The f i r s t progesterone detected heat and the days to the f i r s t s e r v i c e were both ne g a t i v e l y c o r r e l a t e d with the 0-60 day weight changes in the subsequent l a c t a t i o n , i n d i c a t i n g that the l a t e r the onset of progesterone detected estrus and the l a t e r the f i r s t insemination took place, the more weight the cows l o s t in the e a r l y portion of the subsequent l a c t a t i o n . Early post partum body weight changes were c o r r e l a t e d with production t r a i t s (Appendix Table 9). C o r r e l a t i o n s with production t r a i t s and body weight changes can be explained better i f the c o r r e l a t i o n s between body weight changes and production are taken i n t o account. - 66 - Table 26: C o r r e l a t i o n s between reproductive t r a i t s and body weight changes (BWC) in the current and subsequent 1actation . 1st 1st days to d T r a i t (kg) v i s i b l e prog. 1st heat heat s e r v i c e Current l a c t a t i o n : BWC 0-60 days p.p. BCW 0-80 days p.p. BWC 60-80 days p.p. BWC 1st c a l v i n g to 2nd c a l v i n g Subsequent l a c t a t i o n BWC 0-60 days p.p. BWC 0-80 days p.p. BWC 60-80 days p.p. S i g n i f i c a n t c o r r e l a t i o n s : * P ^ .05, ** P ^. .01 d.p.p. = days post partum .24* -.24** -.20 -.19 .26** -.19 - .24* -.15 .06 -.01 .06 .05 .19 -.13 .01 .01 .07 -.26* -.25* -.17 -.03 -.21 -.21 -.03 .08 .00 .03 - .05 - 67 - 4.7.5. Test of i n f l u e n c e of days open on production in the subsequent l a c t a t i o n The a n a l y s i s of variance showed that the groups ( e a r l y and l a t e breeding) did not have a marked i n f l u e n c e on the production and body weight changes of the e a r l y subsequent l a c t a t i o n . The hypothesis i s that f a c t o r s other than the days from p a r t u r i t i o n to the f i r s t s e r v i c e , l i k e days open or the c a l v i n g i n t e r v a l , have a greater i n - fluence on the subsequent l a c t a t i o n . In order to show these i n f l u e n c e s , a simple regression a n a l y s i s was computed with days open as independent continuous v a r i a b l e . This a n a l y s i s r e s u l t e d in the f o l l o w i n g observations: Days open contributed s i g n i f i c a n t l y to the p r e d i c t i o n of milk and FCM production i n the f i r s t l a c t a t i o n (Table 27). In the subsequent l a c t a t i o n days open of the current l a c t a t i o n influenced the weight of the c a l f in the subsequent l a c t a t i o n but not the body weight changes in the e a r l y post partum period of the subsequent l a c t a t i o n . The c o n t r i b u t i o n of days open to the p r e d i c t i o n of production t r a i t s in the e a r l y subsequent l a c t a t i o n was moderate. Days open influenced the slope of the milk production curve in the f i r s t 150 days but neither the slope of f a t % or FCM production was i n f l u e n c e d . The regression of milk production during the f i r s t 50 days versus days open was not s i g n i f i c a n t , the regression of days open on FCM production from 1 00-1 50 days, however, was s i g n i f i c a n t . - 68 - Table 27: Results of the simple regression analyses with days open as independent continuous v a r i a b l e . Dependent v a r i a b l e s Current l a c t a t i o n : Milk 305 days FCM 305 days (kg) Subsequent l a c t a t i o n : Wei ght of ca1f (kg) Weight change 0-60 d.p.p. (kg) Weight change 60-80 d.p.p. (kg) Milk 0-50 days (kg) FCM 100-150 days SI ope milk 0-150 days Slope f a t % 0-150 days Slope FCM 0-150 days Regression c o e f f i c i e n t 19.3376 14.2039 - . 07694 -.31395 .07309 1 . 77031 2.0541 1 . 000420 - .000021 .000230 C o e f f i c i ent of deter- mination R2 .19 .14 . 57 .03 .00 .05 .16 .15 .02 .05 Sign n.s. n.s. n.s, * n. s n . s * S i g n i f i c a n t c o n t r i b u t i o n to the regression equation ( P * . 0 1 ) . n.s. = ' not s i g n i f i c a n t BWC = body weight changes, d.p.p. days post partum - 69 - 5. DISCUSSION 5.1. The onset of the estrous c y c l e , v i s u a l and progesterone detected heat The i n v o l u t i o n of the bovine uterus a f t e r p a r t u r i t i o n takes approximately 30 days (Lamming , 1 978 ; Roberts, 1971). The f i r s t progesterone r i s e was reported by Lamming (1978) to occur 25 ± 10 days post partum. The r e s u l t s of t h i s study i n d i c a t e d that the f i r s t progesterone detected heat occurred 33 ± 10 days with a range from 19 to 78 days post partum and are comparable with the f i n d i n g s of Morrow et a l . (1969). He reported that the f i r s t estrus was between 30 and 76 days post partum, and that f o l l i c u l a r development s t a r t e d between 16 and 21 days post partum. In i n d i c a t i n g i t h e wide range from 30 to 76 days Morrow et al . ( 1 969 ) stressed the importance of the i n d i v i d u a l cow. The wide range in the onset of the f i r s t progesterone heat also showed that the wide range of the dete c t i o n of the f i r s t v i s i b l e heat (8 to 127 days) was not only a r e s u l t of inadequate observation of the cows but that there a c t u a l l y was a large v a r i a t i o n between cows. De K r u i f (1978) included chance inhhis l i s t of f a c t o r s i n f l u e n c i n g the f e r t i l i t y of d a i r y herds. He concluded that i n small herds (up to approximately 40 cows) due to the large v a r i a t i o n between i n d i v i d u a l cows the f e r t i l i t y by chance ( f o r no apparent reason) may be impaired. D i f f e r e n t i n t e r v a l s to the f i r s t estrus have been reported by King - 70 - et al . ( 1 976 ) with 19.5 days, Mather et a l . ( 1 978) with 21 days and Wagner and Hansel (1969) with 14 days. The time d i f f e r e n c e between the f i r s t progesterone detected heat and the f i r s t v i s i b l e heat (16 days) i n d i c a t e d that most of the f i r s t heats were s i l e n t or with l i t t l e behavioural evidence, t h e r e f o r e , they remained undetected by the herdsmen. Early post partum heats are reported to be d i f f i c u l t to detect v i s u a l l y (Davi>d et al . , 1971; Morrow et a l . , 1969; King et a l . , 1976). The time from p a r t u r i t i o n to the f i r s t progesterone detected estrus (33 days)-was s i m i l a r to the f i n d i n g s of Callahan et a l . (1971) and King et a l . (1976). These workers observed the herds continuously and did not f i n d any d i f f e r e n c e between the occurrence of the f i r s t progesterone detected and the f i r s t v i s u a l detected heats. F i r s t estrous cycles were reported to vary considerably in length and very often were shorter than 21 days (Mather et a l . , 1978; B r i t t , 1980), therefore the average duration of 17 days found in t h i s experiment can be considered normal. A l - though B r i t t (1980) excluded a l l the cows with c a l v i n g associated reproductive d i s o r d e r s , he found an average f i r s t cycle length of 17 days as w e l l . In t h i s study the f i r s t progesterone detected heats were s i g n i f i c a n t l y c o r r e l a t e d (r = .62) with the f i r s t c ycle lengths. The l a t e r the f i r s t progesterone detected estrus occurred, the longer was the duration of the preceeding estrous - 71 cycle (see d e f i n i t i o n of f i r s t estrous c y c l e , page 27) Mather et a l . (1978) found a p o s i t i v e c o r r e l a t i o n between the f i r s t progesterone peak l e v e l post partum and the duration of the f i r s t c y c l e . He also found an increase in the peak progesterone concentration and in the cycle length over the f i r s t three cycles before the system was back to steady progesterone cycles and normal cy c l e lengths.^ B r i t t (1980) reported average cycle lengths of 21.1 and 21.4 days f o r subsequent cycles which followed a f i r s t cycle length of 17 days. Calving problems or c a l v i n g associated e a r l y post partum reproductive problems did not in f l u e n c e the onset of the progesterone detected estrous c y c l e s in t h i s study. Baier et a l . (1973) reported that a l a t e r onset of the estrous cycle i n cows with c a l v i n g associated problems was mostly r e l a t e d to a slower i n v o l u t i o n of the uterus. Baier et a l . (1973) observed the cows f o r estrus signs and used r e c t a l palpations to check uterine i n v o l u t i o n and f o l l i c u l a r development. The c a l v i n g season did not in f l u e n c e the onset of the estrous cycle or the f i r s t c ycle length. S t o t t and 1 The pattern of the milk progesterone concentration of the f i r s t and subsequent estrous cycles of the same cows i n the same experiment are being studied in a d i f f e r e n t Master of Science p r o j e c t by W.L. Slack, Department of Animal Science, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C. - 72 - Williams (1962) showed that cows exposed to high temp- eratures in the summer months had depressed f e r t i l i t y . They r e l a t e d the lower f e r t i l i t y to very long estrous c y c l e s . The pasture season temperatures i n the temperate Fraser Valley climate apparently were not high enough to inf l u e n c e the cycle lengths of the cows. The f a c t that neither c a l v i n g associated reproductive problems, the c a l v i n g season, nor' the c o v a r i a b l e s (age, milk production 0-50 days, body weight changes 0-60 days) accounted f o r a s i g n i f i c a n t part of the v a r i a t i o n of the onset of estrus was an obvious expression of the large i n e x p l a i n - able v a r i a t i o n between i n d i v i d u a l cows. 5.2. Days from p a r t u r i t i o n to the f i r s t s e r v i c e , number of ser v i c e s per conception, days open and the c a l v i n g i n t e r v a l The early bred group sconceivirig-88 days post partum a f t e r 1.50 services per conception as opposed to the l a t e bred group conceiving 120 days post partum a f t e r 1.96 serv i c e s per conception showed a p o s i t i v e e f f e c t of the e a r l i e r breeding on f e r t i l i t y in t h i s herd. A number of cows scheduled to be bred at the f i r s t v i s i b l e heat f o l l o w i n g 50 days post partum did not show any v i s i b l e heat u n t i l much l a t e r . Therefore, the average i n t e r v a l from the scheduled breeding to the actual breeding was longer in the e a r l y bred group (50 to 73 days = 23 days) than in the l a t e bred group (80 to 93 days = 13 days). - 73 - In comparison to the l i t e r a t u r e , i n t e r v a l s from c a l v i n g to the f i r s t s e r v ice of 73 days and from c a l v i n g to conception of 88 days were not considered short and were necessary to achieve a one year c a l v i n g i n t e r v a l (Ayalon et a l . , 1971; Bar-Anan and S o l l e r , 1979; Machnai and K a l i , 1971). Many authors have reported that the conception rate from serv i c e s p r i o r to 40 days post partum was lower than conception from serv i c e s between 50 and 70 days or l a t e r in the post partum period ( K r a u s s l i c h , 1974; Kupferschmid, 1975). The same workers also reported that there was no d i f f e r e n c e i n conception rate of inseminations between 50 and -70 days as compared to se r v i c e s l a t e r in the post partum period. S i g n i f i c a n t l y increased numbers of se r v i c e s per conception 80 days post partum or l a t e r , as found in t h i s experiment, have not been reported o p r e v i o u s l y . The s i g n i f i c a n t d i f f e r e n c e between the e a r l y bred group and the l a t e bred group i n terms of number of ser v i c e s per conception and days from f i r s t s e r v i c e to conception was eliminated when cows with c a l v i n g associated problems were excluded from the a n a l y s i s . This a n a l y s i s showed that cows in the e a r l y bred group conceived a f t e r 1.53 s e r v i c e s and that cows in the l a t e bred group conceived a f t e r 1.73 s e r v i c e s . This s t i l l showed a better f e r t i l i t y in the e a r l y bred group but the d i f - ference was no longer s i g n i f i c a n t . Problem cows in the - 74 - e a r l y bred group conceived as r e a d i l y as the healthy cows (1.42 versus 1.53 s e r v i c e s per conception). Problem cows in the l a t e bred group required s i g n i f i c a n t l y more service s per conception than healthy cows in the same group (2.46 versus 1.73) and also required more se r v i c e s per conception than a l l other cows in the experiment (2.46 versus 1.60). These f a c t s can not be r e a d i l y explained in the context of t h i s study and need f u r t h e r i n v e s t i g a t i o n . Possible reasons were: the s e v e r i t y of the disorders of the a f f e c t e d cows might have been d i f - f e r e nt in the two groups; or treatment and treatment e f f e c t s might have been d i f f e r e n t . Onset of e s t r u s , length of the f i r s t estrous cycle and the number of v i s u a l l y and progesterone detected heats were the same f o r normal and problem cows. These f a c t s i n d i c a t e d that the reason for delayed conception was not due to ovarian i n a c t i v i t y . More l i k e l y the uterus was not ready f o r the implantation of the fertilized.-ovum at the time of the unsuccessful inseminations. Morrow et al . ( 1 969 ) reported that ovarian a c t i v i t y . a f t e r p a r t u r i t i o n normally resumed before uterine i n v o l u t i o n was completed. Baier et a l . (1973) reported that c a l v i n g d i f f i c u l t i e s delayed u t e r i n e i n v o l u t i o n . Retained placenta and m e t r i t i s also are known to be adverse to the implantation of the embryo (Roine and Saloniemi, 1978). - 75 - The seasonal influences on f e r t i l i t y were only s i g n i f i c a n t w i t h i n the l a t e bred group. Cows which calved in the pasture season had a decreased f e r t i l i t y . These f i n d i n g s again showed that in the l a t e bred group the apparent optimal time f o r insemination was passed so that influences l i k e season and health problems became s i g n i f i c a n t . Braun (1977) was able to improve the f e r t i l i t y in problem herds by breeding a l l cows i n those herds as soon as they showed normal estrous c y c l e s . Braun (1977) monitored the cycles with milk progesterone a n a l y s i s . Zerobin (1979) recommended breeding problem cows as soon as they show estrus ( e i t h e r v i s u a l or: : progesterone detected ones). His recommendation was based on the b e l i e f that an unsuccessful insemination did not influ e n c e the conception rate of subsequent breedings. A low f e r t i l i t y rate during l a t e summer and f a l l months was reported by Hewett (1968) and De K r u i f (1975). The lower f e r t i l i t y i n the pasture season also might have been associated with the body weight changes in the ea r l y post partum period. Cows which<calved 'in•the pasture season s t i l l l o s t weight between 60 and 80 days post partum while cows which calved in the non-pasture season were already gaining weight in the same period. Kingret al . ( 1 976) and Youdan and King ( 1 977 ) reported - 76 - a b e n e f i c i a l i n f l u e n c e of body weight gain on f e r t i l i t y at time of insemination. The goal of a one year c a l v i n g i n t e r v a l was achieved in the e a r l y bred group (373 days) but not in the l a t e bred group (404 days). These f i n d i n g s support the statement of Ayalon et a l . (1977) that in order to achieve a 365 day c a l v i n g i n t e r v a l , i t i s necessary to s t a r t breeding the cows not l a t e r than 50 days post partum. 5.3. The r e l a t i o n s h i p between reproduction, production and body weight changes The dai r y herd of the A g r i c u l t u r e Canada Research S t a t i o n in Agassiz i s a high y i e l d i n g H o l s t e i n herd (average production of the 85 cows in t h i s experiment: 8084 kg milk, 7644 kg FCM). S i m i l a r studies dated 10 to 20 years ago dealt with production l e v e l s which were s u b s t a n t i a l l y lower (Smith and Legates, 1962; Wilton et al . 1 967 ). More recent s t u d i e s , e s p e c i a l l y from I s r a e l , have involved milk production l e v e l s comparable with the production of the Agassiz herd. Beside the genetic improvement of the herds, n u t r i t i o n and management have been improved s u b s t a n t i a l l y to increase milk production, yet r e s u l t i n g in more st r e s s on the cows. For t h i s reason the r e s u l t s in t h i s study of reproduction-production r e l a t i o n s h i p s have been compared to research r e s u l t s from I s r a e l . S i g n i f i c a n t c o r r e l a t i o n s in the range of r = .30 - 77 - between milk production and reproduction t r a i t s (number of serv i c e s per conception, days open, c a l v i n g i n t e r v a l ) have been reported p r e v i o u s l y (Bar-Anan and S o l l e r , 1979; Francos and Rattner, 1975; Hewett, 1968). These c o r r e l a - tions o f f e r an explanation f o r the higher 305 day milk y i e l d of the l a t e bred group. The f a c t that e a r l y l a c t a - t i o n milk y i e l d s were not s i g n i f i c a n t l y c o r r e l a t e d with reproduction t r a i t s but the slopes f o r milk production of the l a t t e r part of the current l a c t a t i o n of cows in the l a t e bred group showed a greater persistency i n d i c a t e d that the d i f f e r e n c e s in milk y i e l d between the two groups were mainly due to the d i f f e r e n c e s in the l a t t e r part of the l a c t a t i o n . These f i n d i n g s are in agreement with the f i n d i n g s of Erb et a l . (1952) and Smith and Legates (1962) who concluded that gestation did not m a t e r i a l l y a f f e c t milk y i e l d u n t i l the 5th month a f t e r conception. The higher milk production in the l a t e bred group was not accompanied by a greater body weight loss in the e a r l y post partum period. The tendency to a higher 305 day milk production of cows c a l v i n g during the pasture season was accompanied by s i g n i f i c a n t l y (P6.01) higher body weights at c a l v i n g and body weight changes i n the e a r l y post partum period as well as with a lower f e r t i l i t y ( P ^ . 0 5 ) . These s i t - uations i n d i c a t e d that high milk y i e l d s were not n e c e s s a r i l y r e l a t e d to high body weight losses in the e a r l y post partum period. However, high body weight - 78 - losses often were r e l a t e d to high milk y i e l d s and with depressed f e r t i l i t y . S i m i l a r f i n d i n g s and the repeatedly reported negative influence of e a r l y post partum body weight losses on f e r t i l i t y (Amir and K a l i , 1974; B r o s t e r , 1973; Youdan and King, 1977) i n i t i a t e d the work of Herz and Graf (1976) and Roberts et a l . (1979a) (1979b). Herz and Graf (1976) did not f i n d that blood glucose l e v e l s had any i n f l u e n c e on f e r t i l i t y . Roberts et a l . (1979a) 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 f a t t y l i v e r (due to the m o b i l i z a t i o n of f a t t y acids from adipose t i s s u e in the e a r l y post partum period) and f e r t i l i t y . The f i n d i n g s of Roberts et al . ( 1 979a) offered an explanation for lower f e r t i l i t y of cows which calved during the pasture season and were s t i l l l o s i n g weight in the period 60 to 80 days post partum. On the average, the f i r s t insemination took place 83 days post partum. Cows which calved during the non-pasture season had a better f e r t i l i t y than cows which calved during the pasture season and were already gaining weight between 60 and 80 days post partum. A p o s i t i v e e f f e c t of body weight gain on f e r t i l i t y was reported by Hodges (1976), Huth and Smidt (1979) and Youdan and King (1977). A f u r t h e r explanation f o r the better f e r t i l i t y of cows c a l v i n g in the winter months (non-pasture season) i s the reported lower progesterone l e v e l s during estrus in the winter months which were r e l a t e d to increased - 79 - conception rates (Rosenberg et a l . 1977). The longer rest period post partum of the l a t e bred group r e s u l t e d i n a longer dry period and therefore in a higher weight gain between c a l v i n g s , a higher body weight at the subsequent c a l v i n g , . a n d a heavier c a l f . The l a t e bred group also gained weight at a higher d a i l y rate (from 60 and 80 days post partum r e s p e c t i v e l y to the subsequent c a l v i n g ) than the e a r l y bred group. The weight gain between calvings i s e s p e c i a l l y important f o r h e i f e r s , t h e r e f o r e , several authors recommended a longer rest period for h e i f e r s than f o r cows (Louca and Legates 1 968 ; Bar-Anan and S o l l e r , 1979). Calving associated disorders were not s i g n i f i c a n t l y r e l a t e d to production t r a i t s , the s l i g h t l y higher (PA.10) FCM production observed in a f f e c t e d cows can be explained with t h e i r longer i n t e r v a l from c a l v i n g to conception ( c o r r e l a t i o n between days open and 305 day FCM production fo r a l l cows in the experiment r = .37). The carryover e f f e c t s of the current l a c t a t i o n to the subsequent l a c t a t i o n were moderate. The greater p e r s i s t - ency of milk production in the f i r s t 150 days of the subsequent l a c t a t i o n f o r the l a t e bred group can be re- l a t e d to the longer dry period of t h i s group. A l l the cows in the experiment were dried o f f at 305 days which r e s u l t e d in a longer dry period f o r the l a t e bred group. Wood (1977) showed that the dry period influenced the - 80 - onset of milk production in the f o l l o w i n g l a c t a t i o n . Due to the longer dry period of the l a t e bred group the average d a i l y milk and FCM y i e l d s ( c a l c u l a t e d over both l a c t a t i o n s ) were the same f o r both the e a r l y and the l a t e bred group. Economically the average production per day of productive l i f e i s more important than the 305 day l a c t a t i o n y i e l d s . Therefore, as mentioned before, I s r a e l introduced a system which adjusts l a c t a t i o n milk y i e l d s for days open (Bar-Anan and S o l l e r , 1979). The cows with c a l v i n g associated reproductive problems (health code group 2) had heavier calves at both c a l v i n g s . There was no d i f f e r e n c e in body weights at c a l v i n g s between the two health code groups. P h i l i p s s o n (1976) found that the d i f f e r e n t weights of calves from cows with equal body weights (w i t h i n the same breed) were due to a) the age of the cow and b) genetics. The incidence of c a l v i n g associated reproductive problems of the 71 cows c a l v i n g a second time w i t h i n t h i s experiment was very low (5 o b s e r v a t i o n s ) ; too low to include i t i n t o the s t a t i s t i c a l a n a l y s i s . This low incidence of c a l v i n g associated problems might be due to the f a c t that at the subsequent c a l v i n g s there were no h e i f e r s c a l v i n g because new cows were not introduced i n t o t h i s experiment. At the current c a l v i n g there were 10 h e i f e r s , which represented 40% of the cows with c a l v i n g associated problems. P h i l i p s s o n (1976) showed that the incidence of d y s t o c i a - 81 was higher in primiparous than in multiparous cows in Swedish dai r y breeds. Cows in health code group 2 had a lower f a t t e s t in the f i r s t 50 days of the subsequent l a c t a t i o n . Their f a t t e s t tended to be lower in the current l a c t a t i o n as w e l l ; however, the d i f f e r e n c e was not s i g n i f i c a n t . Whether t h i s d i f f e r e n c e in the f a t t e s t was g e n e t i c a l l y determined or was r e l a t e d to the repro- ductive disorders cannot be decided in the context of t h i s s tudy. Cows which calved during the pasture season at the beginning of the current l a c t a t i o n showed a f a s t e r increase of the d a i l y milk y i e l d (slope f o r milk 0-50 days) and a lower f a t t e s t in the f i r s t 50 days of the subsequent l a c t a t i o n . Since 90% of the cows calved in the same season at the subsequent c a l v i n g as at the current c a l v i n g , these d i f f e r e n c e s can be associated with the c a l v i n g season. Wood (1969) showed that the production of cows which calved in spring and e a r l y summer increased f a s t e r than f o r cows which calved in other seasons. Huber et a l . (1964) and Waite et a l . (1959) reported that a marked milk f a t depression occurred e s p e c i a l l y during spring pasture. A l l these workers dealt with spring and ea r l y summer c a l v i n g s . The pasture season in t h i s experiment, however, covered the complete pasture season, May to October. Hence, the f i n d i n g s of Wood (1969), Huber et a l . (1964) and Waite et a l . (1959) do not c o n c l u s i v e l y explain - 82 - the r e s u l t s in t h i s experiment. The regression equations to p r e d i c t body weight changes and production in the e a r l y subsequent l a c t a t i o n did not reveal any new r e l a t i o n s h i p s . Days open was a s u i t a b l e parameter to p r e d i c t the weight of the c a l f of 9 the subsequent c a l v i n g (R = . 5 7 ) . In other equations, p r e d i c t i o n s of production t r a i t s in the subsequent l a c t a t i o n , with days open as independent v a r i a b l e ; the c o e f f i c i e n t of determination (R ) although s i g n i f i c a n t , was very low. The r e s u l t s of the regression a n a l y s i s showed again that the r e l a t i o n s h i p between reproductive t r a i t s of the current l a c t a t i o n and productive t r a i t s of the subsequent l a c t a t i o n were not s u b s t a n t i a l . - 83 - 6. SUMMARY AND CONCLUSIONS In a Ho l s t e i n d a i r y herd, the influ e n c e of e a r l y and l a t e breeding post partum on reproduction was i n v e s t i - gated. The e a r l y post partum reproductive a c t i v i t y was monitored with milk progesterone a n a l y s i s . The large v a r i a t i o n in the onset of the f i r s t e s t r u s , (both progesterone and v i s u a l l y detected ones) could not be explained by age, milk production, body weight losses during the e a r l y post partum pe r i o d , c a l v i n g associated reproductive d i s o r d e r s , or c a l v i n g season. The l a t e r d e tection of the f i r s t v i s i b l e heat as compared to the f i r s t progesterone detected heat i n d i c a t e d that most cows showed l i t t l e or no behavioural evidence of f i r s t e s t r u s , therefore they were not detected by the herdsmen. Cows bred e a r l y (73 ± 18 days post partum) conceived a f t e r fewer services per conception than cows bred l a t e (93 ± 17 days post partum). Within the e a r l y bred group cows with c a l v i n g associated reproductive problems con- ceived as r e a d i l y as unaffected cows, while a f f e c t e d cows in the l a t e bred group required s i g n i f i c a n t l y more se r v i c e s per conception. A s i m i l a r s i t u a t i o n was found in r e l a t i o n to the c a l v i n g season: Calving during the pasture season delayed conception in the l a t e bred group but did not influe n c e conception in the e a r l y bred group. The cows in the l a t e bred group produced more FCM in the 305 day l a c t a t i o n and in the beginning of the - 84 - subsequent l a c t a t i o n . There was no d i f f e r e n c e in the average d a i l y milk production c a l c u l a t e d ov/er the period from the beginning of the current to day 150 of the sub- sequent l a c t a t i o n . Days open and days dry become important f a c t o r s i f more emphasis i s placed on average milk y i e l d s per day of productive l i f e rather than on 305 day l a c t a t i o n y i e l d s . High milk production had a negative i n f l u e n c e on reproduction only when r e l a t e d to s u b s t a n t i a l body weight losses in the same time period. There was no marked e f f e c t of c a l v i n g associated problems or c a l v i n g season on production in the current or the beginning of the subsequent l a c t a t i o n . In short, the conclusions from t h i s study are: The onset of estrus showed a large i n e x p l a i n a b l e i n d i v i d u a 1 v a r i a t i o n . Early breeding versus l a t e breeding r e s u l t e d in less o i s e r v i c e s per conception f o r the e a r l y bred cows. Cows with reproductive problems conceived r e a d i l y when bred e a r l y but required more servi c e s per conception when bred l a t e . 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The e f f e c t of body weight changes on f e r t i l i t y during the post partum period i n d a i r y cows. B r i t . vet. J . 133: 635-641. Zamet, C. H., Colenbrander, V. F., Erb, R. E., Callahan, C. J . , Chew, B. P. and M o e l l e r , N. J . 1979. Var i a b l e s associated with peripartum t r a i t s in d a i r y cows. Theriogenology. 11: 229-272. Zerobin, K. 1979. Personal communications. Faculty of Veterinary Medicine. Z u r i c h . - 93 - 8. APPENDIX Table 1: Means and standard deviations of the covariables milk production 0-50 days post partum, body weight changes (BWC) 0-60 days post partum in the current l a c t a t i o n and age of c a l v i n g at the beginning of the current l a c t a t i o n . Cows i n: Mi 1 k Producti on 0-50 d.p.p. (kg) Body Weight Changes 0-60 d.p.p. (kg) Age (mb . ) X s.d. X s.d • X s.d • Early bred group 1 520 326 -40.8 37 . 1 44.9 20. 0 Late bred group 1653 380 -54.4 40. 9 46.2 22 . 7 Health code 1 1619 360 -40 .8 37. 1 45 .1 17. 3 Health code 2 1511 351 -54.4 40 . 8 46 .6 29 . 2 Pasture season 1649 336 -53.3 31 . 2 47.3 20. 9 Non-pasture season 1 543 374 -43.9 44. 9 44.4 21 . 5 Total 1587 358 -47.6 39. 4 45 .5 21 . 3 T a b l e 2 : M e a n s a n d s t a n d a r d d e v i a t i o n s o f r e p r o d u c t i v e t r a i t s i n t h e c u r r e n t l a c t a t i c a ) E a r l y a n d l a t e b r e d g r o u p s , h e a l t h s t a t u s g r o u p a n d g r o u p s a c c o r d i n q t o t h e c a l v i n g s e a s o n a ) T r a i t b ) I n t e r a c t i o n s a n d c o v a r i a b l e s G r o u p s ( G ) e a r l y b r e d l a t e b r e d H e a l t h s t a t u s ( H ) n o r m a l a b n o r m a l C a l v i n g s e a s o n ( S ) p a s t u r e n o n - p a s t u r e X s . d . X s . d . S i g n X s . d . X s . d . S i g n X s . d . X s . d . S i g n 1st v i s i b l e heat (d.p.p.) 50 2 8 . 5 4 7 2 5 . 2 n . s . 49 27.6 47 25.0 n.s. 49 28.3 48 25.8 n.s. 1st prog. det. heat (d.p.p. ) 3 4 10; 0 3 3 1 0 . . 5 n . s . 34 11.1 34 8.2 n.s. 32 8.6 35 11.4 n.s. Number of v i s i b l e heats 2 . 2 1 . 0 3 . 0 1 . . 7 ** 2.5 1.2 2.8 2.0 n.s. 2.5 1.1 2.7 1.7 n.s. Number of prog. det. heats 3 . 1 1 . 4 4 . 2 1 . 3 ** 3.7 1.4 3.7 1.6 n.s. 3.7 1.3 3.7 1.6 n.s. 1st cycle length (days) 1 8 . 4 8 . 6 1 6 . 6 6 . 2 n . s . 18.1 8.3 15.9 4.7 n.s. 17.4 4.5 17.6 9.2 n.s. Days to 1st. service 7 2 1 8 . 2 9 3 17 . 3 ** 82 21.5 83 18.9 n.s. 83 22.8 82 18.9 n.s. Number of services 1.50 1 . 9 5 * 1.63 1.96 * 1.74 1.72 n.s. Days from 1st service to conception 1 6 . 4 0 2 5 . 0 2 6 . 2 3 9 . 8 ** 18.7 29.9 27.9 40.9 ** 23.0 36.5 20.1 31.2 * Days open 8 8 3 3 . 0 1 2 1 4 0 . 6 * * 100 38 113 46 ** 106 42 103 39 * Calving Interval (days) 3 7 3 3 4 . 1 4 0 4 3 8 . 0 ** 385 35 400 47 ** 387 40 391 39 * I O b ) T r a i t N u m b e r o f p r o g . d e t . h e a t s 1 s t c y c l e l e n g t h ( d a y s ) N u m b e r o f s e r v i c e s D a y s f r o m 1 s t s e r v i c e t o c o n c e p t i o n D a y s o p e n C a l v i n g i n t e r v a l ( d a y s ) G x H n . s . n . s . I n t e r a c t i o n s G x S n . s . n . s . C o v a r i a b l e s mi 1 k BWC x S G x H x S a g e 0 - 5 0 0 - 6 0 ( m o . ) d.p.p.(tg) d . p . p . m ) * n . s . n . s . n . s . n . s . - . 0 0 4 5 1 ** n . s n . s . n . s . n . s . . 0 1 0 1 1 n . s . BWC n . s . n . s . n . s . n . s . n . s . * * n . s . n . s . n . s . n . s . n . s . n . s . n . s . n . s . 1 • n . s . n . s . n . s . n . s . s i g n i f i c a n t ( P * . 0 5 ) s i g n i f i c a n t ( P * . 0 1 ) n o t s i g n i f i c a n t b o d y w e i g h t c h a n g e s , d . p . p . = d a y s p o s t p a r t u m [ r a i t s l i s t e d i n T a b l e 2 a w i t h o u t a n y s i g n i f i c a n t i n t e r a c t i o n s a n d c o v a r i a b l e s w e r e n o t l i s t e d i n T a b l e 2 b . Table 3: Means and standard deviations of productive traits in the current lactation a) Early and late bred groups, health status group and groups according to the calving season b) Covariables1 Groups (G) Health status (H) Cal vi ng season (S) Trait early bred late bred normal abnormal pasture non-pasture X s.d. X s.d. Sign. X s.d. X s.d. Sign. X s.d. X s.d. Si gn FCM 0-50 days (kg) 1401 310 1509 416 n. s. 1495 354 1362 371 n .s. 1532 33~5 1404 385 n.s. FCM 50-100 days (kg) 1386 285 1412 612 n. s. 1453 331 1269 709 n, s. 1458 335 1361 565 n.s. FCM 100-150 days (kg) 1284 233 1313 303 n. s, 1302 274 1293 265 n, . s. 1322 292 1288 251 n.s. FCM 305 days (kg) 7276 1565 7995 2304 * 7708 1974 7492 2089 * 7880 2012 7506 1992 * Milk 305 days (kg) 7595 1659 8550 2484 * 8084 2058 8084 2438 n. s. 8202 2082 8039 2250 n.s. Fat I 305 days 3.71 .47 3.57 .38 n. s. 3.68 .42 3.55 .44 n. s. 3.74 .46 3.57 .40 n.s. Slope milk 0-150 days -.0271 .0366 -.0372 .0639 n. s. -.0383 .0410 .0175 .0712 n. . s. -.0411 .0379 -.0249 .0609 n.s. Slope fat X 0-150 days -.0013 .0034 -.0016 .0036 n. s. -.0013 .0032 .0019 .0041 n. . 5 . -.0012 .0035 -.0019 .0035 n.s. Slope FCM 0-150 days -.0290 .0420 -.0405 .0648 n . s. -.0398 .0446 .0230 .0733 n. . S . -.1433 .0413 -.0287 .0632 n.s. Slope milk 150-305 days • -.1178 .0487 -.0955 .0448 ** -.1073 .0490 .1052 .0457 n. . s. -.1045 .0547 -.1079 .0419 n.s. Slope fat t 150-305 days .0009 .0008 .0010 .0119 n. s. -.0010 .0011 .0010 .0009 n, . s. -.0009 .0011 .0010 .0010 n.s. Slope FCM 150-305 days -.1059 .0430 -.0825 .0419 ** -.0956 .0447 .0907 .0419 n. . s. -.0948 .0521 -.0362 .0362 n.s. c n b) Covari ables Trait' FCM 0-50 days (kg) Age (mo.) 2.09701 Milk 0- 50 d.p.p. ( H ) .79563 BWC 0- 60 d.p ( t g ) n.s. FCM 50-100 days (kg) n.s. 58840 n.s. FCM 100-150 days (kg) n.s. 4001 3 n.s. FCM 305 days (kg) n.s. 3. 68808 . n.s. Milk 305 days (kg) n.s. 4. 35779 n.s. Slope milk 0-150 days n.s. - . 00006 .00017 Slope FCM 0-150 days n.s. - . 00007 n.s. Slope milk 150-305 days -.00071 n.s. n.s. Slope fat t 1 50-305 days -.00002 n.s. n.s. Slope FCM 150-305 days -.00077 n.s. n.s. * * n.s. significant (P* .05) significant (P* .01 ) not significant BWC body weight changes, d.p.p. = days post partum 1 No interactions of traits listed in Table 3a were significant. 2 Traits listed in Table 3a without any significant covariables were not listed in Table 3b. T a b l e 4 - M e a n s a n d s t a n d a r d d e v i a t i o n s o f b o d y w e i g h t s a n d b o d y w e i g h t c h a n g e s ( B W C ) i n t h e c u r r e n t l a c t a t i o n a n d a t t h e s u b s e q u e n t c a l v i n g . a ) E a r l y a n d l a t e b r e d g r o u p s , h e a l t h s t a t u s g r o u p a n d g r o u p s a c c o r d i n g t o t h e c a l v i n g s e a s o n a ) b ) I n t e r a c t i o n s a n d c o v a r i a b l e s G r o u p ( G ) H e a l t h s t a t u s ( H ) C a l v i n g s e a s o n ( S ) T r a i t e a r l y b r e d l a t e b r e d n o r m a l a b n o r m a l p a s t u r e n o n - p a s t u r e X n s . d . X n s . d . S i g n . X n s . d . X n s . d . S i g n . x n s . d . X n s . d . S i g n W t . a t c a l v i n g - ( l ) 61 1 4 2 9 7 . 0 6 2 b 4 3 1 0 0 . 7 n . s . 6 3 0 6 0 9 4 . 8 5 8 8 2 5 1 0 2 . 1 n . s . 6 4 8 3 8 9 0 . 7 5 9 5 4 7 9 8 . 9 * BWC 0 - 6 0 d . p . p . - 4 1 4 2 3 7 . 1 - 5 4 4 3 4 0 . 9 n . s . - 5 1 5 9 3 8 . 3 - 3 9 2 5 41 . 4 n . s . - 5 3 3 8 31 . 2 - 4 3 4 7 4 5 . 1 n . s . BWC 0 - 8 0 d . p . p . - 3 1 4 2 4 0 . 1 - 5 0 4 2 41 . 6 n . s . - 4 6 5 9 3 9 . 8 - 2 5 2 4 4 3 . 3 n . s . - 5 6 37 2 6 . 8 - 2 8 4 7 4 7 . 1 ** BWC 6 0 - 8 0 d . p . p . 1 0 4 0 2 3 . 0 6 4 0 2 2 . 5 n . s . 6 5 6 21 . 0 14 24 2 6 . 1 n . s . - 2 3 5 21 . 3 1 6 4 5 2 0 . 7 ** B W C / d a y ( k g / d a y ) : 6 0 d . p . p . t o c a l v i n g - ( 2 ) . 2 8 3 3 . 1 6 . 3 5 3 8 . 1 4 8 0 d . p . p . t o c a l v i n g - ( 2 ) . 2 7 3 3 . 1 7 . 3 5 3 8 . 1 6 W t . a t c a l v i n g - ( 2 ) 6 5 7 31 6 0 . 9 6 8 9 3 8 5 9 . 0 BWC c a l v i n g - ( l ) t o c a l v i n g - ( 2 ) 4 5 31 6 6 . 5 6 7 37 7 0 . 2 W t . o f c a l f ( 1 ) 4 2 . 0 3 3 4 . 9 4 3 . 2 3 6 5 . 8 . 3 0 4 9 . 3 0 * 6 7 4 4 4 n . s . 4 2 . 1 4 9 4 8 4 7 4 7 . 1 4 . 1 5 6 0 . 8 6 0 . 5 4 . 9 . 3 5 2 2 . 3 3 6 7 4 8 6 4 3 . 8 2 2 21 21 2 2 . 1 8 . 1 8 6 4 . 9 7 8 . 5 5 . 9 n . s . n . s . n . s . . 2 5 . 2 6 6 8 3 2 6 4 4 3 3 33 32 31 31 . 14 . 1 6 5 5 . 8 61 . 2 5 . 8 . 3 7 . 3 4 6 6 7 8 0 41 3 8 3 8 3 7 3 7 3 8 . 1 5 • 17 6 6 . 2 6 5 . 8 4 . 6 n . s . n . s . b) T r a i t I n t e r a c t i o n s W t . a t c a l v i n g - ( l ) G x H n . s . G x S n . s . H x S n . s . G x H x S n . s . 3 A g e ( m o . ) . 6 4 8 1 9 BWC 0 - 8 0 d . p . p . n . s . n . s . n . s . n . s . n . s . BWC 6 0 - 8 0 d . p . p . n . s . n . s . n . s . n . s . n . s . 6 0 d . p . p . - c a l v i n g - ( 2 ) n . s . n . s . n . s . n . s . - . 0 0 9 9 8 8 0 d . p . p . - c a 1 v i n g - ( 2 ) n . s . n . s . n . s . n . s . 0 . 0 1 0 0 1 W t . a t c a l v i n g - ( 2 ) n . s . n . s . n . s . n . s . n . s . BWC c a l v i n g - t i ) t o c a l v i n g - ( 2 ) n . s . n . s . n . s . n . s . - 3 . 5 9 6 4 1 W t . o f c a l f ( 1 ) n . s . * n . s . n . s . n . s . C o v a r i a b l e s M i l k 0 - 5 0 d . p . p . u « > . 2 4 9 1 6 n . . s . n . s . n . s . . 2 6 6 8 8 . 0 4 0 5 7 n . s . BWC 0 - 6 0 d . p . p - . 5 3 8 6 3 . 7 0 9 7 6 - . 2 8 2 1 5 n . s . n . s . n . s . . 7 9 2 0 7 . 0 1 1 4 0 * * n . s . BWC s i g n i f i c a n t ( P & . 0 5 ) s i g n i f i c a n t ( P f e . O l ) n o t s i g n i f i c a n t b o d y w e i g h t c h a n g e s , d . p . p . = d a y s p o s t p a r t u m 1 T r a i t s l i s t e d i n T a b l e 4 a w i t h o u t a n y s i g n i f i c a n t i n t e r a c t i o n s a n d c o v a r i a b l e s w e r e n o t l i s t e d i n T a b l e 4 b . Table 5: Means and standard deviations for traits in the subsequent lactation. a) Early and late bred groups, health status group and groups according to the calving season b) Interactions and covariables a) Groups (G) Health status (H) Calving season (S) Trait early bred late bred normal abnormal Pasture Non -Pasture x s.d. X s.d. Si gn. X s.d. X s.d. Sign. X s.d. X s.d. Sign Calving weight (kg) 657 97.0 689 100.7 * 675 60.8 675 64.9 n.s. 683 55.8 667 64.4 n. s. Weight of calf (kg) 47 5.3 45 5.8 n. s . 45 7.2 48 6.4 * 47 8.3 46 6.0 n. s. BWC 0-60 d.p.p. (kg) -55 33.0 -66 39.4 n. s. -56 33.1 -71 42.6 n.s. -55 31.8 -64 40.5 n. s. BWC 0-80 d.p.p. (kg) -32 45.9 -54 43.9 n. s. -36 47.5 -63 35.2 n.s. -40 45.7 -49 47.0 n. s. BWC 60-80 d.p.p.(kg) 18 22.5 8 27,9 n. s . 20 26.3 8 22.2 n.s. 13 23.1 14 30.1 n. s. M1lk 0-50 days (kg) 1620 409 1803 250 n. s. 1701 360 1739 322 n.s. 1756 290 1672 385 n. s. Fat t 0-50 days 3.73 .64 3.80 .48 n. s. 3.84 .56 3.62 .54 * 3.69 .63 3.84 .47 * FCM 0-50 days (kg) 1540 40.6 1745 253 n. s . 1648 367 1636 315 n.s. 1663 260 1624 410 n. s. Slope milk 0-50 days 1444 .1701 . 1702 .1702 n. s. .1399 1771 .1945 .1472 n.s. 2125 .1108 .1115 .1921 ** Slope fat 0-50 days -. 0059 .0113 0069 .0069 n. s. -.0064 0125 - .0063 .0106 n.s. 0090 .0136 .0042 .0100 n. s. Slope FCM 0-50 days 1170 .1589 • 1376 .1376 n. s. .1111 1720 .1617 .1316 n.s. 1679 .1187 .0939 .1813 * Slope milk 0-150 da. -. 0640 .0353 -. 0318 .0361 ** -.0467 ,0317 - .0522 .0421 n.s. 0508 .0364 -.0468 .0404 n. s. Slope fat I 0-150 da. -. 0025 .0055 -. 0036 .0054 n. s. -.0026 0048 - .0039 .0067 n.s. 0026 .0057 -.0032 .0053 n. s. Slope FCM 0-150 days b) Trait 1 Calving weight (kg) -. ,0709 .0302 0492 .0390 * -.0570 0373 .0672 .0338 n.s. 0585 .0342 -.0607 .0378 n. s. G x H n.s. Interactions G x S S x H n.s. n.s. G x 1 n H x S . s. Age (mo. ) n.s. Covariables Milk 0-50 BWC d.p.p.(n) d. .26688 n. 0-60 , p . p .(»»> , s. • BWC 0-60 d.p.p. (kg) n .s. n.s. n.s. n . s. 2.22134 -.10406 n. . s. BWC 0-80 d.p.p. (kg) M1lk 0-50 days (kg) * n.s. n.s. n.s. n.s. n.s. n n . s. . s. n. n. s. s. -.12510 .60117 n, n, . s. . s. * ** n.s. significant (P* significant (P* not significant .05) .01) FCM 0-50 days (kg) n . s. n.s. n.s. n . s. n. s. .42136 n, . s. BWC = body weight changes, d. p.p. = days post partum Slope milk 0-50 days n . s. n.s. n.s. n . s. n. s . -.00018 - .00072 Slope FCM 0-50 days Slope milk 0-150 da. Slope FCM 0-150 days n n n . s. . s. . s. n.s. n.s. n.s. n.s. n.s. n.s. n n n . s. . s. . s. n. n. n. s. s. s . -.00019 -.00005 -.00005 .00067 n.s. n.s. 1 Traits listed i nteracti ons Table 5b. in Table 5a without any and covariables were not significant listed In - 98 - T a b l e 6: C o r r e l a t i o n s b e t w e e n b o d y w e i g h t a n d b o d y w e i g h t c h a n g e s (BWC) i n t h e c u r r e n t l a c t a t i o n . C a l v i n g W e i g h t BWC BWC BWC BWC T r a i t w e i g h t o f 0-60 0-80 6 0 - 8 0 c a l v . ( l ) - ( 1 ) c a l f ( l ) d pp d p p dpp c a l v . ( 2 ) C a l v i n g w e i g h t ( 1 ) 1.00 W e i g h t o f c a l f ( 1 ) . 3 3 * * 1.00 BWC 0-60 d . p . p . - . 6 3 * * -.18 1.00 BWC 0-80 d . p . p . - . 6 5 * * - . 2 3 . 8 4 * * 1.00 BWC 6 0 - 8 0 d . p . p . - . 1 3 -.14 -.17 . 3 7 * * 1.00 BWC c a l v i n g ( 1 ) - c a l v i n g ( 2 ) - . 7 8 * * -.09 . 6 7 * * . 6 7 * * .10 1.00 C a l v i n g w e i g h t ( 2 ) . 7 2 * * . 7 2 * * - . 2 7 * - . 2 9 * -.08 - . 1 0 ( 1 ) = c u r r e n t l a c t a t i o n ( 2 ) = s u b s e q u e n t l a c t a t i o n S i g n i f i c a n t c o r r e l a t i o n s * P 6 . 0 5 , ** P & .01 d . p . p . = d a y s p o s t p a r t u m T a b l e 7: C o r r e l a t i o n s b e t w e e n b o d y w e i g h t a n d b o d y w e i g h t c h a n g e s (BWC) i n t h e s u b s e q u e n t l a c t a t i o n . T r a i t BWC c a l v . (1 ) - c a l v . ( 2 ) C a l v i n g w e i gh t ( 2 ) W e i g h t o f c a l f ( 2 ) BWC 0-60 d p p ( 2 ) BWC 0-80 d p p ( 2 ) BWC c a l v i n g (1 ) - c a l v i n g ( 2 ) 1 .00 C a l v i n g w e i g h t ( 2 ) -.10 1 .00 W e i g h t o f c a l f ( 2 ) -.06 . 3 3 * * 1 .00 BWC 0-60 d . p . p . ( 2 ) - . 2 5 - . 1 9 .11 1 .00 BWC 0-80 d . p . p . ( 2 ) - . 2 5 -.17 .03 . 7 6 * * 1 .00 BWC 6 0 - 8 0 d . p . p . ( 2 ) -.17 .00 .10 -.02 . 4 5 * * ( 1 ) = c u r r e n t l a c t a t i o n , ( 2 ) = s u b s e q u e n t l a c t a t i o n * * S i g n i f i c a n t c o r r e l a t i o n : P ^ .01 d . p . p . = d a y s p o s t p a r t u m - 99 - T a b l e 8 : C o r r e l a t i o n s b e t w e e n b o d y w e i g h t s a n d b o d y w e i g h t c h a n g e s ( B W C ) a n d m i l k p r o d u c t i o n i n t h e c u r r e n t l a c t a t i o n . C a l v i n g B W C B W C B W C T r a i t w e i g h t 0 - 6 0 0 - 8 0 c a l v i n g ( 1 ) d p p d p p c a l v i n g F C M 0 - 5 0 d a y s . 8 3 * * - . 6 6 * * - . 6 6 * * - . 6 4 * * F C M 5 0 - 1 0 0 d a y s . 4 4 * * - . 2 9 * - . 3 0 * - . 5 6 * * F C M 1 0 0 - 1 5 0 d a y s . 6 5 * * - . 4 5 * * - . 4 5 * * - . 5 1 * * F C M 3 0 5 d a y s . 5 8 * * - . 4 5 * * - . 4 5 * * - . 5 0 * * F a t % 3 0 5 d a y s . 0 3 - . 0 8 - . 0 6 - . 0 5 M i l k 3 0 5 d a y s . 5 6 * * - . 4 2 * * - . 4 3 * * - . 4 6 * * S l o p e F C M 0 - 1 5 0 - . 4 5 * * . 4 6 * * . 4 8 * * • . 4 1 * * S l o p e F C M 1 5 0 - 3 0 5 . 0 1 - . 2 6 . 0 0 . 2 9 * S l o p e F C M 0 - 3 0 5 . 3 4 * * - . 5 4 * * . 3 6 * * . 4 7 * * ( 1 ) = c u r r e n t l a c t a t i o n , ( 2 ) = s u b s e q u e n t l a c t a t i o n S i g n i f i c a n t c o r r e l a t i o n s : * P A . 0 5 , * * P . 0 1 d . p . p . = d a y s p o s t p a r t u m T a b l e 9 : C o r r e l a t i o n s b e t w e e n b o d y w e i g h t a n d b o d y w e i g h t c h a n g e s ( B W C ) a n d m i l k p r o d u c t i o n i n t h e s u b s e q u e n t l a c t a t i o n . T r a i t B W C c a l v . ( 1 ) - c a l v . ( 2 ) C a l v i n g w e i g h t ( 2 ) B W C 0 - 6 0 d p p ( 2 ) B W C 0 - 8 0 d p p ( 2 ) F C M 0 - 5 0 d a y s - . 1 0 . 1 3 - . 0 6 - . 1 6 F C M 5 0 - 1 0 0 d a y s - . 0 1 . 4 0 * * - . 2 3 - . 3 2 * F C M 1 0 0 - 1 5 0 d a y s - . 3 0 * . 3 7 * * - . 0 0 - . 0 7 F a t % 0 - 1 5 0 d a y s . 0 9 - . 1 9 . 0 5 . 1 7 S l o p e M i l k 0 - 1 5 0 d a y s - . 2 3 - . 0 7 - . 0 3 . 0 4 S l o p e F a t % 0 - 1 5 0 d a . . 1 6 . 0 0 . 2 4 . 1 3 S l o p e F C M 0 - 1 5 0 d a y s - . 1 2 - . 1 0 . 2 1 . 2 0 ( 1 ) = c u r r e n t l a c t a t i o n , ( 2 ) = s u b s e q u e n t l a c t a t i o n S i g n i f i c a n t c o r r e l a t i o n s : * P & . 0 5 , * * P 4 . 0 1 d . p . p . = d a y s p o s t p a r t u m

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