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Analyses of the yield of milk, milk component, and energy in a Holstein, Ayrshire and Holstein-Ayrshire.. 1971

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ANALYSES OF THE YIELD OF MILK, MILK COMPONENT, AND ENERGY IN A HOLSTEIN, AYRSHIRE AND HOLSTEIN-AYRSHIRE CROSS DAIRY CATTLE POPULATION BY CHRISTOPHER JOHN WILLIAMS B.S.A. U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department o f A n i m a l S c i e n c e a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May, 1971 . In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and S t udy . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rpo se s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s thes. i s f o r f i n a n c i a l g a i n s h a l l no t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Animal Science The U n i v e r s i t y o f B r i t i s h Co lumb ia Vancouve r 8, Canada Date May 3 1971 - i - ABSTRACT A t o t a l o f 238 r e c o r d s (IQ1 H o l s t e i n , 63 A y r s h i r e and m c r o s s b r e d ) made by cows c a l v i n g i n a two ye a r p e r i o d from August 1967 t o J u l y 1969 i n c l u s i v e at the Oy s t e r R i v e r Research Farm were used t o study: a) l a c t a t i o n y i e l d s o f ; m i l k , milk f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s , and energy; b) l a c t a t i o n average p e r c e n t ; milk f a t , p r o t e i n l a c t o s e and t o t a l o r g a n i c s o l i d s ; c) p e r c e n t milk energy as; milk f a t , p r o t e i n and l a c t o s e ; d) the r a t i o o f f a t p r o d u c t i o n to p r o t e i n p r o d u c t i o n , and e) the energy c o n c e n t r a t i o n o f the m i l k . S t a t i s t i c a l a n a l y s e s were by the l e a s t squares method o f Harvey (16). Constants were f i t t e d f o r the t h r e e breed groups, f o r the two years i n c l u d e d i n t h i s study and f o r the season o f l a c t a t i o n s t a r t . Constants were a l s o f i t t e d f o r a l l i n t e r a c t i o n s . Number of days m i l k e d , age i n days o f the cow at p a r t u r i t i o n , and number o f days open were used as c o - v a r i a b l e s . A s i g n i f i c a n c e l e v e l o f 5 p e r c e n t was used throughout. Breed group and the c o - v a r i a b l e s o f days m i l k e d and age were s i g n i f i c a n t f o r y i e l d t r a i t s . The H o l s t e i n s and c r o s s b r e d s d i d not d i f f e r s i g n i f i c a n t l y from each o t h e r but both groups had s i g n i f i c a n t l y h i g h e r y i e l d s than the A y r s h i r e s . The l e a s t squares o v e r a l l means f o r y i e l d s o f ; m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s and energy were; 14,914 + 177, 548 + 7 . 3 , 510.9 + 6 . 1 , 738.4 + 9 . 2 , 1,797.6 + 21.2 l b s . , and 4,946 + 58.9 meal r e s p e c t i v e l y . The l e a s t s qua re s c o n s t a n t s f o r each b r e e d f o r t h e above l i s t e d t r a i t s ( i n t h e same o r d e r ) we re : 1) H o l s t e i n ; 1,239 + 244, 14.2 + 1 0 . 0 , 27.2 + 8.4 60.2 + 12.7 l b s . , and 238.6 + 81.2 m e a l ; 2) c r o s s b r e d 688 + 240, 21.6 + 9 . 9 , 26.2 + 8 .2 , 37.2 + 12.5 l b s . , and 225.6 + 80.1 m e a l s ; and 3) A y r s h i r e ; -1927 + 256, - 35 .8 + 1 0 . 5 , - 53 .4 + 8 .8 , -97 + 1 3 . 3 , - 186 .5 + 30.7 l b s . , and -464 + 85.1 m e a l s . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s o f a l l y i e l d t r a i t s on number o f days m i l k e d and on age a t p a r t u r i t i o n were s i g n i f i c a n t and p o s i t i v e . The o v e r a l l l e a s t s qua re s mean p e r c e n t p r o t e i n was 3.44 + 0 .015 . The b r e e d l e a s t s qua re s c o n s t a n t s f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e w e r e ; - 0 .11 + 0 . 0 2 1 , ).02 + 0 . 0 2 1 , and 0.09 + 0.022 r e s p e c t i v e l y . D i f f e r e n c e s between c r o s s b r e d and A y r s h i r e means were non s i g n i f i c a n t bu t b o t h b r e e d group means were s i g n i f i c a n t l y h i g h e r t h a n t he H o l s t e i n . B r e e d , s e a s o n , b r e e d by sea son and y e a r by s ea son were s i g n i f i c a n t s o u r c e s o f v a r i a t i o n f o r p e r c e n t m i l k f a t and p e r c e n t t o t a l o r g a n i c s o l i d s . A y r s h i r e means were h i g h e r t h a n H o l s t e i n f o r a l l s e a s o n s . F o r w i n t e r c a l v i n g , c r o s s b r e d means d i d no t d i f f e r s i g n i f i c a n t l y f r om H o l s t e i n ; f o r summer c a l v i n g , c r o s s b r e d means d i d no t d i f f e r s i g n i f i c a n t l y f rom A y r s h i r e . D i f f e r e n c e s among H o l s t e i n sea son means were non s i g n i f i c a n t . C r o s s b r e d s and A y r s h i r e s c a l v i n g i n t h e summer tended t o have h i g h e r percentages than w i n t e r o r s p r i n g c a l v e r s . Means o f w i n t e r c a l v i n g cows were h i g h e r i n the second y e a r than i n the f i r s t y e a r . Percent l a c t o s e i n c r e a s e d from 4.88 + 0.019 i n the f i r s t y e a r t o 5.02 + 0.017 i n the second y e a r . S i g n i f i c a n t s t a n d a r d p a r t i a l r e g r e s s i o n c o e f f i c i e n t s f o r days m i l k e d were; p e r c e n t m i l k f a t 0.2 7 + 0.06, p e r c e n t l a c t o s e 0.2 8 + 0.06, and p e r c e n t t o t a l o r g a n i c 0.31 + 0.06. Breed, season, breed by season, y e a r by season and days mi l k e d were a l l s i g n i f i c a n t e f f e c t s on p e r c e n t m i l k energy as milk f a t , the r a t i o o f milk f a t to p r o t e i n and the energy c o n c e n t r a t i o n o f the m i l k . Since p e r c e n t m i l k f a t i s h i g h l y c o r r e l a t e d w i t h the above t r a i t s ( c o r r e l a t i o n c o e f f i c i e n t s were 0.96, 0.86, and 0.97 r e s p e c t i v e l y ) the r e s u l t s were very s i m i l a r t o those o b t a i n e d f o r p e r c e n t m i l k f a t . Season, year , breed by season and days m i l k e d were s i g n i f i c a n t e f f e c t s on p e r c e n t m i l k energy as p r o t e i n . Higher values were a s s o c i a t e d w i t h w i n t e r c a l v i n g than summer c a l v i n g and the e f f e c t o f season was g r e a t e r on c r o s s b r e d than on the o t h e r two breed groups. The st a n d a r d p a r t i a l r e g r e s s i o n c o e f f i c i e n t f o r days m i l k e d was -0.2 8 + 0.07. The means f o r the f i r s t y ear was 27.8 + 0.20 and f o r the second was 2 7 . 2 + 0 . 2 5 . Breed, season, year by season and age were s i g n i f i c a n t f o r p e r c e n t energy as l a c t o s e . Breed means, which were a l l s i g n i f i c a n t l y d i f f e r e n t from each o t h e r were 27.7 + 0.22, 26.8 + 0.20 and 25.6 + 0.24 f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e r e s p e c t i v e l y . Higher values were a s s o c i a t e d with w i n t e r c a l v i n g and d i f f e r e n c e s were g r e a t e r i n the f i r s t y e a r than the second y e a r . The standar d p a r t i a l r e g r e s s i o n c o e f f i c i e n t f o r age was -.20 + 0.06. - V - ACKNOWLEDGMENTS The author wishes t o thank Dr. J.C. Be r r y , under whose d i r e c t i o n t h i s study was i n i t i a t e d , and Dr. R.G. Pet e r s o n , under whose s u p e r v i s i o n t h i s study was completed, f o r t h e i r a s s i s t a n c e i n p l a n n i n g the p r o j e c t and i n a n a l y s i n g the r e s u l t s . The author a l s o thanks Dr. C.W. Roberts f o r h i s s u g g e s t i o n s and c r i t i c i s m s . Thanks are a l s o extended t o Mr. Leo Kansky, Manager o f U.B.C. Research Farm a t Oyster R i v e r , f o r c o l l e c t i o n o f the milk samples and t o Mr. T. Chao f o r analyses o f the samples. The author a l s o wishes t o express h i s s i n c e r e thanks to h i s w i f e f o r her support and encouragement. - v i - TABLE OF CONTENTS PAGE INTRODUCTION 1 LITERATURE REVIEW 3 E f f e c t o f Season on Pe r f o rmance 3 E f f e c t o f Age o f t h e Cow on P e r f o r m a n c e 5 P h e n o t y p i c C o r r e l a t i o n s between P e r f o r m a n c e T r a i t s 5 C r o s s - b r e e d i n g D a i r y C a t t l e 6 MATERIALS AND METHODS 8 Sou rce o f d a t a 8 C o l l e c t i o n and A n a l y s e s o f t h e Samples 9 P e r f o r m a n c e T r a i t s S t u d i e d 11 S t a t i s t i c a l Methods 12 LACTATION Y IELDS: RESULTS AND DISCUSSION 19 B reed Group 19 Season o f C a l v i n g 2 6 Y e a r 26 C o - v a r i a b l e s 2 6 Summary o f Y i e l d T r a i t s 32 MILK COMPOSITION: RESULTS AND DISCUSSION 3 3 B reed Group 3 3 Season o f C a l v i n g 37 Y e a r 39 B reed by Season I n t e r a c t i o n 40 Y e a r by Season I n t e r a c t i o n 47 Days M i l k e d and Age a t P a r t u r i t i o n 5 3 Summary o f M i l k C o m p o s i t i o n 56 ENERGY RELATIONSHIPS: RESULTS AND DISCUSSION 58 B reed Group ' 5 8 Season o f C a l v i n g 62 Y e a r 6 3 B reed by Season I n t e r a c t i o n 6 3 Y e a r by Season I n t e r a c t i o n 71 Days M i l k e d and Age a t P a r t u r i t i o n 8 3 Summary o f Ene rgy R e l a t i o n s h i p s 84 CORRELATIONS BETWEEN PERFORMANCE TRAITS 86 CONCLUSIONS AND SUMMARY 89 LITERATURE CITED 9 3 - v i i - LIST OF FIGURES FIGURE PAGE 1 L a c t a t i o n milk and energy- y i e l d s o f the th r e e breed groups 2 2 2 L a c t a t i o n y i e l d s o f ; milk f a t , p r o t e i n and l a c t o s e o f the th r e e breed groups 2 3 3 The e f f e c t o f season o f f r e s h e n i n g on l a c t a t i o n y i e l d s o f ; m i l k , milk f a t , p r o t e i n , l a c t o s e and energy ( p l o t t e d i n st a n d a r d measure as d e v i a t i o n s from the mean). 28 4 L a c t a t i o n average pe r c e n t m i l k f a t , p r o t e i n and l a c t o s e f o r the th r e e breed groups 36 5 Breed-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r l a c t a t i o n average per c e n t m i l k f a t 4 3 6 Breed-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r l a c t a t i o n average percent t o t a l o r g a n i c s o l i d s 4 3 7 Year-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r l a c t a t i o n average percent m i l k f a t 49 8 Year-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r l a c t a t i o n average per c e n t t o t a l o r g a n i c s o l i d s 49 9 L a c t a t i o n average percent m i l k energy as; milk f a t , p r o t e i n and l a c t o s e f o r the t h r e e breed groups 61 10 Breed-season l e a s t squares means, as d e v i a t i o n s from the o v e r a l l mean, f o r pe r c e n t milk energy as m i l k f a t 6 7 11 Breed-season l e a s t squares means, as d e v i a t i o n s from the o v e r a l l mean, f o r pe r c e n t milk energy as p r o t e i n 6 7 12 Breed-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r the r a t i o o f mi l k f a t t o p r o t e i n 7 3 13 Breed-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r the energy c o n c e n t r a t i o n o f the milk ( k i l o c a l o r i e s p e r pound) 7 3 - V l l l - Year-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r p e r c e n t milk energy as milk f a t Year-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r percent milk energy as l a c t o s e Year-season s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean, f o r the r a t i o o f mi l k f a t t o p r o t e i n Year-season s u b c l a s s means, from the o v e r a l l mean, f o r c o n c e n t r a t i o n o f the milk as the d e v i a t i o n s energy - i x - L IST OF TABLES TABLE PAGE 1 Number o f r e c o r d s c l a s s i f i e d by b r e e d , y e a r and s ea son 9 2 Dates o f m i l k s a m p l i n g 10 3 A r i t h m e t i c means o f t h e c o - v a r i a b l e s 14 4 Number o f cows and number o f r e c o r d s by b r e e d and age a t p a r t u r i t i o n 18 5 Summary o f t he a n a l y s e s o f v a r i a n c e : L a c t a t i o n y i e l d s 20 6 O v e r a l l means and b r e e d g roup l e a s t s qua re s c o n s t a n t s : l a c t a t i o n y i e l d s 21 7 Season l e a s t s qua re s c o n s t a n t s : L a c t a t i o n y i e l d s 2 7 8 Y e a r l e a s t s qua re s c o n s t a n t s : L a c t a t i o n y i e l d s 29 9 P a r t i a l and s t a n d a r d p a r t i a l r e g r e s s i o n c o e f f i c i e n t s : l a c t a t i o n y i e l d s on days m i l k e d and age a t p a r t u r i t i o n 30 10 Summary o f t h e a n a l y s i s o f v a r i a n c e : L a c t a t i o n a ve rage m i l k c o m p o s i t i o n 34 11 O v e r a l l means and b r e e d group l e a s t s q u a r e s c o n s t a n t s : l a c t a t i o n a ve rage p e r c e n t m i l k c o m p o s i t i o n 35 12 Season l e a s t s qua re s c o n s t a n t s : l a c t a t i o n ave rage p e r c e n t m i l k c o m p o s i t i o n 3 8 13 Y e a r l e a s t s qua re s c o n s t a n t s : l a c t a t i o n a ve r age p e r c e n t m i l k c o m p o s i t i o n 41 14 B reed by sea son i n t e r a c t i o n l e a s t s qua re s c o n s t a n t s and s u b c l a s s means, as d e v i a t i o n s f r o m the o v e r a l l mean: l a c t a t i o n a ve rage p e r c e n t m i l k f a t 42 15 B reed by sea son i n t e r a c t i o n l e a s t s qua re s c o n s t a n t s and s u b c l a s s means, as d e v i a t i o n s f rom t h e o v e r a l l mean: l a c t a t i o n a ve rage p e r c e n t t o t a l o r g a n i c s o l i d s 46 - X - TABLE 16 Year by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: l a c t a t i o n average pe r c e n t milk f a t 17 Year by season i n t e r a c t i o n l e a s t squares constants and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: l a c t a t i o n average percent t o t a l o r g a n i c s o l i d s 18 P a r t i a l and standar d p a r t i a l r e g r e s s i o n c o e f f i c i e n t : l a c t a t i o n average p e r c e n t composition on days m i l k e d and age at p a r t u r i t i o n 19 Summary o f the analyses o f v a r i a n c e : Energy r e l a t i o n s h i p s 2 0 O v e r a l l means and breed group l e a s t squares c o n s t a n t s : energy r e l a t i o n s h i p s 21 Season l e a s t squares c o n s t a n t s : energy r e l a t i o n s h i p s 22 Year l e a s t squares c o n s t a n t s : energy r e l a t i o n s h i p s 2 3 Breed by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: p e r c e n t energy as mi l k f a t 24 Breed by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: p e r c e n t energy as p r o t e i n 25 Breed by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: r a t i o o f milk f a t to p r o t e i n 26 Breed by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: energy ( k c a l ) per pound o f milk 2 7 Year by season i n t e r a c t i o n l e a s t squares co n s t a n t s and s u b c l a s s means, as d e v i a t i o n s from the o v e r a l l mean: p e r c e n t milk energy as. m i l k f a t - x i - 78 TABLE PAGE 2 8 Y e a r by s e a s o n i n t e r a c t i o n l e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean: p e r c e n t m i l k e n e r g y as l a c t o s e 29 Y e a r by s e a s o n i n t e r a c t i o n l e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean: r a t i o o f m i l k f a t t o p r o t e i n 30 Y e a r by s e a s o n i n t e r a c t i o n l e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean: e n e r g y ( k c a l ) p e r pound o f m i l k 80 82 31 P a r t i a l and s t a n d a r d p a r t i a l r e g r e s s i o n c o e f f i c i e n t s : e n e r g y r e l a t i o n s h i p s on days m i l k e d and age a t p a r t u r i t i o n 8 5 32 P h e n o t y p i c c o r r e l a t i o n s 87 1. INTRODUCTION The emphasis i n animal p r o d u c t i o n today i s on the a b i l i t y o f domestic animals to produce h i g h y i e l d s o f p r o t e i n . Erb (13) suggested t h a t the d a i r y cow o f the f u t u r e s h o u l d produce a maximum amount o f p r o t e i n with a minimum i n p u t o f energy. T h i s c o u l d be achieved by i n c r e a s i n g the output o f p r o t e i n r e l a t i v e t o milk f a t and l a c t o s e as w e l l as by i n c r e a s i n g l a c t a t i o n p r o t e i n y i e l d s . However the p o s i t i v e g e n e t i c c o r r e l a t i o n o f approximately 0.5 (25, 31, 10) between pe r c e n t m i l k f a t and pe r c e n t p r o t e i n would make i n c r e a s i n g p e r c e n t p r o t e i n w h i l e d e c r e a s i n g the percentage o f the major m i l k energy component, milk f a t , a r e l a t i v e l y slow p r o c e s s . With the r a p i d methods o f det e r m i n i n g p r o t e i n content now a v a i l a b l e (7, 11, 20) i t i s p o s s i b l e t o analyse cows and herd m i l k r e g u l a r l y f o r p r o t e i n c o n t e n t . I t has a l s o been shown, LeBaron and Brog (23), t h a t i n p u t o f p r o t e i n i n t o a manufacturing p l a n t can be accounted f o r i n output and t h e r e f o r e t h a t payment f o r m i l k on a p r o t e i n b a s i s i s r e a l i s t i c because d a i r i e s can r e c o v e r the e x t r a c o s t s o f hi g h p r o t e i n milk i n the p r o d u c t s , although t h i s would be d i f f i c u l t f o r f l u i d m i l k s a l e s . Some milk marketing areas are now paying f o r m i l k on p r o t e i n o r s o l i d - n o t - f a t c ontent as w e l l as on milk f a t content (22). Par t o f the m o t i v a t i o n f o r t h i s t h e s i s was the suggestion,• Berry ( 5 ) , t h a t the dairyman's t a r g e t should be 2 . a cow p r o d u c i n g 20,000 pounds o f mil k t e s t i n g 3.0% m i l k f a t and 9.0% s o l i d s - n o t - f a t . Assuming average values f o r ash, and l a c t o s e o f 0.8% and 4.9% r e s p e c t i v e l y , t h i s cow's milk would t e s t 3.3% p r o t e i n and she would produce 29.3% o f h e r t o t a l m i l k energy as p r o t e i n . T h i s t h e s i s i s a study o f the p r o d u c t i o n o f m i l k , energy and the t h r e e major m i l k components o f two breeds o f d a i r y c a t t l e ( H o l s t e i n and A y r s h i r e ) and c r o s s b r e d s from these two breeds i n the U.B.C. Research Herd a t Oyster R i v e r , B.C. In a d d i t i o n the composition o f the m i l k produced (with r e s p e c t to the t h r e e major components) and the r e l a t i o n s h i p between p r o t e i n and energy i n m i l k were c o n s i d e r e d . The l a t t e r t r a i t was s t u d i e d i n o r d e r t o determine i f between breed d i f f e r e n c e s i n m i l k composition and i n the r a t i o o f p e r c e n t m i l k f a t to p e r c e n t p r o t e i n were i n d i c a t i v e o f between breed d i f f e r e n c e s i n p e r c e n t milk energy as p r o t e i n . 3. LITERATURE REVIEW E f f e c t o f Season on Performance V a r i a t i o n i n l a c t a t i o n y i e l d s o f milk are a s s o c i a t e d w i t h the month i n which a cow f r e s h e n s . Wood (39) suggested t h a t , i n the n o r t h e r n hemisphere, lower l a c t a t i o n m i l k y i e l d s are made by summer c a l v i n g cows than by w i n t e r o r s p r i n g c a l v i n g cows. However, he found g r e a t e r s e a s o n a l v a r i a t i o n i n l a c t a t i o n a l m i l k y i e l d s o f cows i n the n o r t h o f B r i t a i n than i n the southwest of B r i t a i n . The h i g h e s t l a c t a t i o n y i e l d s o f milk were made by cows c a l v i n g from October t o December i n both areas. In the U n i t e d S t a t e s of America, Lee e t a l . ( 2 4 ), i n G e o r g i a ; and Blanchard e t a l . (8) i n the Midwest, a l s o found t h a t the h i g h e s t l a c t a t i o n a l m i l k y i e l d s were made by cows c a l v i n g i n the w i n t e r , w h i l e the lowest y i e l d s were made by cows c a l v i n g i n the summer. But Fosgate e t a l . (14) r e p o r t e d t h a t s p r i n g f r e s h e n i n g cows ( G e o r g i a , U.S.A.) produced the most m i l k . Woodward (40), i n the U.S.A., and B a i l e y ( 4 ) , i n England, showed t h a t the h i g h e s t m i l k r e c o r d s were a s s o c i a t e d w i t h autumn c a l v i n g cows. O l o u f a and Jones (29) i n Oregon, found t h a t season of f r e s h e n i n g was a non- s i g n i f i c a n t e f f e c t on l a c t a t i o n a l m i l k p r o d u c t i o n . Gacula et a l . (15) r e p o r t e d breed d i f f e r e n c e s i n the e f f e c t o f season o f c a l v i n g on l a c t a t i o n a l m i l k y i e l d , however he a t t r i b u t e d these apparent breed d i f f e r e n c e s to d i f f e r e n c e s i n herd management. Johnstone e t a l . ( 1 9 ) i n a 4. study o f the e f f e c t o f season of c a l v i n g on l a c t a t i o n y i e l d s o f m i l k over a ten year p e r i o d on J e r s e y s and H o l s t e i n s i n L o u i s i a n n a , found t h a t the J e r s e y breed showed h i g h l y s i g n i f i c a n t d i f f e r e n c e s f o r s e a s o n a l e f f e c t s . The season of c a l v i n g t h a t gave the h i g h e s t milk y i e l d f o r the J e r s e y breed was January t o March and the low was J u l y t o September. However, the H o l s t e i n breed showed o n l y a h i g h l y s i g n i f i c a n t y e a r by season i n t e r a c t i o n . Johnstone a t t r i b u t e d the breed d i f f e r e n c e s t o the H o l s t e i n s b e i n g more s e n s i t i v e t o c l i m a t e changes between years than the J e r s e y s . Thus, i n g e n e r a l , most workers r e p o r t e d t h a t cows c a l v i n g i n the summer were lower i n l a c t a t i o n m i l k p r o d u c t i o n than cows c a l v i n g a t o t h e r times o f the year, but d i f f e r e n c e s were ma n i f e s t as t o which season o f f r e s h e n i n g r e s u l t e d i n the h i g h e s t l a c t a t i o n m i l k y i e l d . In a d d i t i o n t h e r e was some evidence t h a t the response t o season of c a l v i n g v a r i e d both by breed and by year. The e f f e c t o f season o f c a l v i n g on l a c t a t i o n average p e r c e n t f a t was r e p o r t e d (8, 15, 38) t o be t h a t l a t e summer c a l v i n g cows had h i g h e r l a c t a t i o n a l average f a t t e s t s . However,' Sargent e t a l . (34) found no s i g n i f i c a n t e f f e c t o f season of f r e s h e n i n g on p e r c e n t f a t (North C a r o l i n a ) . Waite e t a l . (38) s t u d i e d the e f f e c t o f season on m i l k c o m p o s i t i o n , ( A y r s h i r e c a t t l e i n Scotla n d ) and found t h a t p e r c e n t m i l k f a t was maximum i n October and f e l l t o a low i n June; pe r c e n t p r o t e i n , w h i l e g e n e r a l l y f o l l o w i n g the 5. pattern of percent milk f a t , was high i n May - June and again in September with the lowest values' reached i n the period from January to March. Lactose content was high from January to June, f e l l to a low l e v e l i n August and stayed at a r e l a t i v e l y low l e v e l f o r the remainder of the year. The v a r i a t i o n i n lactose percent was less than that f o r percent protein or milk f a t . E f f e c t of Age of the Cow on Performance Waite e_t a l . (38) showed that increased age of the cow resulted i n higher y i e l d s of milk with lower percentages of components. The e f f e c t on percent lactose due to age was greater than i t was for percent milk fat or protein. The drop i n percent lactose between the f i r s t l a c t a t i o n and grouped ninth and l a t e r l a c t a t i o n s was 0.35, while the drop i n percent milk fat and protein was 0.19 and 0.0 8 res p e c t i v e l y . The f i n d i n g that the e f f e c t of age on the percent composition was small f o r percent milk f a t and protein was supported by i the r e s u l t s of other workers (1, 2, 15, 26). Phenotypic Correlations between Performance T r a i t s Phenotypic co r r e l a t i o n s between y i e l d t r a i t s have been reported: milk y i e l d and milk fat y i e l d , 0.8 3 (37) and 0.88 (8); milk y i e l d and s o l i d s - n o t - f a t y i e l d , 0.97 (37) and 0.9 8 (8); and milk fat y i e l d and s o l i d s - n o t - f a t y i e l d , 0.9 0 (8),.and are high and p o s i t i v e . The phenotypic 6. c o r r e l a t i o n s between p e r c e n t component and l a c t a t i o n a l m i l k y i e l d have a l s o been r e p o r t e d : m i l k y i e l d and p e r c e n t m i l k f a t , - 0 . 21 ( 1 2 ) , - 0 .26 (37) and - 0 . 25 ( 8 ) ; m i l k y i e l d and p e r c e n t s o l i d s - n o t - f a t , - 0 . 16 (8) and - 0 .11 ( 3 7 ) ; and m i l k y i e l d and p e r c e n t t o t a l s o l i d s , - 0 . 24 ( 8 ) ; and a r e g e n e r a l l y l ow and n e g a t i v e . O t h e r p h e n o t y p i c c o r r e l a t i o n s between p e r f o r m a n c e t r a i t s t h a t have been r e p o r t e d a r e : p e r c e n t m i l k f a t and p e r c e n t p r o t e i n 0.45 (4) and 0.4 3 ( 3 2 ) ; and p e r c e n t m i l k f a t and p e r c e n t l a c t o s e , z e r o (8) and s l i g h t l y n e g a t i v e ( 3 2 ) . C r o s s b r e e d i n g o f D a i r y C a t t l e R o b e r t s o n e_t a l . (33) r e v i e w e d t he h i s t o r y o f e x p e r i m e n t a l c r o s s i n g o f d a i r y b r eed s f o r t h e f i r s t h a l f o f t h i s c e n t u r y , and P e a r s o n and McDowe l l (31) r e v i e w e d more r e c e n t r e p o r t s . Johnson e t a l . (18) s t u d i e d two and t h r e e b r e e d c r o s s e s among J e r s e y , H o l s t e i n and Brown Sw i s s c a t t l e and f ound t h a t t h e Brown Sw i s s by J e r s e y c r o s s e s exceeded t h e p r o d u c t i o n o f t h e p a r e n t b r e e d s ; he r e p o r t e d i n c r e a s e s o f 20% i n m i l k y i e l d , 21% m i l k f a t y i e l d and 15% FCM o v e r t h e p a r e n t a l mean. However , he r e p o r t e d t h a t c r o s s e s w i t h H o l s t e i n s e s s e n t i a l l y e q u a l l e d t h e p e r f o r m a n c e o f t h e H o l s t e i n . McDowe l l and M c D a n i e l (27) s t u d i e d H o l s t e i n , A y r s h i r e and Brown Sw i s s w i t h two and t h r e e b r e e d c r o s s e s , 7. found two d i s t i n c t groupings f o r y i e l d s o f m i l k , m i l k f a t , p r o t e i n , SNF, FCM, and energy. T h e ' A y r s h i r e , Brown Swiss, and Swiss by A y r s h i r e c r o s s e s produced l e s s than; the H o l s t e i n , the two breed c r o s s e s t h a t were h a l f H o l s t e i n and the three breed c r o s s b r e d s . The y i e l d s o f the two breed c r o s s e s , i n which H o l s t e i n s were one o f the breeds, exceeded the mean o f the p a r e n t a l breeds. Y i e l d s o f c r o s s b r e d s were not g r e a t e r than H o l s t e i n but l a t e r a n a l y ses (28) showed t h a t i n terms o f income over feed c o s t s c e r t a i n c r o s s e s were more p r o f i t a b l e due to g r e a t e r e f f i c i e n c y o f feed c o n v e r s i o n and b e t t e r m i l k q u a l i t y . There was a l s o an i n d i c a t i o n t h a t f i r s t l a c t a t i o n s u p e r i o r i t y i n the c r o s s b r e d s may not be maintained o v e r t h e i r l i f e t i m e . Both the study o f Brandt e t a l . (9) on Guernsey, H o l s t e i n and Brown Swiss two and th r e e breed c r o s s e s and t h a t o f B e r e s k i n and Touchberry (6) showed no s t a t i s t i c a l l y s i g n i f i c a n t departure from a d d i t i v e g e n e t i c i n h e r i t a n c e . 8. MATERIALS AND METHODS S o u r c e o f D a t a The a n i m a l s i n t h i s s t u d y were f r o m t h e U.B.C. R e s e a r c h H e r d a t O y s t e r R i v e r , B.C. T h i s h e r d o f a p p r o x i - m a t e l y one h u n d r e d and t w e n t y cows o f m i l k i n g age was com- p o s e d o f t h r e e b r e e d g r o u p s ; H o l s t e i n , A y r s h i r e and f i r s t and s e c o n d g e n e r a t i o n c r o s s e s b etween H o l s t e i n and A y r s h i r e . The f i r s t g e n e r a t i o n c r o s s e s were t h e r e s u l t o f m a t i n g H o l s t e i n s i r e s w i t h A y r s h i r e f e m a l e s , r e c i p r o c a l c r o s s e s were a l s o made. The f i r s t g e n e r a t i o n f e m a l e s were mated t o a b u l l o f t h e same b r e e d as t h e i r own dam t o p r o d u c e t h e s e c o n d g e n e r a t i o n c r o s s b r e d s . F o r t h i s s t u d y a l a c t a t i o n r e c o r d was one i n w h i c h a cow h a d m i l k e d more t h a n 180 d a y s . A l l r e c o r d s were t e r m i n a t e d a t 305 d a y s . T h e s e r e c o r d s were made by cows c a l v i n g o v e r a two y e a r p e r i o d ; f r o m A u g u s t 1967 t o J u l y 1969 i n c l u s i v e . A t o t a l o f 238 r e c o r d s were c o m p l e t e d i n t h e h e r d d u r i n g t h i s p e r i o d , and c o n s i s t e d o f ; 101 H o l s t e i n s , 6 3 A y r s h i r e s and 74 c r o s s b r e d . The c r o s s b r e d g r o u p i n c l u d e d b o t h f i r s t and s e c o n d g e n e r a t i o n c r o s s e s and was composed o f - a n i m a l s w h i c h were 50%, 25% and 75% H o l s t e i n . The number o f r e c o r d s made by e a c h o f t h e s e c l a s s e s o f c r o s s b r e d s was 42, 15 and 17 r e s p e c t i v e l y . The d a t a was d i v i d e d on t h e b a s i s o f t h e s e a s o n i n w h i c h l a c t a t i o n s t a r t e d . S i x s e a s o n s were u s e d ; F e b r u a r y - 9 . March, Ap r i l - M a y , J u n e - J u l y , August-September, October- November and December-January. Table 1 l i s t s the number o f re c o r d s by breed, year and season o f f r e s h e n i n g . TABLE 1 NUMBER OF RECORDS CLASSIFIED BY BREED, YEAR AND SEASON Tot 3. JL H o l s t e i n A y r s h i r e Crossbred T o t a l , bv _ y Season v Sea-Year son 67-68 68-69 67-68 68-69 67-68 68-69 67-68 68-69 Feb-Mar 9 7 8 12 5 8 22 27 49 Apr-May 17 20 7 8 10 7 34 35 69 J u n - J u l 10 9 4 4 6 7 20 20 40 Aug-Sep 5 8 1 2 3 2 9 12 21 Oct-Nov 2 4 5 3 7 11 14 18 32 Dec-Jan 4 6 6 3 4 4 14 13 27 TOTAL 47 54 31 32 35 39 113 125 238 C o l l e c t i o n and Analyses o f the Samples M i l k samples f o r analyses were taken by the R.O.P. i n s p e c t o r , a i d e d by the farm s t a f f , at the time o f h i s r e g u l a r v i s i t t o the Oyster R i v e r Herd. The composite m i l k sample c o n s i s t e d o f two ounces of m i l k taken i n the a f t e r n o o n and two ounces taken the f o l l o w i n g morning from the milk o f each cow. The weight o f m i l k from each cow on t e s t day was 10 . re c o r d e d . The dates o f sampling (morning m i l k i n g ) are p r e s e n t e d i n Table 2. TABLE 2 DATES OF MILK SAMPLING Month 1967 1968 1969 1970 January- 29 24 6 February 28 - 11 March - 6 26 A p r i l 8 - 24 May 11 15 - June 16 20 - J u l y 16 23 - August 26 - - September 10 27 9 - October 7 17 - November 16 1 15 - December 19 ' 12 - - M e r c u r i c c h l o r i d e was added t o the samples as a p r e s e r v a t i v e and the samples were shipped by f r e i g h t , i n i n s u l a t e d c o n t a i n e r s w i t h i c e packs, t o the P r o v i n c i a l Govern- ment Branch Laboratory i n Vancouver, B.C. The samples were anal y s e d f o r milk f a t , p r o t e i n and l a c t o s e content u s i n g an i n f r a - r e d m i l k a n a l y s e r (Grubb-Parsons, Mk I I ) . Performance T r a i t s Studied A t o t a l of f i f t e e n performance t r a i t s were studied. These t r a i t s can be divided into three broad groups: 1 ) l a c t a t i o n y i e l d s , 2 ) l a c t a t i o n average percent composition, and 3 ) energy r e l a t i o n s h i p s . Lactational y i e l d s of milk, milk f a t , protein, lactose and t o t a l organic s o l i d s were computed using the i n t e r v a l between test days as the test period. The y i e l d of t o t a l organic s o l i d s was calculated as the sum of the y i e l d s of the three major components of milk; i . e . the milk f a t , protein and lactose ( t o t a l s o l i d y i e l d could not be calculated because no estimate of mineral content of the milk was made). The y i e l d f o r the test period was calculated by multiplying the number of days i n the test period by the arithmetic mean of the performance t r a i t s on the two tes t days. This procedure had the e f f e c t of d i v i d i n g the test period into two equal sub-periods about a centre date, production c r e d i t s f o r the f i r s t sub-period coming from the f i r s t test day informa- t i o n and production c r e d i t s f o r the second sub-period from the second test day information. This method gives a better estimate of l a c t a t i o n a l y i e l d s than does a method that uses a fixed period p a r t i c u l a r l y when the i n t e r v a l between test days v a r i e s , as i s the case i n t h i s study, Sargent et a l . ( 3 < 4 ) . Total energy y i e l d was estimated by multiplying the y i e l d i n pounds o f m i l k f a t , p r o t e i n and l a c t o s e by t h e i r s t a n d a r d v a l u e s , J enne s s and P a t t o n ( 1 7 ) , f o r t h e h e a t s o f c o m b u s t i o n , ( 4 . 1 3 2 , 2.658 and 1.792 m e a l , p e r pound r e s p e c t i v e l y ) and summing t he p r o d u c t s . The l a c t a t i o n a l a ve rage c o m p o s i t i o n o f t h e m i l k was d e t e r m i n e d f o r m i l k f a t , p r o t e i n , l a c t o s e and t o t a l o r g a n i c s o l i d s by d i v i d i n g t h e l a c t a t i o n a l y i e l d o f each component by t h e l a c t a t i o n a l y i e l d o f m i l k , ( e x p r e s s e d as a p e r c e n t a g e ) . The d i s t r i b u t i o n o f t h e ene r gy i n t he m i l k was c a l c u l a t e d by d i v i d i n g t he m e g a c a l o r i e s o f ene rgy i n each component by t h e t o t a l ene rgy y i e l d and e x p r e s s i n g t h e r e s u l t as a p e r c e n t a g e o f t o t a l e n e r g y . A n o t h e r e s t i m a t e o f t h e r e l a t i o n s h i p between ene rgy and p r o t e i n was t h e r a t i o o f m i l k f a t p r o d u c t i o n t o p r o t e i n p r o d u c t i o n . T h i s was c a l c u - l a t e d by d i v i d i n g t h e pounds o f f a t p r oduced by t he pounds o f p r o t e i n ; t h e r e f o r e t h e f i g u r e s r e p o r t e d show t h e w e i g h t o f f a t p r o d u c e d p e r u n i t w e i g h t o f p r o t e i n . S t a t i s t i c a l Methods A l e a s t s qua re s a n a l y s i s a f t e r Harvey (16) was u sed t o e s t i m a t e t he e " e c t s o f b r e e d , y e a r and sea son o f f r e s h e n i n g and a l l i m . a c t i o n s on t h e p e r f o r m a n c e t r a i t s d i s c u s s e d above ; i . e . y i e l d s o f m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s and e n e r g y ; l a c t a t i o n a l a ve rage p e r c e n t m i l k f a t , p r o t e i n , l a c t o s e and t o t a l o r g a n i c 1 3 . s o l i d s ; and the d i s t r i b u t i o n o f t h e ene rgy among t h e t h r e e m a j o r components o f m i l k . Number o f days o p e n , number o f days m i l k e d and age o f t h e cow a t p a r t u r i t i o n were a l l used as c o - v a r i a b l e s t o a d j u s t p e r f o r m a n c e t r a i t s s t u d i e d f o r d i f f e r e n c e s due t o t h e s e f a c t o r s . Days open were d e f i n e d as t h e number o f days between l a c t a t i o n s t a r t and c o n c e p t i o n o r u n t i l t h e end o f t he r e c o r d i f c o n c e p t i o n d i d n o t o c c u r , bu t n o t t o e x ceed 305 d a y s . Days m i l k e d was d e f i n e d as t h e number o f days t h a t t he cow was m i l k e d f r o m t h e f o u r t h day a f t e r c a l v i n g u n t i l c o m p l e t i o n o f t h e l a c t a t i o n , n o t t o e x ceed 30 5 d a y s . Age was t h e age o f t h e cow i n days a t p a r t u r i t i o n , and s i n c e a l l a v a i l a b l e l a c t a t i o n s were i n c l u d e d i n t h i s s t u d y , t h i s c o - v a r i a b l e a d j u s t e d p e r f o r m a n c e t r a i t s f o r t he e f f e c t o f p a r i t y number as w e l l as f o r age a t p a r t u r i t i o n . Records o f p a r i t y g r e a t e r t han one were i n c l u d e d because f i r s t l a c t a t i o n r e c o r d s o f p r o t e i n p r o d u c t i o n were a v a i l a b l e f o r o n l y a s m a l l p r o p o r t i o n o f t h e h e r d ( a n a l y s e s o f m i l k f o r p r o t e i n were n o t s t a r t e d u n t i l September 1967 ) . T h i s c o - v a r i a b l e a l s o a d j u s t e d r e c o r d s f o r t h e a f f e c t s o f s e l e c t i o n , t o t he e x t e n t t h a t i t o c c u r r e d and a c c o u n t e d f o r d i f f e r e n c e s i n p e r f o r m a n c e between age g r o u p s . However , as t h e h e r d s i z e i n c r e a s e d d u r i n g t h i s p e r i o d , s e l e c t i o n on f e m a l e s was r e l a t i v e l y l o w . The a r i t h m e t i c means by b r e e d g r o u p , o f t h e t h r e e c o - v a r i a b l e s a r e r e p o r t e d i n T a b l e 3. TABLE .3 ARITHMETIC MEANS OF THE CO-VARIABLES H o l s t e i n A y r s h i r e C r o s s b r e d s O v e r a l l Days open 141 154 143 145 Days m i l k e d 298 296 299 298 Age - d a y s 1610 1558 1417 1536 - y e a r s (4.41) (4.27) (3.88) (4.21) The l i n e a r m a t h e m a t i c a l model assumed was: y i j k l - a + b. + s. + a k + ( b s ) . . + ( b a ) . k + ( a s ) j k + ( b s a ) i j R g G i j k l + d D i j k l + a A i j k l + e i j k l > w h e r e : y ^ j k - j _ = The o b s e r v e d v a l u e o f t h e v a r i o u s p e r f o r m a n c e t r a i t s u n d e r s t u d y o f t h e 1 t h cow o f t h e i t h b r e e d c a l v i n g i n t h e j * * 1 s e a s o n o f t h e k"1"*1 y e a r , a = The p o p u l a t i o n mean f o r t h e t r a i t u n d e r s t u d y when e q u a l f r e q u e n c i e s e x i s t i n a l l s u b c l a s s e s and G i j k l ' D i j k l a n d A i j k l a 1 1 e ( l u a l z e r o - b i = The e f f e c t o f t h e . i t h b r e e d . "til. S j = The e f f e c t o f t h e j s e a s o n o f f r e s h e n i n g . a k = The e f f e c t o f t h e k y e a r o f f r e s h e n i n g . ( b s ) . . = The j o i n t e f f e c t o f t h e i t h b r e e d i n t h e j t h s e a s o n when t h e e f f e c t s o f b r e e d and s e a s o n a r e h e l d c o n s t a n t 15. ( b a ) . , = The j o i n t e f f e c t o f t h e i t h b r e e d i n t h e k t h i k J y e a r when t h e e f f e c t s o f b r e e d and y e a r a r e h e l d c o n s t a n t . ( s a ) . , = The j o i n t e f f e c t o f t h e j * * 1 s e a s o n i n t h e k**1 3k J y e a r when t h e e f f e c t s o f s e a s o n and y e a r a r e h e l d c o n s t a n t . ( b s a ) . . , = The j o i n t e f f e c t o f t h e i t h b r e e d i n t h e j t h l j k J t h s e a s o n and t h e k y e a r when t h e e f f e c t s o f b r e e d , s e a s o n and y e a r a r e h e l d c o n s t a n t , g = The p a r t i a l r e g r e s s i o n c o e f f i c i e n t o f y ^ ^ - j . o n i j k l . G..,, = The number o f days open a s s o c i a t e d w i t h t h e 1 i j k l i j k l ' i j k l cow o f t h e i ^ * 1 b r e e d f r e s h e n i n g i n t h e j ^ ^ 1 s e a s o n and t h e y e a r . = The p a r t i a l r e g r e s s i o n c o e f f i c i e n t o f y ^ j ^ j . on D. .. . i ] k l . D. , = The number o f days m i l k e d o f t h e l ^ * 1 cow o f t h e i b r e e d f r e s h e n i n g i n t h e j s e a s o n and t h e i t h k y e a r . = The p a r t i a l r e g r e s s i o n c o e f f i c i e n t o f y.- v-, 1 j K l on i ] k l A. ., , = The age i n days a t p a r t u r i t i o n o f t h e 1 cow o f i ] k l & i t h b r e e d f r e s h e n i n g i n t h e j t h s e a s o n and t h e k t h y e a r . e.., , = The random e f f e c t a s s o c i a t e d w i t h t h e 1 cow o f ., . t h , , ^, t h , , t h t h e x b r e e d f r e s h e n i n g i n t h e j s e a s o n and k 16. y e a r , w h i c h i s assumed t o be i n d e p e n d e n t and n o r m a l l y . 2 d i s t r i b u t e d w i t h mean e q u a l z e r o and v a r i a n c e a . A l l e f f e c t s i n t he model e x c e p t were r e g a r d e d as f i x e d . The l e v e l o f s i g n i f i c a n c e was 0 .05 . A i l s i g n i f i c a n t e f f e c t s were t e s t e d by Duncan ' s new m u l t i p l e range t e s t , as m o d i f i e d by Kramer (20) o r by t h e t - t e s t ( 1 6 ) . P h e n o t y p i c c o r r e l a t i o n c o e f f i c i e n t s between a l l p e r f o r m a n c e t r a i t s s t u d i e d were computed. The p r o p o r t i o n o f t he t o t a l sums o f s qua re s t h a t was a c c o u n t e d f o r by f i t t i n g ; t h e s t a t i s t i c a l m o d e l , and each e f f e c t i n t h e mode l were c a l c u l a t e d . D u r i n g t h e p e r i o d c o v e r e d by t h i s s t u d y some cows c o m p l e t e d two l a c t a t i o n s . As no r a t i o n a l b a s i s e x i s t e d f o r u s i n g one o f t h e s e r e c o r d s and d i s c a r d i n g t h e o t h e r , b o t h r e c o r d s were used as i n d e p e n d e n t e s t i m a t e s o f p e r f o r m a n c e t r a i t s . Thus the u n i t o f o b s e r v a t i o n i n t h i s s t u d y was an i n d i v i d u a l l a c t a t i o n r e c o r d r a t h e r t h a n t he p e r f o r m a n c e o f an i n d i v i d u a l cow. Use o f b o t h r e c o r d s i n t h i s way wou ld t e n d t o improve e s t i m a t e s o f y e a r and sea son e f f e c t s . However use o f two r e c o r d s f o r some cows and one r e c o r d f o r o t h e r s wou l d r e s u l t i n g i v i n g t o o much w e i g h t t o t h e p e r f o r m a n c e o f t h e cow w i t h two r e c o r d s as compared t o t h e cow w i t h o n l y one. I f t h e f a c t t h a t a cow had two r e c o r d s was r e l a t e d 17 . t o h e r p e r f o r m a n c e i n t h e f i r s t r e c o r d ; i . e . cows w i t h h i g h p r o d u c t i o n were r e t a i n e d i n t h e h e r d and t h o s e w i t h low p r o d u c t i o n were s o l d , and i f any b r e e d g r o u p h a d more d u p l i c a t e r e c o r d s t h a n a n o t h e r , t h e n b r e e d e s t i m a t e s f o r t h i s b r e e d g r o u p w o u l d t e n d t o be b i a s e d upwards. T a b l e 4 shows t h a t t h e p r o p o r t i o n o f d u p l i c a t e r e c o r d s i s a p p r o x i m a t e l y t h e same f o r e a c h b r e e d g r o u p , and t h a t t h e main r e a s o n f o r cows h a v i n g o n l y one r e c o r d i s t h a t t h e s e cows f r e s h e n e d f o r t h e f i r s t t i m e d u r i n g t h e s e c o n d y e a r o f t h e s t u d y and t h u s h a d t h e o p p o r t u n i t y t o p r o d u c e o n l y one r e c o r d . A n o t h e r r e a s o n f o r a cow h a v i n g o n l y one r e c o r d was t h a t she was r e l a t i v e l y f r e s h when t h e s t u d y s t a r t e d and was n o t i n c l u d e d i n t h e f i r s t y e a r b u t s u b s e - q u e n t l y c o m p l e t e d a r e c o r d i n t h e s e c o n d y e a r . F o r t h e above r e a s o n s i t i s t h e o p i n i o n o f t h e a u t h o r t h a t w h e t h e r a cow h a d one o r two r e c o r d s was m a i n l y a random p r o c e s s and t h e r e f o r e l i t t l e o r no b i a s was i n t r o d u c e d i n b r e e d e s t i m a t e s by u s i n g b o t h l a c t a t i o n r e c o r d s . TABLE 4. NUMBER OF COWS AND NUMBER OF RECORDS BY BREED AND AGE AT PARTURITION AGE HOLSTEIN CROSSBRED AYRSHIRE TOTALS Y r s . #Rec. # S i n g l e a #Rec. # S i n g l e a #Rec. # S i n g I e a #Rec . # S i n g l e a 1 1 - - - - 1 - 2 25 18 20 13 17 9 62 40 3 18 3 22 3 18 3 58 9 4 25 3 21 2 10 2 56 7 5 16 1 5 1 5 - 26 2 6 6 3 5 1 8 4 19 8 7 4 2 1 - 3 -i J . 8 3 8 3 2 - - 1 - 4 2 9 + 3 3 - - 1 - 4 3 T o t a l s 101 35 74 20 63 19 238 74 No. Cows 68 47 41 156 a The number o f cows i n e a c h age g r o u p t h a t c o m p l e t e d o n l y one l a c t a t i o n d u r i n g t h e p e r i o d c o v e r e d by t h i s s t u d y . LACTATION Y IELDS: RESULTS AND DISCUSSION A summary o f t h e r e s u l t s o f t h e a n a l y s e s o f v a r i a n c e o f y i e l d s o f m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s (TOS) and ene rgy i s p r e s e n t e d i n T a b l e 5. T h i s t a b l e 2 shows t h e v a l u e o f R f o r t he s t a t i s t i c a l m o d e l ; i . e . t he p r o p o r t i o n o f t he t o t a l v a r i a t i o n i n each y i e l d t r a i t t h a t was a c c o u n t e d f o r by f i t t i n g : t h e main e f f e c t s o f b r e e d , s ea son and y e a r ; a l l i n t e r a c t i o n s between and among t h e main e f f e c t s ; and t h e t h r e e c o - v a r i a b l e s o f ; days open,, 2 days m i l k e d , and age . The v a l u e o f R f o r each e f f e c t i n t h e mode l ( i . e . t h e p r o p o r t i o n o f t h e t o t a l v a r i a t i o n t h a t was a c c o u n t e d f o r by t h a t e f f e c t ) i s a l s o shown. F o r l a c t a t i o n y i e l d s o f ; m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s , and ene rgy t he s t a t i s t i c a l model a c c o u n t e d f o r ; 60, 5 1 , 58 , 58, 58 , and 57 p e r c e n t r e s p e c t i v e l y o f t he t o t a l v a r i a t i o n . F o r t h e s e t r a i t s t he e f f e c t o f b r e e d g roup and t h e c o - v a r i a b l e s o f ; days m i l k e d , and age a t p a r t u r i t i o n were t h e o n l y c a t e g o r i e s i n the a n a l y s e s o f v a r i a n c e t h a t were s i g n i f i c a n t . B r eed Group The o v e r a l l y i e l d means, w i t h s t a n d a r d e r r o r , and t h e b r e e d group l e a s t s qua re s c o n s t a n t s , w i t h t h e i r s t a n d a r d e r r o r s a r e r e p o r t e d i n T a b l e 6. The l a c t a t i o n p r o d u c t i o n o f m i l k and ene rgy f o r each b r e e d group a r e shown g r a p h i c a l l y i n F i g u r e 1. F i g u r e 2 shows t h e r e l a t i o n s h i p between b r e e d TABLE 5. SUMMARY OF THE ANALYSES OF VARIANCE: LACTATION Y IELDS. Y i e l d T o t a l F i t t e d 1 T o t a l 2 0 • 3 • 3 • Main B r . E f f e c t s 3 Sn. Y r . 3 I n t e r a c t i o n s B r . X S n . B r . X Y r . Y r . X S n . 3' C o - v a r i a b l e s BXSXY Open M i l k e d Age M i l k 0.60 2 . 2 8 x l 0 9 0 .12 * 0.01 - 0.01 0 .01 0.03 - 0 .12 * .14* F a t .51 3 . 1 3 x l 0 6 .0 3* .02 - .03 .02 .02 - .18* .14* P r o t e i n .58 2 . 5 3 x l 0 6 . 0 8 * .02 - .01 .02 .03 - . 1 3 * . 16 * L a c t o s e .58 5 . 8 6 x l 0 6 . 1 1 * .01 - .01 .01 .03 - . 1 3 * . 09 * T o t a l O rg . S o l . . 58 3 . 0 9 x l 0 7 . 08 * .01 - .02 .01 .03 - . 16 * .14* Ene rgy .57 2 . 3 2 x l 0 8 .06 * .01 - .02 - .03 - .17 * . 15 * Deg. o f Freedom 38 237 2 5 1 10 2 5 10 1 1 1 1 F r a c t i o n o f s t a t i s t i c a l t he t o t a l model ( R 2 sums o f ). s qua re s a c c o u n t e d f o r by f i t t i n g t h e e f f e c t s i n t h e 2 T o t a l c o r r e c t e d sums o f s qua re s ( l b s . 2 e x c e p t 2 ene r g y w h i c h xs mea l ) 3 F r a c t i o n o f the t o t a l sums o f model ( v a l u e s l e s s t han 0.01 . s qua re s are n o t a c c o u n t e d f o r shown) . by each e f f e c t i n t h e s t a t i s t i c a l S i g n i f i c a n t s o u r c e o f v a r i a t i o n . TABLE 6 OVERALL MEANS AND BREED GROUP LEAST SQUARES CONSTANTS: LACTATION Y I E L D S 1 O v e r a l l L e a s t S q u a r e s C o n s t a n t s - S.E. Means + S.E. H o l s t e i n C r o s s b r e d A y r s h i r e M i l k 14,914.0 + 177.0 1239. 0 + 2 4 4 . 0 a 688.0 + 240.0 a -1927.0 + 2 5 6 . 0 b F a t 548.2 + 7.3 14.2 + 10. o a 21.6 + 9 . 9 a - 35 . 8 + 10. 5 b P r o t e i n 510.9 + 6.1 27.2 + 8.4 a 2 6.2 + 8 . 2 a - 53.4 + 8.8 b L a c t o s e 738.4 + . 9.2 60. 2 + 12. 7 a 37. 2 + 1 2 . 5 a - 97.4 + 1 3 . 3 b T.O.S. 1,797.6 + 21.2 101.6 + 29. 2 a 84.9 + 2 8 . 9 a - 186.5 + 3 0 . 7 b E n e r g y 4,946.5 + 58.9 238.6 + 8 1 . 2 a 225.6 + 8 0 . l a - 464.2 + 85. l b 1 a,b U n i t s a r e pounds e x c e p t e n e r g y w h i c h i s i n m e g a c a l o r i e s . C o n s t a n t s s u p e r s c r i p t e d by t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t f r o m e a c h o t h e r by Duncan's t e s t . 22. O O O ' CO o o. o in OT £ o w o. CM Q - -J UJ ^ o o" of - I 2 o o O " I D O O O f ro Ls.Sq. -Mean 14,915 w CD 0 0 o> CM <D 1E (0 V. >» < to X3 to O m (0 to o o (0 ro in to" c '5 o MILK o o E CM 0 0 © v. IE k. < o o E CM N m x> Q> k . X3 to to O v- O o o E in CO in c '© to o X ENERGY Ls.Sq •Mean 4,947 cn o o cn O o o m z: m b 2) o o o •< O J - < "8 p ° 5 3 O O o a o ~. . o o o FIGURE 1. L a c t a t i o n m i l k and e n e r g y y i e l d s o f t h e t h r e e b r e e d g r o u p s . 23. O On co O o - Is- o O i CO O o - m o o o - UJ o o - ro O o - CVJ o OH Ls.Sq. Mean 548 10 Xi CO to Xi Is- ro to •o © 1. J Q OT V> o co Xi CO ro m c '© o PROTEIN Ls.Sq. Wean 511. CO CO xz to < to CO Is- Is- •o © J Q in co o t> O Ls.Sq. -Mean 738. CO j Q Oi 0) Is- c '© •4— V) o X LACTOSE FIGURE 2. L a c t a t i o n y i e l d s o f ; m i l k f a t , p r o t e i n and l a c t o s e o f t h e t h r e e b r e e d g r o u p s . groups f o r l a c t a t i o n a l y i e l d s o f m i l k f a t , p r o t e i n and l a c t o s e . Duncan ' s t e s t showed t h a t t h e H o l s t e i n and c r o s s - b r e d g roups d i d no t d i f f e r s i g n i f i c a n t l y i n l a c t a t i o n a l p r o d u c t i o n o f m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s , and ene rgy ( T a b l e 6 ) . However , b o t h b r e e d g roups p r o d u c e d a t a s i g n i f i c a n t l y h i g h e r l e v e l t h a n t h e A y r s h i r e s f o r a l l t h e above t r a i t s . The e f f e c t o f b r e e d a c c o u n t e d f o r 12% o f t h e t o t a l v a r i a t i o n i n l a c t a t i o n m i l k y i e l d . The l e a s t s q u a r e s mean l a c t a t i o n a l m i l k y i e l d s f o r t h e t h r e e b r e e d g roups o f H o l s t e i n , c r o s s b r e d and A y r s h i r e w e r e : 16,153 + 299; 15,603 + 273 ; and 12,988 + 336 pounds r e s p e c t i v e l y . Thus t h e H o l s t e i n s p r o d u c e d 3,166 pounds more m i l k p e r l a c t a t i o n t h a n t he A y r s h i r e s and 551 pounds more t h a n t he c r o s s b r e d s ( n o n - s i g n i f i c a n t ) . The o v e r a l l l e a s t s qua re s mean was 14,914 + 177 pounds . F o r l a c t a t i o n a l y i e l d s o f m i l k f a t t h e e f f e c t o f b r e e d group a c c o u n t e d f o r 3% o f t h e t o t a l v a r i a t i o n . The l a c t a - t i o n p r o d u c t i o n o f m i l k f a t f o r H o l s t e i n s , c r o s s b r e d s and A y r s h i r e s w a s 5 6 2 . 4 + 1 2 . 3 ; 569.8 + 1 1 . 2 ; and 512.4 + 13.8 pounds r e s p e c t i v e l y . The c r o s s b r e d group p r o d u c e d t h e most m i l k f a t p e r l a c t a t i o n . The l a c t a t i o n f a t y i e l d o f t h i s b r e e d group was 7.4 l b s . more t han t h e H o l s t e i n s ( n o n - s i g n i f i c a n t ) and 57.4 l b s . h i g h e r t h a n t h e A y r s h i r e s . The o v e r a l l mean l a c t a - t i o n y i e l d o f m i l k f a t was 548.2 + 7.3 l b s . The e f f e c t o f b r e e d group a c c o u n t e d f o r 8% o f t he t o t a l v a r i a t i o n i n l a c t a t i o n p r o d u c t i o n o f p r o t e i n . The l e a s t s qua re s mean f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e were 538.1 + 1 0 . 2 ; 537.1 + 9 . 4 ; and 458.3 + 11.5 pounds r e s p e c - t i v e l y . The o v e r a l l l e a s t s qua re s mean was 510.9 + 6.1 pounds . The re was a d i f f e r e n c e o f o n l y one pound i n l a c t a - t i o n a l y i e l d o f p r o t e i n between t he H o l s t e i n and c r o s s b r e d b u t t h e s e two groups p r o d u c e d s i g n i f i c a n t l y more p r o t e i n (70 l b s . ) p e r l a c t a t i o n t h a n t h e A y r s h i r e s . F o r l a c t a t i o n a l y i e l d s o f l a c t o s e t h e e f f e c t o f b r e e d group a c c o u n t e d f o r 11% o f t he t o t a l v a r i a t i o n . The l e a s t s qua re s mean f o r t h e t h r e e b r e e d g roups was 79 8.6 + 1 5 . 5 ; 775.6 + 1 4 . 2 ; and 641.1 + 17.5 pounds o f l a c t o s e p e r l a c t a t i o n o f H o l s t e i n , c r o s s b r e d and A y r s h i r e r e s p e c t i v e l y . The o v e r a l l mean was 7 38.4 + 9.2 pounds . The e f f e c t o f b r e e d group a c c o u n t e d f o r 8% o f t h e t o t a l v a r i a t i o n i n l a c t a t i o n y i e l d o f t o t a l o r g a n i c s o l i d s . The y i e l d s o f t o t a l o r g a n i c s o l i d s ( t h e sum o f t h e above y i e l d s o f m i l k f a t , p r o t e i n and l a c t o s e ) f o r t he t h r e e b r e e d g roups were 1899.2 + 3 5 . 9 ; 1882.5 + 3 2 . 8 ; and 1611.1 + 40.3 pounds p e r l a c t a t i o n f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e r e s p e c t i v e l y . The o v e r a l l l e a s t s qua re s mean was 179 7.6 + 21.2 l b s . Thus t h e d i f f e r e n c e ( n o n - s i g n i f i c a n t ) between H o l s t e i n and c r o s s b r e d f o r t o t a l y i e l d o f t h e m a j o r n u t r i e n t s i n m i l k was o n l y 16.7 l b s . , w h i l e t h a t between t h e two p a r e n t a l b r e e d s was 288.1 l b s . i n f a v o u r o f t he H o l s t e i n s . F o r l a c t a t i o n a l y i e l d s o f ene rgy the e f f e c t o f b r e e d g roup a c c o u n t e d f o r 6% o f t he t o t a l v a r i a t i o n . The ene rgy y i e l d s o f t he t h r e e b r e e d g roups were 5185.1 + 9 9 . 5 ; 5172.1 + 9 0 . 9 ; and 4482.7 + 111.8 m e a l , m i l k ene rgy p e r l a c t a t i o n f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e r e s p e c t i v e l y , w i t h an o v e r a l l l e a s t s q u a r e s mean o f 4946.5 + 58.9 m e a l . Season o f C a l v i n g W h i l e t h e e f f e c t o f s ea son o f c a l v i n g on l a c t a t i o n a l y i e l d s d i d n o t a c c o u n t f o r a s i g n i f i c a n t amount o f t h e t o t a l v a r i a t i o n , t h e t r e n d was f o r cows t h a t f r e s h e n e d i n t he autumn and w i n t e r t o p roduce more m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s and ene rgy p e r l a c t a t i o n t h a n t h o s e t h a t f r e s h e n e d i n t he s p r i n g and summer. The l e a s t s q u a r e s c o n s t a n t s and s t a n d a r d e r r o r s f o r s ea son o f f r e s h e n i n g e f f e c t s a r e shown i n T a b l e 7 and a r e g raphed i n F i g u r e 3. Y e a r Y e a r was no t a s i g n i f i c a n t s o u r c e o f v a r i a t i o n o f l a c t a t i o n y i e l d s . The y e a r l e a s t s qua re s c o n s t a n t s w i t h t h e i r s t a n d a r d e r r o r s , f o r l a c t a t i o n y i e l d s a r e shown i n T a b l e 8. C o - v a r i a b l e s ^ The number o f days m i l k e d and t h e age o f t h e cow a t p a r t u r i t i o n were s i g n i f i c a n t e f f e c t s on a l l y i e l d . t r a i t s s t u d i e d . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s a r e r e p o r t e d i n T a b l e 9. The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s a r e t h e p o o l e d w i t h i n s u b c l a s s r e g r e s s i o n s o f y i e l d i n pounds ( o r m e a l , i n t h e ca se o f . e n e r g y y i e l d ) on t he days m i l k e d and on t h e age o f t h e cow, i n d a y s , a t p a r t u r i t i o n . The c o e f f i c i e n t s a r e t h u s TABLE 7. SEASON LEAST SQUARES CONSTANTS: LACTATION YIELDS . 2 L e a s t S q u a r e s C o n s t a n t s - S.E. ^ i e l ^ Feb - Mar A p r - May J u n - J u l Aug - Sep O c t - Nov Dec - J a n M i l k 446.0 + 316.0 - 11.0 + 295.0 -815.0 + 359.0 116.0 + 507.0 -60.0 + 457.0 323.0 + 469.0 F a t - 9.3 + 13.0 - 26.3 + 12.1 - 20.3 + 14.8 43.3 + 20.8 15.1 + 18.8 - 2.5 + 19.2 P r o t e i n 13.8 + 10.8 0.0 + .10.1 - 30.3 + 12.3 17.2 + 17.4 - 5.0 + 15.7 4.3 + 16.1 L a c t o s e 21.3 + 16.4 - 1.4 + 15.3 - 36.3 + 18.7 5.4 + 26.4 - 8.4 + 23.8 19.4 + 24.4 TOS 25.9 + 37.9 - 27.7 + 35.4 - 86.9 + 43.1 65.9 + 60.9 1.7 + 54.8 21.2 + 56.2 E n e r g y 36.6 + 105.2 -111.3 + 98.1 -229.5 + 119.5 234.2 + 170.0 34.0 + 152.2 36.0 + 155.9 1 S e a s o n o f c a l v i n g was n o t a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n y i e l d s . 2 U n i t s a r e p o u n d s , e x c e p t e n e r g y w h i c h i s i n m e g a c a l o r i e s . o —1 • Milk yield o Milk fat yield o Protein yield A Lactose yield FIGURE 3. The e f f e c t o f season o f f r e s h e n i n g on l a c t a t i o n y i e l d s o f ; m i l k , m i l k f a t , p r o t e i n , l a c t o s e and energy ( p l o t t e d i n s t a n d a r d measure as d e v i a t i o n s f r om t h e mean). Season o f f r e s h e n i n g was no t a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r y i e l d t r a i t s . r o C O TABLE 8 YEAR LEAST SQUARES CONSTANTS: LACTATION YIELDS1 Y i e l d 2 1967- 68 + S.E. 1968- 69 + S.E. M i l k -71.5 + 177.6 71.5 + 177.6 F a t - 4.3 + 7.3 4.3 + 7.3 P r o t e i n 1.1 + 6.1 - 1.1 + 6.1 L a c t o s e -13 . 5 + 9.2 13.5 + 9.2 T.O.S. -16 .6 + 21. 3 16 . 6 + 21.3 E n e r g y -38.7 + 59.1 38.7 + 59.1 1 Y e a r was n o t a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n y i e l d s . 2 A l l y i e l d s i n pounds e x c e p t e n e r g y w h i c h i s i n mega c a l o r i e s . TABLE 9 PARTIAL AND STANDARD PARTIAL REGRESSION COEFFICIENTS : LACTATION YIELDS ON DAYS MILKED AND AGE AT PARTURITION DAYS MILKED AGE Y i e l d U n i t s o f Y l d . + S.E. S t a n . . Meas. + S.E. U n i t s 2 o f Y l d . + S.E. S t a n . Meas. + S.E. M i l k 58.8 + 7.7 0. 39 + 0.05 2.12 + 0 . 25 0.43 + 0 .05 F a t 2.74 + 0. 32 .50 + 0.06 0.079 + 0. 010 .43 + 0.06 P r o t e i n 2.08 + 0.26 .42 + 0.05 0.075 + 0. 008 .46 + 0.05 L a c t o s e 3.15 + 0 .40 .42 + 0.05 0.089 + 0. 013 . 35 + 0.05 T.O.S. 7.97 + 0.93 .46 + 0.05 0. 243 + 0 . 030 .42 + 0.05 E n e r g y 22.5 + 2.6 .48 + 0.05 0 .686 + 0. 084 .43 + 0. 05 1 A l l c o e f f i c i e n t s a r e s i g n i f i c a n t 2 U n i t s a r e pounds e x c e p t e n e r g y w h i c h i s i n m e g c . c a l o r i e s t h e i n c r e a s e i n y i e l d p e r day m i l k e d and p e r day o f age above the i n t e r c e p t where days m i l k e d and age b o t h e q u a l z e r o . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s a r e a l s o l i s t e d i n s t a n d a r d measure i n T a b l e 9; t h e s e v a l u e s e s t i m a t e t h e change i n y i e l d , as a f r a c t i o n o f a s t a n d a r d d e v i a t i o n o f y i e l d , a s s o c i a t e d w i t h one s t a n d a r d d e v i a t i o n change i n t h e i n d e p e n - dent v a r i a b l e - - days m i l k e d and age i n days i n t h i s c a s e . The c o - v a r i a b l e o f days m i l k e d a c c o u n t e d f o r 12 , 18 , 1 3 , 1 3 , 16 and 17 p e r c e n t o f t h e t o t a l v a r i a t i o n o f l a c t a t i o n y i e l d s o f m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s and t o t a l ene rgy r e s p e c t i v e l y . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s w e r e : 58.8 + 7.7 (0 .39 + 0 . 0 5 ) ; 2.74 + 0.32 (0 .50 + 0 . 0 6 ) ; 2.08 + 0.26 (0 .42 + 0 . 0 5 ) ; 3.15 + 0.40 (0 .42 + 0 . 0 5 ) ; 7.97 + 0.93 (0 .46 + 0.05) and 22.5 + 2.6 (0 .48 + 0.05) f o r t h e above l i s t e d y i e l d t r a i t s i n t h e same o r d e r . T h e . f i g u r e s i n p a r e n t h e s e s a r e t h e v a l u e s o f t h e p a r t i a l r e g r e s s i o n c o e f f i c i e n t s i n s t a n d a r d measure . The v a l u e s f o r y i e l d o f m i l k f a t and f o r y i e l d o f ene r gy a r e s l i g h t l y h i g h e r t h a n f o r o t h e r y i e l d t r a i t s , t h i s was due t o t h e i n c r e a s e i n f a t p e r c e n t w i t h a d v a n c i n g l a c t a t i o n . The c o - v a r i a b l e o f age a t p a r t u r i t i o n a c c o u n t e d f o r : 14 , 14 , 16 , 9, 14 and 15 p e r c e n t o f t h e t o t a l v a r i a t i o n i n y i e l d s o f m i l k , m i l k f a t , p r o t e i n , l a c t o s e , t o t a l o r g a n i c s o l i d s and e n e r g y r e s p e c t i v e l y . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s ( s t a n d a r d measure i n p a r e n t h e s e s ) f o r t h e above l i s t e d y i e l d t r a i t s w e r e : 2.12 + 0.25 (0 .43 +0 .05 ) ; 0.079 + 0.0 ( 0 .43 + 0 . 0 6 ) ; 0.075 +0.008 (0.46 + 0 . 0 5 ) ; 0.089 + 0.013 (0 .35 + 0 . 0 5 ) ; 0.243 + 0.030 (0.42 + 0 .05) and 0.686 + 0.084 (0 .43 + 0.05) r e s p e c t i v e l y . The r e g r e s s i o n o f y i e l d s on age a r e a l l p o s i t i v e and a r e a p p r o x i m a t e l y t h e same magn i tude f o r a l l y i e l d t r a i t s i n s t a n d a r d measure e x c e p t f o r y i e l d o f l a c t o s e w h i c h was s l i g h t l y l o w e r t h a n t he o t h e r s . T h i s r e s u l t was due t o t h e d rop i n l a c t o s e p e r c e n t i n t h e m i l k o f o l d e r cows . Summary o f Y i e l d T r a i t s I n summary, t h e H o l s t e i n and c r o s s b r e d d i d no t d i f f e r s i g n i f i c a n t l y i n any o f t h e y i e l d t r a i t s s t u d i e d . However , b o t h g roups p r oduced a t a s i g n i f i c a n t l y h i g h e r l e v e l t h a n t he A y r s h i r e s f o r a l l y i e l d t r a i t s . D i f f e r e n c e s i n l a c t a t i o n y i e l d between H o l s t e i n and A y r s h i r e were 3166 l b s . o f m i l k , 288.1 l b s . t o t a l o r g a n i c s o l i d s and 702.8 mea l e n e r g y ; w h i l e t h o s e between c r o s s b r e d and A y r s h i r e we re : 2615 l b s . m i l k , 271.4 l b s . t o t a l o r g a n i c s o l i d s and 689.8 mea l e n e r g y . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s o f a l l y i e l d t r a i t s s t u d i e d on number o f days m i l k e d and on age a t p a r t u r i t i o n were s i g n i f i c a n t and p o s i t i v e . MILK COMPOSITION: RESULTS AND DISCUSSION A summary o f t h e r e s u l t s o f t h e a n a l y s e s o f v a r i a n c e o f l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t , p r o t e i n , l a c t o s e , and t o t a l o r g a n i c s o l i d s i s p r e s e n t e d i n T a b l e 10. F o r t h e above l i s t e d t r a i t s , t h e s t a t i s t i c a l model a c c o u n t e d f o r 43, 28, 39, and 41 p e r c e n t r e s p e c t i v e l y o f t h e t o t a l v a r i a t i o n . The o v e r a l l means, w i t h t h e i r s t a n d a r d e r r o s , and t h e b r e e d g r o u p l e a s t s q u a r e s c o n s t a n t s , w i t h t h e i r s t a n d a r d e r r o s , f o r l a c t a t i o n average, p e r c e n t m i l k f a t , p r o t e i n , l a c t o s e , a n d t o t a l o r g a n i c s o l i d s a r e p r e s e n t e d i n T a b l e I I . B r e e d Group The e f f e c t o f b r e e d g r o u p was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t , p r o t e i n , and t o t a l o r g a n i c s o l i d s b u t n o t f o r l a c t a t i o n a v e r a g e p e r c e n t l a c t o s e ( T a b l e 1 0 ) . B r e e d g r o u p d i f f e r e n c e s i n l a c t a t i o n a v e r a g e p e r c e n t c o m p o s i t i o n a r e shown g r a p h i c a l l y i n F i g u r e 4. B r e e d g r o u p a c c o u n t e d f o r 12% o f t h e t o t a l v a r i a t i o n i n l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t . As t h e i n t e r a c t i o n o f b r e e d by s e a s o n was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r t h i s t r a i t , d i f f e r e n c e s among b r e e d means were r e l a t e d t o t h e s e a s o n i n w h i c h l a c t a t i o n s t a r t e d . The l e a s t s q u a r e s means f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e g r o u p s w e r e : 3.48 + 0.05; 3.68 + 0.04 a n d 3.94 + 0.06 p e r c e n t r e s p e c t i v e l y . Thus t h e c r o s s b r e d g r o u p mean was s l i g h t l y b e l o w t h e o v e r a l l mean o f 3.70 + 0.03 p e r c e n t . TABLE 10. SUMMARY OF THE ANALYSES OF VARIANCE: LACTATION AVERAGE MILK COMPOSITION. T o t a l T o t a l Main E f f e c t s 3 3 I n t e r a c t i o n s 3 C o - v a r i a b l e s Component F i t t e d 1 2 C • S • S • Br. Sn. Yr. Br.XSn. Br.XYr. Yr.XSn. BXSXY Open M i l k e d Age % Fat 0.43 42 .99 .12* .09* - .0 7* .0 7* .03 - 0.0 5* % P r o t e i n .28 9. 31 .10* .02 .01 .03 .03 .06 - - % Lactose .* . 39 7.79 - .09* .04 .02 .02 - .0 6* .11* % TOS .41 78.83 .12* .0 7* - .06* .0 7* .04 - .0 7* Deg. o f Freedom 38 237 2 5 1 10 2 5 10 1 1 1 1 F r a c t i o n o f s t a t i s t i c a l the t o t a l model ( R 2 ) sums o f squares accounted f o r by f i t t i n g the e f f e c t s i n . the 2 T o t a l c o r r e c t e d sums o f squares. 3 F r a c t i o n o f the t o t a l sums o f squares accounted f o r by each e f f e c t i n the s t a t i s t i c a l model (values l e s s than 0.01 are not shown). * S i g n i f i c a n t source o f v a r i a t i o n . CO TABLE 11 OVERALL MEANS AND BREED GROUP LEAST SQUARES CONSTANTS: LACTATION AVERAGE PERCENT MILK COMPOSITION Component O v e r a l l Mean + S.E. L e a s t Squares C o n s t a n t s + S .E. H o l s t e i n C r o s s b r e d A y r s h i r e % F a t * 3. 70 + 0.029 - 0.22 + 0.040 0. 02 + 0.40 0.24 + 0.042 % P r o t e i n 3.44 + .015 - .11 + . 0 2 1 b .02 + . 0 2 1 a .09 + . 0 2 2 a % L a c t o s e 1 1 4.95 + .013 .00 + . .018 .01 + .017 - .01 + .018 % T . O . S . * 12.09 + .040 - .33 + .055 .01 + .054 . 31 + . 058 Breed group was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n b u t Duncan ' s t e s t was not used t o t e s t t he b r e e d means because t h e b r e e d by s ea son i n t e r a c t i o n was a l s o s i g n i f i c a n t . a ,b C o n s t a n t s s u p e r s c r i p t e d by t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t f rom each o t h e r by Duncan ' s t e s t . n . s D i f f e r e n c e s among b r e e d means no t s i g n i f i c a n t by t he a n a l y s i s o f v a r i a n c e 36 . Ls.Sq. -Mean 4.94% o z o t o . o Q. 2 o o _ J CM S to >» < ro 0) i . -O (0 10 o o Ls.Sq. -Mean 3.69% ro c *— to O FAT CM "0 ro m ro -o xt CO (0 o ro ro ro c +- o X PROTEIN Ls.Sq. -Mean 3.43% to CO < to to x--Q (0 to o O If) c a> ••— i2 o x LACTOSE FIGURE 4. L a c t a t i o n a v e r a g e p e r c e n t m i l k f a t , p r o t e i n and l a c t o s e f o r t h e t h r e e b r e e d g r o u p s . F o r l a c t a t i o n a v e r a g e p e r c e n t p r o t e i n , b r e e d g r o u p was t h e o n l y c a t e g o r y i n t h e s t a t i s t i c a l model t h a t was s i g n i f i c a n t . T h i s e f f e c t a c c o u n t e d f o r 10% o f t h e t o t a l v a r i a t i o n ( T a b l e 10) i n p e r c e n t p r o t e i n . Duncan's t e s t showed t h a t t h e c r o s s b r e d and A y r s h i r e b r e e d g r o u p s d i d n o t d i f f e r s i g n i f i c a n t l y i n l a c t a t i o n a v e r a g e p e r c e n t p r o t e i n , b u t b o t h g r o u p s were s i g n i f i c a n t l y h i g h e r f o r t h i s t r a i t t h a n t h e H o l s t e i n s . The l e a s t s q u a r e s means f o r t h e H o l s t e i n , c r o s s - b r e d and A y r s h i r e g r o u p s w e r e : 3.33 + 0.026; 3.46 + 0.02 3; and 3.53 + 0.029 p e r c e n t r e s p e c t i v e l y . The o v e r a l l l e a s t s q u a r e s mean was 3.44 + 0.015 p e r c e n t ( T a b l e 1 1 ) . B r e e d g r o u p a c c o u n t e d f o r 12% o f t h e v a r i a t i o n o f l a c t a t i o n a v e r a g e t o t a l o r g a n i c s o l i d s . The b r e e d s e a s o n i n t e r a c t i o n was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n , as i t was i n t h e c a s e o f p e r c e n t m i l k f a t . The b r e e d g r o u p l e a s t s q u a r e s means f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e w e r e : 11.76 + 0.07, 12.10 + 0.06 and 12.40 + 0.08 p e r c e n t r e s p e c t i v e l y . The o v e r a l l mean was 12.04 + 0.04 p e r c e n t . S e a s o n o f C a l v i n g S e a s o n o f c a l v i n g was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t , and t o t a l o r g a n i c s o l i d s b u t n o t f o r l a c t a t i o n a v e r a g e p e r c e n t p r o t e i n o r l a c t o s e ( T a b l e 1 0 ) . The s e a s o n o f c a l v i n g l e a s t s q u a r e s c o n s t a n t s f o r l a c t a t i o n a v e r a g e m i l k c o m p o s i t i o n a r e r e p o r t e d i n T a b l e 12. S e a s o n o f c a l v i n g a c c o u n t e d f o r 9% o f t h e t o t a l TABLE 1 2 . SEASON LEAST SQUARES CONSTANTS: LACTATION AVERAGE PERCENT MILK COMPOSITION L e a s t Squares C o n s t a n t s + S .E . Component Feb-Mar Apr-May J u n - J u l Aug-Sep Oct -Nov D e c - J a n •% M i l k f a t * - 0 . 1 8 + . 0 5 - 0 . 1 8 + . 0 5 0 . 0 5 + . 0 5 0 . 2 7 + . 0 8 0 . 1 2 + . 0 8 - 0 . 0 8 + . 0 8 % n . . n. s . P r o t e i n - 0 . 0 1 + . 0 3 0 . 0 + . 0 3 - 0 . 0 2 + . 0 3 0 . 1 0 + . 0 4 - 0 . 0 2 + . 0 4 - 0 . 0 5 + . 0 4 % j . n . s. L a c t o s e - 0 . 0 1 + . 0 2 - 0 . 0 1 + . 0 2 0 . 0 2 + . 0 3 0 . 0 + . 0 4 0 . 0 3 + . 0 3 0 . 0 3 + . 0 3 % TOS* - 0 . 2 1 + . 0 7 - 0 . 2 0 + . 0 7 0 . 0 5 + . 0 8 0 . 3 7 + . 1 1 0 . 0 8 + . 1 0 - 0 . 0 9 + . 1 0 Season by c a l v i n g was a s i g n i f i c a n t s ou r ce o f v a r i a t i o n b u t Duncan ' s t e s t was n o t u sed t o t e s t season means because y e a r by sea son and b r e e d by sea son i n t e r a c t i o n s were s i g n i f i c a n t . n . s . D i f f e r e n c e s among season means n o t s i g n i f i c a n t by t h e a n a l y s e s o f v a r i a n c e . v a r i a t i o n o f l a c t a t i o n average p e r c e n t m i l k f a t . Cows c a l v i n g i n the summer and autumn had h i g h e r l a c t a t i o n average p e r c e n t f a t than cows c a l v i n g i n the w i n t e r and s p r i n g . However, the f i r s t o r d e r i n t e r a c t i o n s o f breed by season and y e a r by season were both s i g n i f i c a n t sources o f v a r i a t i o n . T h e r e f o r e the e f f e c t o f season o f c a l v i n g on t h i s t r a i t d i f f e r e d among the t h r e e breed groups and between the two years c o n s i d e r e d i n t h i s study. Season o f f r e s h e n i n g accounted f o r 7% o f the v a r i a t i o n o f l a c t a t i o n average p e r c e n t t o t a l o r g a n i c s o l i d s . The s e a s o n a l a f f e c t was s i m i l a r to t h a t f o r p e r c e n t m i l k f a t and the f i r s t o r d e r i n t e r a c t i o n s o f breed by season and y e a r by season were s i g n i f i c a n t sources o f v a r i a t i o n (as was the case f o r p e r c e n t milk f a t ) . Season o f f r e s h e n i n g was not a s i g n i f i c a n t source o f v a r i a t i o n f o r l a c t a t i o n average p e r c e n t m i l k p r o t e i n . However, the t r e n d was f o r cows c a l v i n g i n August-September t o have the h i g h e s t p e r c e n t p r o t e i n ( t h i s was a l s o the h i g h season f o r p e r c e n t milk f a t ) . The second h i g h e s t season f o r p e r c e n t p r o t e i n was Apr i l - M a y which was the lowest f o r p e r c e n t f a t . T h i s r e s u l t may be i n d i c a t i v e o f a t r e n d f o r s p r i n g g r a z i n g t o i n c r e a s e p e r c e n t p r o t e i n but to lower p e r c e n t m i l k f a t (while i n c r e a s i n g m i l k y i e l d s ) as r e p o r t e d by Waite (38). Year Year l e a s t squares c o n s t a n t s , with t h e i r s t a n d a r d e r r o r s , f o r l a c t a t i o n average m i l k c o m p o s i t i o n are pre s e n t e d 40 . i n Table 13. Year was a s i g n i f i c a n t source o f v a r i a t i o n f o r l a c t a t i o n average p e r c e n t l a c t o s e and accounted f o r 9% of the t o t a l v a r i a t i o n . L a c t a t i o n average p e r c e n t l a c t o s e i n c r e a s e d from 4.88 + 0.019 i n the f i r s t y ear t o 5.02 + 0.017 i n the second year. Year was not a s i g n i f i c a n t source of v a r i a t i o n of l a c t a t i o n average p e r c e n t milk f a t , p r o t e i n o r t o t a l o r g a n i c solids,. Breed by Season I n t e r a c t i o n Breed by season i n t e r a c t i o n was a s i g n i f i c a n t source o f v a r i a t i o n f o r l a c t a t i o n average p e r c e n t milk f a t and t o t a l o r g a n i c s o l i d s , and accounted f o r 7 and 6% r e s p e c t i v e l y o f the t o t a l v a r i a t i o n o f these two t r a i t s . 1 The breed season i n t e r a c t i o n c onstants and the s u b c l a s s means (as d e v i a t i o n s from the o v e r a l l mean) f o r l a c t a t i o n average p e r c e n t milk f a t are shown i n Table 14 and the s u b c l a s s means are graphed i n F i g u r e 5. The s u b c l a s s means (as d e v i a t i o n s from the o v e r a l l mean) were computed by summing the a p p r o p r i a t e c o n s t a n t s f o r the e f f e c t s o f ; breed, season, and breed by season i n t e r a c t i o n . Three o f the breed season i n t e r a c t i o n c o n s t a n t s were s i g n i f i c a n t l y d i f f e r e n t from zero by a t - t e s t (Table 14). These were the constants a s s o c i a t e d w i t h ; 1) H o l s t e i n s c a l v i n g i n A p r i l - M a y , 2) H o l s t e i n s c a l v i n g i n August-September, and 3) c r o s s b r e d s c a l v i n g i n February-March. The i n t e r a c t i o n constants a s s o c i a t e d ; with c r o s s b r e d s c a l v i n g i n December- January and i n August-September and with A y r s h i r e s c a l v i n g TABLE 13 YEAR LEAST SQUARES CONSTANTS: LACTATION AVERAGE PERCENT MILK COMPOSITION Component 1967-68 + S.E. 1968-69 + S .E. % F a t n , S * - 0 . 015 + 0.029 0.015 + 0.029 % P r o t e i n n , S * 0.026 + 0.015 -0 .026 + 0.015 % L a c t o s e * - 0 .068 + 0.013 0.068 + 0.013 % T .O.S . n , S * - 0 . 057 + 0.040 0.057 + 0.040 n . s . D i f f e r e n c e s between y e a r s n o t s i g n i f i c a n t by t he a n a l y s i s o f v a r i a n c e . * D i f f e r e n c e s between y e a r s were s i g n i f i c a n t by t h e a n a l y s i s o f v a r i a n c e . TABLE 14. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: LACTATION AVERAGE PERCENT MILK FAT. A. Least Squares Constant - S.E. B. Subclass means - S.E. Season '- ^—^ H o l s t e i n Crossbred A y r s h i r e H o l s t e i n ' ' Crossbred A y r s h i r e Feb - Mar .07 + .07 -.17 + .0 7* .10 + .07 - .33 + .09 • -.37 + .10 b .15 + .0 8 a b Apr - May .16 + .0 6* -.08 + .07 -.08 + .07 -.2 5 + .06 -.2 8 + .08 b -.02 + .09 b Jun - J u l .01 + .07 .12 + .08 -.13 + .08 -.17 + .09 .13 + .10 a .17 + . 1 2 a b Aug - Sep -.22 + .10* .19 + .12 . .03 + .14 -.17 + .10 .44 + .15 a .55 + .20 a Oct - Nov .00 + .12 .13 + .09 -.13 + .10 -.10 + .19 .24 + .12 a .23 + . 1 3 a b Dec - Jan -.02 + .10 - -.19 + .12 .21 + .11 -.32 .11 -.29 + .17 b .37 + . I 4 a 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b, Means i n the same column s u p e r s c r i p t e d by the same l e t t e r a re not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means i n the same row u n d e r l i n e d by the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t from each other by Duncan's t e s t . 43. o o Holstein A Crossbred o Ayrshire 10 o i Aug-Sep Oct-Nov '- Dec-Jon Feb -Mar Apr-May Jun-Jul FIGURE 5. B r e e d - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t . Aug-Sep o Holstein A Crossbred Ayrshire Oct-Nov Dec-Jan F e b - M a r Apr -May J u n -Ju l FIGURE 6. B r e e d - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r l a c t a t i o n a v e r a g e p e r c e n t t o t a l o r g a n i c s o l i d s . i n Decembe r - J anua r y , w h i l e n o t s i g n i f i c a n t l y d i f f e r e n t f r om z e r o were r e l a t i v e l y l a r g e ( i n a b s o l u t e v a l u e ) . I n o r d e r t o d e t e r m i n e t h e e f f e c t o f s ea son o f c a l v i n g on l a c t a t i o n a ve r age p e r c e n t m i l k f a t f o r each b r e e d g r o u p , Duncan ' s t e s t was a p p l i e d t o t he sea son s u b c l a s s means o f each b r e e d s e p a r a t e l y ( T a b l e 1 4 ) . The H o l s t e i n s e a s o n a l means were no t s i g n i f i c a n t l y d i f f e r e n t f r om each o t h e r . Fo r c r o s s b r e d s , summer and autumn (June t o November i n c l u s i v e ) c a l v i n g was a s s o c i a t e d w i t h s i g n i f i c a n t l y h i g h e r p e r c e n t m i l k f a t l e v e l s t h a n w i n t e r and s p r i n g (December t o May i n c l u s i v e ) c a l v i n g . D i f f e r e n c e s among A y r s h i r e s e a s o n a l means, w i t h i n each o f t h e f o l l o w i n g g roups o f means, were n o t s i g n i f i c a n t : 1) A u g u s t - S e p t e m b e r , D e c e m b e r - J a n u a r y , O c t o b e r - November, J u n e - J u l y , and F e b r u a r y - M a r c h ; 2) Oc tobe r -Novembe r , J u n e - J u l y , F e b r u a r y - M a r c h , and A p r i l - M a y . S i g n i f i c a n t l y h i g h e r l a c t a t i o n a ve rage p e r c e n t m i l k f a t was a s s o c i a t e d w i t h A y r s h i r e s c a l v i n g i n Augu s t - S ep tembe r and December - Janua ry t han i n A p r i l - M a y ( T a b l e 1 4 ) . Duncan ' s t e s t on t he b r e e d g roup means, f o r each s e a s o n , showed t h a t : 1) i n J u n e - J u l y and A u g u s t - S e p t e m b e r , d i f f e r e n c e s between c r o s s b r e d and A y r s h i r e means were n o t s i g n i f i c a n t bu t b o t h means were s i g n i f i c a n t l y h i g h e r t h a n the H o l s t e i n ; 2) i n Decembe r - J anua r y , F e b r u a r y - M a r c h , and A p r i l - M a y d i f f e r e n c e s between H o l s t e i n and c r o s s b r e d means were no t s i g n i f i c a n t , bu t b o t h means were s i g n i f i c a n t l y l o w e r t h a n t h e A y r s h i r e ; 3) i n Oc tobe r -November d i f f e r e n c e s among means o f the t h r e e breed groups were not s i g n i f i c a n t (Table 14). The breed season i n t e r a c t i o n c o n s t a n t s and s u b c l a s s means (as d e v i a t i o n s from the o v e r a l l mean) f o r l a c t a t i o n average p e r c e n t t o t a l o r g a n i c s o l i d s are shown i n Table 15 and graphed i n F i g u r e 6. The c o n s t a n t s a s s o c i a t e d w i t h H o l s t e i n s c a l v i n g i n April-May and i n August-September and w i t h A y r s h i r e s i n J u n e - J u l y were s i g n i f i c a n t l y d i f f e r e n t from zero by a t - t e s t . H o l s t e i n s e a s o n a l means (percent t o t a l o r g a n i c s o l i d s ) were not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r . D i f f e r e n c e s among c r o s s b r e d s e a s o n a l means, w i t h i n each o f the f o l l o w i n g groups of means, were not s i g n i f i c a n t : 1) August- September, October-November and J u n e - J u l y ; 2) J u n e - J u l y and December-January; 3) December-January, April-May and February-March. The f o l l o w i n g comparisons o f c r o s s b r e d s e a s o n a l means were s i g n i f i c a n t : 1) August-September and October-November h i g h e r than December-January, A p r i l - M a y , and February-March; 2) J u n e - J u l y h i g h e r than A p r i l - M a y and February-March. D i f f e r e n c e s among A y r s h i r e s e a s o n a l means, w i t h i n each o f the f o l l o w i n g groups o f means, were not s i g n i f i c a n t : 1) August-September, December-January, and October-November; 2) December-January, October-November, February-March, June- J u l y , and A p r i l - M a y . The A y r s h i r e mean (pe r c e n t t o t a l o r g a n i c s o l i d ) f o r August-September c a l v i n g was s i g n i f i c a n t l y TABLE 15. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: LACTATION AVERAGE PERCENT TOTAL ORGANIC SOLIDS. A. Least Squares Constant - S.E. B. Subclass means"1 - S.E. ason 3 — - H o l s t e i n Crossbred A y r s h i r e H o l s t e i n " * Crossbred A y r s h i r e Feb - Mar .14 + .10 -.19 + .10 .05 + .09 -.40 + .12 - . 39 + .14° .16 + . l l b Apr - May .21 + .0 8* -.10 + .10 .11 + .09 -.31 + .09 -.29 + .12° .00 + .13 b Jun - J u l .16 + .10 .10 + .11 -.26 + .12* -.11 + .12 .17 + . 1 3 a b .10 + .17 b Aug - Sep -.33 + .14* .17 + .16 .16 + .18 -.29 + .14 .56 + . 2 l a .84 + .2 8 a Oct - Nov -.16 + .17 .20 + .12 -.04 + .14 -.24 + .26 .29 + .12 a .34 + . 1 7 a b Dec - Jan - -.02 + .14 -.18 + .16 .20 + .15 -.44 + .16 -.26 + .2 3 b c .42 + . 2 0 a b 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b,c Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means i n the same row u n d e r l i n e d by the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . -r CO g r e a t e r than the A y r s h i r e means f o r : February-March, June- J u l y , and April-May (Table 15). Duncan's t e s t on the breed group means (p e r c e n t t o t a l o r g a n i c s o l i d s ) f o r each season showed t h a t : 1) i n August-September and October-November, c r o s s b r e d and A y r s h i r e means d i d not d i f f e r s i g n i f i c a n t l y but were s i g n i f i c a n t l y h i g h e r than H o l s t e i n ; 2) i n December-January, February-March and A p r i l - M a y , H o l s t e i n and c r o s s b r e d means d i d not d i f f e r s i g n i f i c a n t l y but were s i g n i f i c a n t l y lower than A y r s h i r e ; 3) i n J u n e - J u l y , d i f f e r e n c e s among the means o f the th r e e breed groups were not s i g n i f i c a n t . Year by Season I n t e r a c t i o n Year by season i n t e r a c t i o n was a s i g n i f i c a n t source o f v a r i a t i o n o f l a c t a t i o n average milk f a t and t o t a l o r g a n i c s o l i d s , and accounted f o r 7% of the t o t a l v a r i a t i o n i n each o f these t r a i t s . The year season i n t e r a c t i o n c o n s t a n t s and s u b c l a s s means (as d e v i a t i o n s from the o v e r a l l mean) f o r l a c t a t i o n average p e r c e n t m i l k f a t are shown i n Table 16 and graphed i n F i g u r e 7. The i n t e r a c t i o n c o n s t a n t s i n the two seasons o f December-January and February-March were s i g n i f i c a n t l y d i f f e r e n t from zero by a t - t e s t (Table 16). Thus d i f f e r e n c e i n response t o season of f r e s h e n i n g between the two years o c c u r r e d i n the w i n t e r months. For the f i r s t y ear (August 1967 to J u l y 1968) the e f f e c t o f season o f c a l v i n g on l a c t a t i o n average per cent TABLE 16. YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: LACTATION AVERAGE PERCENT MILK FAT. A. Least Squares Constant + S.E. B. Subclass Means 1 - S.E. Season 1967 - 68 1968 - 69 1967 - 68 1968 - 69 Feb - Mar -.18 + .0 5* .18 + .05* -.38 + .08° .02 + .08 a Apr - May .07 + .05 -.07 + .05 -.13 + .07 b -.26 + .08 b Jun - J u l .08 + .06 -.08 + .06 .11 + .08 3 -.01 +• .09 a Aug - Sep .13 + .18 -.13 + .18 .39 + .13 a .16 + . l l a Oct - Nov .08 + .07 -.08 .07 .19 + .13 a .02 + .09 a Dec - Jan -.18 + .0 8* .18 + .0 8* -.27 + . l l b C .11 + .12 a i As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . a,b,c. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . o Y e a r - S e a s o n Means A Season Constants m d c a> o 0. 3 6 i A-S ÔN DTJ FTM ÂM JTJ ATS ÔN DTJ F̂M ÂM Ĵ J FIGURE 7. Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t . S e a s o n o f f r e s h e n i n g c o n s t a n t s a r e a l s o p l o t t e d . • Y e a r - S e a s o n M e a n s A S ea son Cons tan t s •s ÔN DTJ FTM ATM JIJ ATS ÔN DTJ F̂M A^M Ĵ J FIGURE 8 . Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r l a c t a t i o n a v e r a g e p e r c e n t t o t a l o r g a n i c s o l i d s . S e a s o n o f f r e s h e n i n g c o n s t a n t s a r e a l s o p l o t t e d . 50 . milk f a t was: 1) cows c a l v i n g from June t o November i n c l u s i v e d i d not d i f f e r s i g n i f i c a n t l y , but were h i g h e r i n p e r c e n t m i l k f a t than cows c a l v i n g at o t h e r times o f the y e a r ; 2) cows c a l v i n g i n April-May d i d not d i f f e r s i g n i f i c a n t l y from cows c a l v i n g i n December-January but were s i g n i f i c a n t l y h i g h e r i n p e r c e n t milk f a t than cows c a l v i n g i n February-March; and 3) cows c a l v i n g i n December-January d i d not d i f f e r s i g n i f i c a n t l y i n p e r c e n t m i l k f a t from cows c a l v i n g i n February-March. For the second y e a r (August 196 8 t o J u l y 196 9) cows c a l v i n g i n Apri l - M a y were s i g n i f i c a n t l y lower i n p e r c e n t m i l k f a t than cows c a l v i n g a t o t h e r times o f the y e a r ; cows c a l v i n g a t o t h e r seasons o f t h i s y e a r d i d not d i f f e r s i g n i f i c a n t l y i n average p e r c e n t f a t (Table 16). A t - t e s t was used t o t e s t d i f f e r e n c e s between c o r r e s p o n d i n g seasons i n the two years f o r s i g n i f i c a n c e . Cows c a l v i n g i n February-March and December-January o f the second y e a r were s i g n i f i c a n t l y h i g h e r i n average p e r c e n t m i l k f a t than cows c a l v i n g i n these two seasons i n the f i r s t y e a r . The d i f f e r e n c e s between years f o r each of the o t h e r f o u r seasons were not s i g n i f i c a n t (Table 16). However, the t r e n d was f o r s l i g h t l y lower p e r c e n t m i l k f a t i n each of these seasons i n the second y e a r , than i n the c o r r e s p o n d i n g seasons o f the f i r s t y e a r . As the second o r d e r i n t e r a c t i o n was not a s i g n i f i c a n t source o f v a r i a t i o n , breed response t o season o f f r e s h e n i n g was r e l a t i v e l y c o n s i s t e n t a c r o s s both y e a r s . The y e a r season i n t e r a c t i o n c o n s t a n t s and s u b c l a s s means (as d e v i a t i o n s from the overal.l mean) f o r l a c t a t i o n average p e r c e n t t o t a l o r g a n i c s o l i d s are shown i n Table 17 and graphed i n F i g u r e 8. For the f i r s t y ear (August 1967 to J u l y 1968 i n c l u s i v e ) Duncan's t e s t (Table 17) showed t h a t : 1) cows c a l v i n g August-September d i d not d i f f e r s i g n i f i c a n t l y i n perc e n t t o t a l o r g a n i c s o l i d s from cows c a l v i n g i n J u n e - J u l y and i n October-November but were s i g n i f i c a n t l y h i g h e r than cows c a l v i n g at o t h e r times o f t h e y e a r ; 2) cows c a l v i n g June- J u l y and October-November d i d not d i f f e r , s i g n i f i c a n t l y i n p e r c e n t t o t a l o r g a n i c s o l i d s from cows c a l v i n g i n A p r i l - M a y but were s i g n i f i c a n t l y h i g h e r than cows c a l v i n g December- January and February-March; 3) cows c a l v i n g A p r i l - M a y d i d not d i f f e r s i g n i f i c a n t l y i n per c e n t t o t a l o r g a n i c s o l i d s from cows c a l v i n g i n December-January but were s i g n i f i c a n t l y h i g h e r than cows c a l v i n g i n February-March and 4) cows c a l v i n g December- January d i d not d i f f e r s i g n i f i c a n t l y i n percent t o t a l o r g a n i c s o l i d s from cows c a l v i n g i n February-March. For the second y e a r i n t h i s study (August 1968 t o J u l y 1969 i n c l u s i v e ) season o f c a l v i n g d i d not have a s i g n i f i c a n t e f f e c t on l a c t a t i o n a l average p e r c e n t t o t a l o r g a n i c s o l i d s . The t - t e s t i n d i c a t e d t h a t cows c a l v i n g i n February- March and i n December-January o f the second y e a r were s i g n i f i c a n t l y h i g h e r i n l a c t a t i o n average p e r c e n t t o t a l o r g a n i c s o l i d s than cows c a l v i n g i n these two seasons i n the f i r s t y e a r . TABLE 1 7 . YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: LACTATION AVERAGE PERCENT TOTAL ORGANIC SOLIDS. A. Least Squares Constant + S.E. B. Subclass Means 1 - S.E. Season 1967 - 68 1968 - 69 1967 - 68 1968 - 6 g n . s . Feb - Mar -.24 + .0 7* .24 + .07* -.51 + . l l d .09 + .11 Apr - May .09 + .07 -.09 + .07 -.17 + . 0 9 b G -.23 + .11 Jun - J u l .12 + .08 -.12 + .08 .24 + . 0 9 a b -.01 + :'i2 Aug - Sep .26 + .12 -.26 + .12 .58 + .18 a .06 + .15 Oct - Nov .01 + .10 -.01 + .10 .03 + . 1 8 a b .12 + .12 Dec - Jan -.24 + .11* .24 + . 11* -.39 + . 1 5 C d .21 + .16 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b,c,d. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . The d i f f e r e n c e s between years f o r each o f the o t h e r f o u r seasons were not s i g n i f i c a n t (Table 1 7 ). Days M i l k e d and Age at P a r t u r i t i o n The c o - v a r i a b l e o f days m i l k e d was a s i g n i f i c a n t source of v a r i a t i o n f o r l a c t a t i o n average p e r c e n t milk f a t , l a c t o s e , and t o t a l o r g a n i c s o l i d s . Age at p a r t u r i t i o n was a s i g n i f i c a n t source of v a r i a t i o n f o r l a c t a t i o n average p e r c e n t l a c t o s e . The s i g n i f i c a n t p a r t i a l and standa r d p a r t i a l r e g r e s s i o n c o e f f i c i e n t s are shown i n Tab l e 18. Days milked accounted f o r 5% o f the t o t a l v a r i a t i o n i n l a c t a t i o n average p e r c e n t f a t . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t was p o s i t i v e and the value was 0.27 + 0.06 i n st a n d a r d measure and 0.0055 + 0.0013 i n p e r c e n t ; i n d i c a t i n g an i n c r e a s e i n l a c t a t i o n average m i l k f a t p e r c e n t w i t h an i n c r e a s e i n l a c t a t i o n l e n g t h . Days milked and age at p a r t u r i t i o n were both s i g n i f i c a n t e f f e c t s on l a c t a t i o n average p e r c e n t l a c t o s e and accounted f o r 6% and 11% r e s p e c t i v e l y o f the t o t a l v a r i a t i o n i n t h i s t r a i t . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t o f l a c t a t i o n average p e r c e n t l a c t o s e on number of days mi l k e d was p o s i t i v e ; 0.28 + 0.06 i n s t a n d a r d measure and 0.0024 + 0.0006 i n p e r c e n t ; i n d i c a t i n g an i n c r e a s e o f percent l a c t o s e with advancing l a c t a t i o n . T h i s f i n d i n g does not agree w i t h r e p o r t s i n the l i t e r a t u r e ; Robertson e t a l . (32) showed t h a t , w i t h i n a l a c t a t i o n , l a c t o s e tends to r i s e from p a r t u r i t i o n u n t i l a pproximately the 45 t b* day o f l a c t a t i o n a f t e r which time i t TABLE 18 PARTIAL AND STANDARD PARTIAL REGRESSION COEFFICIENTS : LACTATION AVERAGE PERCENT COMPOSITION ON DAYS MILKED AND AGE AT PARTURITION Component DAYS MILKED P e r c e n t (x I 0 " 3 ) + S.E. S t a n . Meas. + S.E. AGE P e r c e n t (x 10-3) + s.E. S t a n . Meas. + S.E, % F a t % L a c t o s e % T.O.S. 5.5 + 1.5 2.4 + 0.6 8.5 + 1.7 0.27 + 0.06 0.28 + 0.06 0.31 + 0 . 0 6 -0.11 + 0.02 -0.37 + 0.06 Onl y s i g n i f i c a n t r e g r e s s i o n c o e f f i c i e n t s a r e shown. Cn s l o w l y d e c l i n e s u n t i l l a t e l a c t a t i o n when f u r t h e r d rop s can be f a i r l y s t e e p . The d i s c r e p a n c y between t h e f i n d i n g s i n t h i s s t u d y and t h o s e r e p o r t e d i n t h e l i t e r a t u r e c o u l d be e x p l a i n e d i f y e a r e f f e c t s were g r a d u a l and c o n t i n u o u s a c r o s s t i m e due t o c h a n g i n g e n v i r o n m e n t o r management ( f o r example l o w e r l e v e l s o f m a s t i t i s ) and t h e s e i n f l u e n c e s t e n d e d t o a l t e r n o rma l l a c t a t i o n a l change s . The r e g r e s s i o n o f l a c t a t i o n a ve r age p e r c e n t l a c t o s e on age o f t h e cow a t p a r t u r i t i o n was s i g n i f i c a n t and n e g a t i v e ; i n d i c a t i n g a d e c l i n e i n p e r c e n t l a c t o s e i n m i l k p r oduced by o l d e r cows. The p a r t i a l r e g r e s s i o n c o e f f i c i e n t was - 0 . 3 7 + 0.006 i n s t a n d a r d measure and -0 .00011 + 0.00002 i n p e r c e n t . R e p o r t s i n t h e l i t e r a t u r e i n d i c a t e t h a t p e r c e n t l a c t o s e d e c l i n e s as t h e age o f t h e cow i n c r e a s e s . ( 2 , 1 5 , 3 8 ) . Days m i l k e d was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n a ve r age t o t a l o r g a n i c s o l i d s and a c c o u n t e d f o r 7% o f t h e t o t a l v a r i a t i o n . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t was 0.31 + 0.06 i n s t a n d a r d measure and 0.0085 + 0.0017 i n p e r c e n t ( T a b l e 1 8 ) . The c o - v a r i a b l e o f days m i l k e d was no t a s i g n i f i c a n t s o u r c e o f v a r i a t i o n o f l a c t a t i o n a ve r a ge p e r c e n t p r o t e i n . R e p o r t s i n t h e l i t e r a t u r e ( 3 , 38) i n d i c a t e d t h a t p e r c e n t p r o t e i n i n c r e a s e d i n l a t e l a c t a t i o n i n a manner s i m i l a r t o t h e l a c t a t i o n t r e n d f o r p e r c e n t m i l k f a t , i n w h i c h ca se t h e e x p e c t e d r e s u l t wou ld be t h a t days m i l k e d wou ld have a s i g n i f i c a n t e f f e c t on l a c t a t i o n a ve r a ge p e r c e n t p r o t e i n (as was t h e ca se w i t h p e r c e n t f a t ) . However B a i l e y (3) r e p o r t e d t h a t t h e i n c r e a s e i n p e r c e n t p r o t e i n u s u a l l y o b s e r v e d a f t e r 180-200 days i n l a c t a t i o n was a s s o c i a t e d w i t h p r e g n a n c y , and t h i s i n c r e a s e d i d no t o c c u r i n b a r r e n cows. Cows i n t h e p r e s e n t s t u d y were open f o r an u n u s u a l l y l o n g p e r i o d o f t i m e ( T a b l e 3 ) , wh i ch may e x p l a i n t he non s i g n i f i c a n t e f f e c t o f days m i l k e d on l a c t a t i o n a ve r age p e r c e n t p r o t e i n . Summary o f M i l k C o m p o s i t i o n B reed group was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r l a c t a t i o n a ve r age p e r c e n t m i l k f a t , p r o t e i n , and t o t a l o r g a n i c s o l i d s , bu t n o t f o r p e r c e n t l a c t o s e . F o r p e r c e n t p r o t e i n , A y r s h i r e and c r o s s b r e d means d i d no t d i f f e r s i g n i f i c a n t l y , bu t b o t h b r e e d group means were s i g n i f i c a n t l y h i g h e r t h a n t h e H o l s t e i n . B reed g roup was t h e o n l y s i g n i f i c a n t a f f e c t on l a c t a t i o n a ve r age p e r c e n t p r o t e i n . D i f f e r e n c e s i n l a c t a t i o n a l a ve r age p e r c e n t m i l k f a t and t o t a l o r g a n i c s o l i d s among t h e b r e e d g roups were r e l a t e d t o t h e s ea son i n wh i ch l a c t a t i o n s t a r t e d . I n g e n e r a l , A y r s h i r e means were h i g h e r t h a n H o l s t e i n f o r a l l s e a s o n s ; c r o s s b r e d means ( w i n t e r c a l v i n g ) d i d no t d i f f e r s i g n i f i c a n t l y f r o m H o l s t e i n , and c r o s s b r e d means (summer c a l v i n g ) d i d no t d i f f e r s i g n i f i c a n t l y f r o m A y r s h i r e . S ea son , b r e e d by s e a s o n , and y e a r by season were s i g n i f i c a n t s o u r c e s o f v a r i a t i o n f o r p e r c e n t m i l k f a t and p e r c e n t t o t a l o r g a n i c s o l i d s . D i f f e r e n c e s among H o l s t e i n s e a s o n a l 57. means were not s i g n i f i c a n t . Crossbreds and A y r s h i r e s (with the e x c e p t i o n o f A y r s h i r e s c a l v i n g i n December-January) c a l v i n g i n the summer tended t o have h i g h e r percentages than w i n t e r and s p r i n g c a l v e r s . D i f f e r e n c e s between summer and w i n t e r c a l v i n g was g r e a t e r f o r c r o s s b r e d s than f o r A y r s h i r e s . Less v a r i a t i o n was a s s o c i a t e d with season o f c a l v i n g i n the second year than i n the f i r s t y e a r . Means o f cows c a l v i n g i n the w i n t e r o f the second y e a r were h i g h e r i n p e r c e n t milk f a t and percent o r g a n i c s o l i d s than cows c a l v i n g i n the w i n t e r o f the f i r s t y e a r . An i n c r e a s e i n the number o f days milked was a s s o c i a t e d with a s i g n i f i c a n t i n c r e a s e i n l a c t a t i o n average p e r c e n t milk f a t , l a c t o s e and t o t a l o r g a n i c s o l i d s . A s i g n i f i c a n t d e c l i n e i n l a c t a t i o n average percent l a c t o s e was a s s o c i a t e d w i t h i n c r e a s e d age o f the cow. 58 . ENERGY RELATIONSHIPS: RESULTS AND DISCUSSION A summary o f t h e r e s u l t s o f t h e a n a l y s e s o f v a r i a n c e o f 1) p e r c e n t m i l k e n e r g y a s ; m i l k f a t , p r o t e i n and l a c t o s e ; 2) r a t i o o f m i l k f a t t o p r o t e i n ; and 3) e n e r g y c o n c e n t r a t i o n o f m i l k ( i n k c a l . p e r pound) i s p r e s e n t e d i n T a b l e 19. F o r t h e above l i s t e d t r a i t s t h e s t a t i s t i c a l model a c c o u n t e d f o r 39, 35, 40, 36, and 43 p e r c e n t r e s p e c t i v e l y o f t h e t o t a l v a r i a t i o n o f e a c h t r a i t . The o v e r a l l means, w i t h t h e i r s t a n d a r d e r r o r s , and t h e b r e e d g r o u p l e a s t s q u a r e s c o n s t a n t s , w i t h t h e i r s t a n d a r d e r r o r s a r e p r e s e n t e d i n T a b l e 20. B r e e d Group B r e e d g r o u p was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r p e r c e n t m i l k e n e r g y a s ; m i l k f a t and l a c t o s e , b u t n o t f o r p e r c e n t e n e r g y as p r o t e i n . B r e e d g r o u p means o f t h e s e t h r e e t r a i t s a r e shown g r a p h i c a l l y i n F i g u r e 9. B r e e d g r o u p was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r t h e r a t i o o f m i l k f a t t o p r o t e i n and f o r t h e e n e r g y c o n c e n t r a t i o n o f m i l k . N i n e p e r c e n t o f t h e t o t a l v a r i a t i o n o f p e r c e n t e n e r g y as m i l k f a t was a c c o u n t e d f o r by b r e e d g r o u p . S i n c e t h e i n t e r a c t i o n o f b r e e d by s e a s o n was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r t h i s t r a i t , d i f f e r e n c e s among b r e e d means were r e l a t e d t o t h e s e a s o n i n w h i c h l a c t a t i o n s t a r t e d . The l e a s t s q u a r e s means f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e g r o u p s were; 44.7 + 0.32, 45.5 + 0.30 and 47.2 + 0.36 p e r c e n t e n e r g y as f a t r e s p e c t i v e l y . The o v e r a l l mean was 45.8 + 0.19 p e r c e n t . TABLE 19. SUMMARY OF THE ANALYSES OF VARIANCE: ENERGY RELATIONSHIPS T r a i t T o t a l F i t t e d 1 T o t a l 2 0 • 5 • S • 3 3 Main E f f e c t s I n t e r a c t i o n s B r . Sn. Y r . B r . X S n . B r . X Y r . Y r . X S n . BXSXY C o - v a r i a b l e s Open M i l k e d 3 Age P e r c e n t o f e n e r g y as : a. F a t 0. 39 1 . 7 6 x l 0 3 0.09* 0.09* - 0.07* - 0.06* 0.03 - 0.04* b. P r o t e i n .35 5 . 3 9 x l 0 2 .01 .0 7*. 0 3* .0 7* - . 04 .04 .0 5* - c. L a c t o s e .40 7 . 9 0 x l 0 2 .12* .06*. 01 .04 - .05* .03 .01 .0 3* F a t / P r o t . r a t i o .36 2.95 .0 5* .09*.01 .08* - .05* .04 .0 5* - E n e r g y / l b . m i l k .43 1 . 0 3 x l 0 5 .13* .0 8* - .0 6* - .0 7* .04 .06* - Deg. o f Freedom 38 237 2 5 1 10 2 5 10 1 • I 1 1 F r a c t i o n o f s t a t i s t i c a l t h e t o t a l model ( R 2 . sums o f ' ) . s q u a r e s a c c o u n t e d f o r by f i t t i n g t h e e f f e c t s i n t h e 2 T o t a l c o r r e c t e d sums o f s q u a r e s . 3 F r a c t i o n o f t h e t o t a l sums o f m o d e l ( v a l u e s l e s s t h a n 0.01 « s q u a r e s are n o t a c c o u n t e d f o r by e a c h e f f e c t shown). i n t h e s t a t i s t i c a l S i g n i f i c a n t s o u r c e o f v a r i a t i o n . C n CO TABLE 2 0 OVERALL MEANS AND BREED GROUP LEAST SQUARES CONSTANTS ENERGY RELATIONSHIPS T r a i t O v e r a l l Mean + S.E. P e r c e n t Energy a s : . a . F a t * 4 5 . 8 + 0 . 1 9 b. P r o t e i n c . L a c t o s e F a t / P r o t e i n r a t i o 5 ' 5 n. s. 27.5 + .11 26.7 + .13 1.08 + .00< Ene rgy ( k c a l ) / l b . m i l k * 332.9 + 1 . 4 L e a s t Squares C o n s t a n t s + S .E . H o l s t e i n C r o s s b r e d A y r s h i r e - 1 .12 + 0.26 0.15 + 0.15 0.97 + 0 .17 ' -0 .26 + 0.26 1. 38 + 0 . 2 ! 0.17 + 0.15 - 0 . 3 3 + 0.15 0.08 + 0 . 1 7 b - 1 . 05 + 0 . 1 8 ° - 0 .030 + 0.011 - 0 . 013 + 0.011 -11 .9 + 2.0 •0.10 + 1.9 0.043 + 0.012 12.0 + 2.1 Breed group was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n bu t Duncan ' s t e s t was n o t used t o t e s t b r e e d means because t he b r e e d by s ea son i n t e r a c t i o n was a l s o s i g n i f i c a n t . a , b , c C o n s t a n t s s u p e r s c r i p t e d by t h e same l e t t e r a r e n o t s i g n i f i c a n t l y d i f f e r e n t n. s. f rom each o t h e r by Duncan ' s t e s t . D i f f e r e n c e s among b reeds no t s i g n i f i c a n t by t h e a n a l y s i s o f v a r i a n c e . 61. O . d lO Ls.Sq. -Mean 45.7% CD tr U J z U J o 6 UJ o tr U J a. o. d ro P. o CM Q. o a> \- to tr- io in •o CD v. - Q to to o CP C "5 to o X FAT CM CO \_ JE to V. < 8 CM T3 CD w .O to (0 O »_ o CO CM 0) +- W O X PROTEIN Ls.Sq. •Mean 27.4% CO in CM CD to >» < a> a) CM T3 CD i_ X) to to o Ls.Sq. -Mean 26.7% r> CM c '35 w o X LACTOSE FIGURE 9. L a c t a t i o n a v e r a g e p e r c e n t m i l k e n e r g y a s ; m i l k f a t , p r o t e i n and l a c t o s e f o r t h e t h r e e b r e e d g r o u p s . B r e e d g r o u p a c c o u n t e d f o r 12 p e r c e n t o f t h e t o t a l v a r i a t i o n i n p e r c e n t m i l k e n e r g y as l a c t o s e . The l e a s t s q u a r e s b r e e d g r o u p means were; 27.7 + 0.22, 26.8 + 0.20 and 25.6 + 0.24 p e r c e n t f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e r e s p e c t i v e l y . The o v e r a l l l e a s t s q u a r e s mean was 2 6.7 + 0.13 p e r c e n t . Duncan's t e s t showed t h a t a l l t h e t h r e e b r e e d g r o u p means d i f f e r e d s i g n i f i c a n t l y f r o m e a c h o t h e r . The e f f e c t o f b r e e d g r o u p a c c o u n t e d f o r 5 p e r c e n t o f t h e t o t a l v a r i a t i o n o f t h e r a t i o o f m i l k f a t t o p r o t e i n . The b r e e d by s e a s o n i n t e r a c t i o n was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n . The l e a s t s q u a r e s means f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e g r o u p s were; 1.05 + 0.014, 1.0 7 + 0.012 and 1.12 + 0.15 r e s p e c t i v e l y . The o v e r a l l l e a s t s q u a r e s mean was 1.08 + 0.008. B r e e d g r o u p a c c o u n t e d f o r 13 p e r c e n t o f t h e t o t a l v a r i a t i o n o f e n e r g y c o n c e n t r a t i o n o f m i l k . B r e e d by s e a s o n i n t e r a c t i o n was a l s o a s i g n i f i c a n t s o u r c e o f v a r i a t i o n . The l e a s t s q u a r e s means f o r H o l s t e i n , c r o s s b r e d and A y r s h i r e g r o u p s were; 321.0 + 2 . 4 1 , 332.8 + 2.21 and 344.9 + 2.72 k i l o c a l o r i e s p e r pound o f m i l k . The o v e r a l l l e a s t s q u a r e s mean was 332.9 + 1.4 k i l o c a l o r i e s p e r pound o f m i l k . S e a s o n o f C a l v i n g S e a s o n o f c a l v i n g was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n o f : 1) p e r c e n t m i l k e n e r g y a s ; m i l k f a t , p r o t e i n , and l a c t o s e ; 2) r a t i o o f m i l k f a t t o p r o t e i n ; and 3) e n e r g y c o n c e n t r a t i o n o f m i l k . F o r t h e s e t r a i t s s e a s o n o f c a l v i n g a c c o u n t e d f o r : 9, 7, 6, 9, and 8 p e r c e n t r e s p e c t i v e l y o f t h e t o t a l v a r i a t i o n . S i n c e b r e e d by s e a s o n o r y e a r by s e a s o n ( o r b o t h ) i n t e r a c t i o n s were a l s o s i g n i f i c a n t s o u r c e s o f v a r i a t i o n f o r e a c h o f t h e above l i s t e d t r a i t s , s e a s o n r e s p o n s e s v a r i e d b o t h by b r e e d and by y e a r . The s e a s o n l e a s t s q u a r e s c o n s t a n t s a r e shown i n T a b l e 21. Y e a r o f C a l v i n g Y e a r l e a s t s q u a r e s c o n s t a n t s , w i t h t h e i r s t a n d a r d e r r o r s , f o r e n e r g y r e l a t i o n s h i p s a r e shown i n T a b l e 22. Y e a r o f l a c t a t i o n s t a r t was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r p e r c e n t m i l k e n e r g y as p r o t e i n and a c c o u n t e d f o r 3 p e r c e n t o f t h e t o t a l v a r i a t i o n . The l e a s t s q u a r e s mean f o r t h e f i r s t y e a r ( A u g u s t 1967 t o J u l y 1968) was 27.8 + 0.20 p e r c e n t , b u t i n t h e s e c o n d y e a r i t d e c l i n e d t o 27.2 + 0.25 p e r c e n t . T h i s d e c l i n e was a t t r i b u t e d t o an i n c r e a s e (non s i g . ) f r o m t h e f i r s t y e a r t o t h e s e c o n d y e a r i n l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t and l a c t o s e ; and a d e c r e a s e ( n o n s i g . ) i n p e r c e n t p r o t e i n . B r e e d by S e a s o n I n t e r a c t i o n The i n t e r a c t i o n o f b r e e d by s e a s o n was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r : 1) p e r c e n t m i l k e n e r g y a s ; m i l k f a t , and p r o t e i n ; 2) r a t i o o f m i l k f a t t o p r o t e i n ; and 3) e n e r g y c o n c e n t r a t i o n o f m i l k . B r e e d by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 7 p e r c e n t o f t h e t o t a l v a r i a t i o n o f p e r c e n t m i l k e n e r g y as m i l k f a t . The l e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e shown i n T a b l e 2 3 and t h e s u b c l a s s means a r e g r a p h e d i n F i g u r e 10. TABLE 21. SEASON LEAST SQUARES CONSTANTS: ENERGY RELATIONSHIPS L e a s t Squares C o n s t a n t s + S .E . T r a i t : 1 Feb-Mar Apr -May J u n - J u l Aug-Sep Oc t -Nov Dec - J an % Ene rgy a s : a . M i l k f a t * -1 .20 + .34 -1 .15 + .32 0 .37 + . 39 1 .44 + .55 0 .95 + .50 - 0 .41 + .51 b. P r o t e i n * 0 .61 + .20 0 .62 + .18 - 0 .32 + .22 - 0 .37 + . 32 - 0 .46 + .28 - 0 .08 + .29 c . L a c t o s e * 0 .59 + .23 0 .52 + .21 - 0 .05 + .26 -1 .06 + . 37 - 0 .48 + .33 0 .48 + . 34 F a t / P r o t . r a t i o * - 0 .050 + .014 -o .051+ .013 .018 + .016 .047 + .023 .041+ .021 - 0 . 006 + .02: Energy ( k c a l ) / l b . M i l k * - 8 .10 +2 .56 - 7 .89 +2 .38 1 .99 +2 .90 13 .94 +4 .10 4 .06 +3 .70 - 4 .01 +3 .70 Season o f c a l v i n g was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n b u t Duncan ' s t e s t was n o t u sed t o t e s t season means because y e a r by sea son and/o r b r e e d by s ea son i n t e r a c t i o n s were s i g n i f i c a n t . TABLE 2 2 YEAR LEAST SQUARES CONSTANTS ENERGY RELATIONSHIPS T r a i t 1967-68 + S .E. 1968-69 + S .E. P e r c e n t Energy a s : a . F a t n , S * - 0 . 080 + 0.192 0.080 + 0.192 b. P r o t e i n * 0.324 + 0 . 1 1 0 - 0 .324 + 0.110 c . L a c t o s e n , S * - 0 .244 + 0.128 0.244 + 0.128 F a t / P r o t e i n r a t i o n , S * -0 .0132 + 0.0081 0.0132 + 0.0081 Ene rgy ( k c a l ) l b . M i l k n , S * - 1 . 15 + 1.44 1.15 + 1.44 n . s . D i f f e r e n c e s b e t w e e n y e a r s no t s i g n i f i c a n t by t h e a n a l y s i s o f v a r i a n c e . * D i f f e r e n c e s between y e a r s s i g n i f i c a n t by the a n a l y s i s o f v a r i a n c e . TABLE 23. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: PERCENT ENERGY AS MILK FAT. A. Least Squares Constant - S.E. B. Subclass means - S.E. n s H o l s t e i n Crossbred A y r s h i r e H o l s t e i n * * Cr o s s b r e d A y r s h i r e Feb - Mar .23 + .48 - 1 . 0 7 + . 5 0 * .84 + .48 -2 .09 + . 58 -2 .52 + . 6 6 b 1.02 + . 54 Apr - May .90 + . 4 1 * - .54 + .46 - . 3 5 + .48 - 1 . 3 4 + .41 - 1 . 9 5 + . 5 8 b - .12 + .60 Jun - J u l - . 4 8 + .49 .85 + .52 - . 3 7 + .58 - 1 . 0 1 + .56 .96 + . 6 4 a 1.38 + .80 Aug - Sep - 1 . 0 0 + .67 1.37 + .77 - . 3 7 + .89 - 1 . 0 8 + .66 2.55 + i . o i a 2 .44 + 1.34 Oct - Nov .50 + .81 .72 + .60 - 1 . 2 2 + .67 .33 + 1 .26 1.41 + . 5 7 a 1.10 + .82 Dec Jan - .14 + . 66 - 1 . 34 + .77 1.48 + .73* - 1 . 6 7 + .74 - 2 . 0 0 + 1 . 0 9 b 2.45 + .95 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means i n the same row u n d e r l i n e d by the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . C D a Holstein A Crossbred o Ayrshire Oct-Nov Dec-Jan Feb-Mar Aug-Sep Apr- May Jun-Jul FIGURE 10. B r e e d - s e a s o n l e a s t s q u a r e s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r p e r c e n t m i l k e n e r g y as m i l k f a t . a Holstein A - Crossbred o Ayrshire q cvj q i Aug-Sep Oct-Wov Dec-Jan Feb-Mar Apr-May Jun-Jul FIGURE 11. B r e e d - s e a s o n l e a s t s q u a r e s f r o m t h e o v e r a l l mean, f o r as p r o t e i n . means, as d e v i a t i o n s p e r c e n t m i l k e n e r g y 68 The i n t e r a c t i o n c o n s t a n t s a s s o c i a t e d w i t h ; 1) H o l s t e i n s c a l v i n g i n A p r i l - M a y , 2) c r o s s b r e d s - c a l v i n g i n F e b r u a r y - M a r c h , and 3) A y r s h i r e s c a l v i n g i n December- J a n u a r y were s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o by a t - t e s t . Duncan's t e s t on e f f e c t o f s e a s o n o f c a l v i n g f o r e a c h b r e e d g r o u p showed t h a t t h e s e a s o n a l means o f t h e ; 1) H o l s t e i n s were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m e a c h o t h e r : 2) A y r s h i r e s were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m e a c h o t h e r ; and 3) c r o s s b r e d s c a l v i n g J u n e t o November i n c l u s i v e were s i g n i f i c a n t l y h i g h e r t h a n t h e s e a s o n a l means o f t h e c r o s s b r e d s c a l v i n g December t o May i n c l u s i v e ( T a b l e 2 3 ) . Duncan's t e s t on t h e b r e e d g r o u p means, f o r e a c h s e a s o n showed t h a t ; 1) i n J u n e - J u l y and A u g u s t - S e p t e m b e r d i f f e r e n c e s b etween A y r s h i r e and c r o s s b r e d means were non s i g n i f i c a n t b u t b o t h were s i g n i f i c a n t l y h i g h e r t h a n H o l s t e i n ; 2) i n D e c e m b e r - J a n u a r y and F e b r u a r y - M a r c h d i f f e r e n c e s between H o l s t e i n and c r o s s b r e d means were non s i g n i f i c a n t b u t b o t h were s i g n i f i c a n t l y l o w e r t h a n A y r s h i r e ; 3) i n A p r i l - M a y d i f f e r e n c e s between H o l s t e i n and b o t h t h e c r o s s b r e d and A y r s h i r e were non s i g n i f i c a n t , b u t d i f f e r e n c e s between c r o s s - b r e d and A y r s h i r e were s i g n i f i c a n t ; U) i n O c t o b e r - N o v e m b e r d i f f e r e n c e s among means o f t h e t h r e e b r e e d g r o u p s were non s i g n i f i c a n t ( T a b l e 2 3 ) . B r e e d by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 7 p e r c e n t o f t h e t o t a l v a r i a t i o n o f p e r c e n t m i l k e n e r g y as p r o t e i n . Th l e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means (as d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e shown i n T a b l e 24 a n d t h e s u b c l a s s means a r e g r a p h e d i n F i g u r e 11. The i n t e r a c t i o n c o n s t a n t s a s s o c i a t e d w i t h ; 1) H o l s t e i n s c a l v i n g i n A p r i l - M a y ; 2) c r o s s b r e d s c a l v i n g i n J u n e - J u l y , and 3) A y r s h i r e s c a l v i n g i n D e c e m b e r - J a n u a r y were s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o by a t - t e s t . The r e s u l t s o f Duncan's t e s t on t h e s e a s o n a l means f o r e a c h b r e e d g r o u p a r e p r e s e n t e d i n T a b l e 24. P l o l s t e i n s e a s o n a l means were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m e a c h o t h e r . F o r b o t h t h e c r o s s b r e d and A y r s h i r e w i n t e r c a l v i n g was a s s o c i a t e d w i t h h i g h e r p e r c e n t e n e r g y as p r o t e i n v a l u e s t h a n w i n t e r c a l v i n g ; a l t h o u g h d i f f e r e n c e s between summer and w i n t e r were g r e a t e r f o r t h e c r o s s b r e d t h a n f o r t h e A y r s h i r e . Duncan's t e s t on t h e b r e e d g r o u p means f o r e a c h s e a s o n showed t h a t ; 1) i n F e b r u a r y - M a r c h d i f f e r e n c e s b etween H o l s t e i n and A y r s h i r e means were n o t s i g n i f i c a n t b u t means o f b o t h g r o u p s were s i g n i f i c a n t l y h i g h e r t h a n t h e c r o s s b r e d , 2) i n D e c e m b e r - J a n u a r y d i f f e r e n c e s between H o l s t e i n and c r o s s - b r e d means were n o t s i g n i f i c a n t b u t t h e means o f b o t h g r o u p s were s i g n i f i c a n t l y l o w e r t h a n t h e A y r s h i r e , 3) i n t h e f o u r s e a s o n s f r o m A p r i l t o November i n c l u s i v e d i f f e r e n c e s among means o f t h e t h r e e b r e e d g r o u p s were n o t s i g n i f i c a n t ( T a b l e 24) The b r e e d by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 8 p e r c e n t o f t h e t o t a l v a r i a t i o n o f t h e r a t i o o f m i l k f a t t o p r o t e i n . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s 'TABLE 24. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: PERCENT ENERGY AS PROTEIN. A. Least Squares Constant - S.E. B. Subclass means - S.E. Ti S H o l s t e i n Crossbred A y r s h i r e H o l s t e i n ' ' C r o s s b r e d A y r s h i r e Feb - Mar -.11 + .27 .57 + .29 .46 + .27 .66 + .34 1.36 + .38 a -.18 ± . 3 1 a b Apr - May -.46 + .2 2* .30 + .27 .16 + .27 .31 + .24 1.10 + .33 a .46 + .34 a Jun - J u l .25 + .28 -.62 + .30* .37 + .33 .08 + .24 - .76 + .37 b -.28 + . 4 6 a D Aug - Sep .18 + . 38 -.56 + .44 .38 + .51 -.04 + . 38 - .75 + .58 b -.31 + . 7 7 a b Oct - Nov -.31 + .47 -.29 + .34 .60 + .39 -.62 + .72 - .59 + .33 b -.19 + .4 7 a b Dec - J a n .45 + . 38 .61 + .44 -1.06 + .42* .52 + .43 .70 + .6 3 a b -1.47 + .54 b ft 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means i n the same row u n d e r l i n e d by the same l i n e a re not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . 71. d e v i a t i o n f r o m t h e o v e r a l l mean) a r e shown i n T a b l e 2 5 and t h e s u b c l a s s means a r e g r a p h e d i n F i g u r e 12. The r e s u l t s o f Duncan's t e s t on t h e s e a s o n a l means f o r e a c h b r e e d g r o u p and on t h e b r e e d g r o u p means f o r e a c h s e a s o n a r e p r e s e n t e d i n T a b l e 25. The r e s u l t s a r e s i m i l a r t o t h o s e o b t a i n e d f o r p e r c e n t e n e r g y as m i l k f a t ( T a b l e 2 3 ) . The b r e e d by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 6 p e r c e n t o f t h e t o t a l v a r i a t i o n o f e n e r g y c o n c e n t r a t i o n o f t h e m i l k . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e p r e s e n t e d i n T a b l e 2 6 and a r e g r a p h e d i n F i g u r e 13. The r e s u l t s o f Duncan's t e s t on t h e s e a s o n a l means f o r e a c h b r e e d g r o u p and on t h e b r e e d g r o u p means f o r e a c h s e a s o n a r e s i m i l a r t o t h o s e o b t a i n e d f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t as c a n be s e e n by c o m p a r i n g T a b l e 14 w i t h T a b l e 26. Y e a r by S e a s o n I n t e r a c t i o n The i n t e r a c t i o n o f y e a r by s e a s o n was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r ; 1) p e r c e n t m i l k e n e r g y a s : m i l k f a t and l a c t o s e , 2) r a t i o o f m i l k f a t t o p r o t e i n , and 3) e n e r g y c o n c e n t r a t i o n o f t h e m i l k . Y e a r by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 6 p e r c e n t o f t h e t o t a l v a r i a t i o n o f p e r c e n t e n e r g y as m i l k f a t . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e shown i n T a b l e 2 7 and a r e g r a p h e d i n F i g u r e 14. ' The l e a s t s q u a r e s c o n s t a n t i n F e b r u a r y - M a r c h TABLE 25. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: RATIO OF MILK FAT TO PROTEIN. A. Least Squares Constant - S.E. B. S u b c l a s s means - S.E. Ti S H o l s t e i n Crossbred A y r s h i r e H o l s t e i n * * Crossbred A y r s h i r e Feb - Mar .009 + .020 -.045 + .021* .035 + .020 --.070 + .025 -.107 + .028 b .029 + .02 3 a b Apr - May .036 + .017* -.022 + .019 -.014 + .02 0 --.045 + .017 -.086 + .024 b--.022 + .025 b Jun - J u l -.019 + .020 .042 + .022 -.023 + .024 --.030 + .024 .048 + .027 a .039 + .0 3 4 d b Aug - Sep -.029 + .028 .051 + .033 -.023 + .037 --.012 + .028 .085 + .042 a .067 + .056 a b Oct - Nov .024 + .034 .027 .025 -.051 + .028 .035 + .053 .056 + .024 a .033 + .035 a b Dec - Jan -.022 + .028 -.054 + .032 .076 + .0 30*--.058 + .031 -.073 + .0»*Sb .113 + .040 a 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means i n the same row u n d e r l i n e d by .the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . D Holstein A Crossbred o Ayrshire Dec-Jan Feb-Mar Jun-Jul Aug-S-ep Oct-Nov Apr-May FIGURE 12. B r e e d - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r t h e r a t i o o f m i l k f a t t o p r o t e i n . • Holstein A Crossbred o Ayrshire Feb-Mar Aug-Sep Oct-Nov Dec-Jan Apr-May Jun-Jul FIGURE 13. B r e e d - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r t h e e n e r g y c o n - c e n t r a t i o n o f t h e m i l k ( k i l o c a l o r i e s p e r p o u n d ) . TABLE 26. BREED BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: ENERGY (KCAL) PER POUND OF MILK. A. Least Squares Constant - S.E. B. Subclass means - S.E. eason :— — — n s Holstein Crossbred Ayrshire Holstein * ' Crossbred Ayrshire Feb -- Mar 4.5 + 3.6 -7.4 + 3.6* 3.0 + 3.5 -15 .6 + 4.4 -15.6 + 4.9 b 6.9 + 4.0 a b Apr -- May 7.8 + 3.0* -3.9 + 3.5 -3.9 + 3.6 -12.1 + 3.1 -11.8 + 4.3 b 0.2 + 4.5 b Jun -- J u l 3.6 + 3.6 4.3 + 3.9 -7.9 + 4.3 - 6.4 + 4.2 6.2 + 4.8 a 6.1 + 6.0 a b Aug -- Sep -12.0 + 5.0* 7.7 5.8 4.4 + 6.7 -10.1 + 4.9 21.5 + 7.5 a 30 . 3 + 9.9 a Oct -- Nov - 3.5 + 6.1 7.2 + 4.5 -3.7 + 5.0 -11.4 + 9.4 11.2 + 4.3 a 12.4 + 6.2 a b Dec --Ja n - 0.3 + 5.0 -7.9 + 5.7 8.2 + 5.4 -16. 3 + 5.6 -11.9 + 8.2b 16 .2 + 7 . l a b i 1 As deviations from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n this column are not s i g n i f i c a n t l y d i f f e r e n t from each other by Duncan's t e s t . a,b. Means i n the same column superscripted by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each other by Duncan's t e s t . Means i n the same row underlined by the same l i n e are not s i g n i f i c a n t l y d i f f e r e n t from each other by Duncan's t e s t . TABLE 27. YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: PERCENT MILK ENERGY AS MILK FAT. + 1 + A. Least Sq uares Constant S.E. B. Subclass Means - S.E. Season 1967 -- 68 1968 69 1967 -- 68 1968 - 69 Feb - Mar -1.13 + .34* 1.13 + . 34* -2.25 + . 5 1 d 0.15 + .54 a Apr - May .48 + .33 - .48 + . 33 -0. 74 + . 4 5 b C -1.55 + .51 b Jun - J u l .40 + . 38 - .40 + . 38 0.68 + . 5 6 a b 0.06 + .59 a Aug - Sep .43 + .56 - .43 + .56 1.78 + . 8 7 a 1.09 + . 7 l a Oct - Nov .84 + .49 - .84 + .49 1.71 + . 8 5 a 0.19 + .57 a Dec - Jan -1.00 + .51 1.00 + .51 -1.49 + . 7 1 c d 0.68 + .78 a 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . a,b,c,d. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . 76 . O o Y e a r - S e a s o n Means A Sea son Constants CM II • A^S O^N bTj F^M A -M J-J A~^S O^N b D F^M A^M T-J FIGURE 14. Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r p e r c e n t m i l k e n e r g y as m i l k f a t . S e a s o n o f f r e s h e n i n g c o n s t a n t s a r e a l s o p l o t t e d . o q cvi o n CM l a Y e a r - Sea son Means A Season Constants A-^S O^N bTJ F^M A^M JTJ A^S 0^N~ F ' M A - M J-J FIGURE 15. Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r p e r c e n t m i l k e n e r g y as l a c t o s e . S e a s o n o f f r e s h e n i n g c o n s t a n t s a r e a l s o p l o t t e d . s e a s o n was s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o by a t - t e s t . Duncan's t e s t showed t h a t d i f f e r e n c e s among f i r s t y e a r s e a s o n a l means, w i t h i n e a c h o f t h e f o l l o w i n g g r o u p s o f means ( r a n k e d i n d e s c e n d i n g o r d e r b o t h w i t h i n and between g r o u p s ) were non s i g n i f i c a n t ; 1) A u g u s t - S e p t e m b e r , O c t o b e r - November, and J u n e - J u l y , 2) J u n e - J u l y and A p r i l - M a y , 3) A p r i l - M a y and D e c e m b e r - J a n u a r y , and 4) D e c e m b e r - J a n u a r y and F e b r u a r y - M a r c h . I n t h e s e c o n d y e a r t h e A p r i l - M a y s e a s o n mean was s i g n i f i c a n t l y l o w e r t h a n a l l o t h e r s ( T a b l e 2 7 ) . A t - t e s t showed t h a t t h e F e b r u a r y - M a r c h mean p e r c e n t e n e r g y as m i l k f a t was s i g n i f i c a n t l y l o w e r i n t h e f i r s t y e a r t h a n i n t h e s e c o n d y e a r . D i f f e r e n c e s between y e a r s f o r e a c h o f t h e o t h e r f i v e s e a s o n s were n o t s i g n i f i c a n t . E x c e p t f o r t h e s e a s o n s o f D e c e m b e r - J a n u a r y and F e b r u a r y - M a r c h , v a l u e s i n t h e s e c o n d t e n d e d t o be s l i g h t l y l o w e r t h a n i n t h e f i r s t y e a r . The y e a r by s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 5 p e r c e n t o f t h e t o t a l v a r i a t i o n i n p e r c e n t e n e r g y as l a c t o s e . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means a r e p r e s e n t e d i n T a b l e 2 8 and g r a p h e d i n F i g u r e 15. Duncan's t e s t showed t h a t d i f f e r e n c e s among f i r s t y e a r s e a s o n a l means, w i t h i n e a c h o f t h e f o l l o w i n g g r o u p s o f means ( r a n k e d i n d e s c e n d i n g o r d e r b o t h w i t h i n and between g r o u p s ) were n o t s i g n i f i c a n t ; 1) F e b r u a r y - M a r c h and December- J a n u a r y , 2) D e c e m b e r - J a n u a r y , A p r i l - M a y and J u n e - J u l y , 3) A p r i l - M a y , J u n e - J u l y and O c t o b e r - N o v e m b e r , 4) J u n e - J u l y , O c t o b e r - N o v e m b e r and A u g u s t - S e p t e m b e r . D i f f e r e n c e s among t h e TABLE 28. YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: PERCENT MILK ENERGY AS LACTOSE. + 1 A. Least Squares Constant S.E. B. Subclass Means - S.E. Season 1967 - 68 1968 - 69 1967 -- 68 1968 - g g n . s . Feb - Mar .73 + .2 3* -.73 + .2 3* 1.08 + . 34 a 0 .10 + . 36 Apr - May -.21 + .22 .21 + .22 0.07 + . 3 0 b c 0.97 + . 34 Jun - J u l -.14 + .25 .14 + . 25 -0.43 + . 3 ? b c d 0 . 33 + . 39 Aug - Sep -.43 + .37 .43 + . 37 -1.74 + . 58 d -0. 39 + .47 Oct - Nov -.50 + .32 .50 + .32 -1.23 + . 5 7 c d 0.26 + . 38 Dec - Jan .54 + .34 -.54 + . 34 0.78 + . 4 7 a b 0.19 + .52 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . n.s. Means i n t h i s column are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . a,b,c,d. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . s e c o n d y e a r s e a s o n a l means were n o t s i g n i f i c a n t ( T a b l e 2 8 ) , The f i r s t y e a r F e b r u a r y - M a r c h mean was s i g n i f i c a n t l y h i g h e r t h a n t h e mean o f t h i s s e a s o n i n t h e s e c o n d y e a r ; t h e f i r s t y e a r A p r i l - M a y mean was s i g n i f i c a n t l y l o w e r t h a n t h e mean o f t h i s s e a s o n i n t h e s e c o n d y e a r , by a t - t e s t . D i f f e r e n c e s between y e a r s f o r e a c h o f t h e o t h e r f o u r s e a s o n s were n o t s i g n i f i c a n t . The y e a r s e a s o n i n t e r a c t i o n a c c o u n t e d f o r 5 p e r c e n t o f t h e t o t a l v a r i a t i o n i n t h e r a t i o o f m i l k f a t t o p r o t e i n . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e p r e s e n t e d i n T a b l e 2 9 and a r e g r a p h e d i n F i g u r e 16. The r e s u l t s o f Duncan's t e s t on t h e s e a s o n a l means f o r e a c h y e a r and on y e a r means f o r e a c h s e a s o n a r e p r e s e n t e d i n T a b l e 29. The r e s u l t s a r e s i m i l a r t o t h o s e f o r p e r c e n t e n e r g y as m i l k f a t . ( T a b l e 2 7 ) . The i n t e r a c t i o n o f y e a r by s e a s o n a c c o u n t e d f o r 7 p e r c e n t o f t h e t o t a l v a r i a t i o n i n t h e e n e r g y c o n c e n t r a t i o n o f t h e m i l k ( k c a l . p e r l b . ) . L e a s t s q u a r e s c o n s t a n t s and s u b c l a s s means ( a s d e v i a t i o n s f r o m t h e o v e r a l l mean) a r e p r e s e n t e d i n T a b l e 30 and a r e g r a p h e d i n F i g u r e 17. The r e s u l t s o f Duncan's t e s t on t h e s e a s o n a l means f o r e a c h y e a r and on t h e y e a r means f o r e a c h s e a s o n a r e s i m i l a r t o t h o s e o b t a i n e d f o r l a c t a t i o n a v e r a g e p e r c e n t m i l k f a t as c a n be s e e n by c o m p a r i n g T a b l e 16 w i t h T a b l e 30 and F i g u r e 7 w i t h F i g u r e 17. The s i m i l a r i t y i n t h e r e s u l t s f o r t h e s e two t r a i t s was a t t r i b u t e d t o t h e h i g h p o s i t i v e c o r r e l a t i o n TABLE 29. YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: RATIO OF MILK FAT TO PROTEIN. A. Least Squares + Constant - S.E. B. Subclass M 1  + Means S.E. Season 1967 -- 68 1968 - 69 1967 -- 68 1968 - 69 Feb - Mar -.039 + . 014* .039 + .014* -.101 + .021° .002 + . 023 a Apr - May .020 + . 014 -.020 + .014 -.045 + .018 b c -.058 + .022 b Jun - J u l .020 + . 016 -.020 + .016 .026 + . 0 2 3 a b .012 + . 025 a Aug - Sep .008 + . 023 -.008 + .023 .041 + . 0 3 7 a b .052 + .030 a Oct - Nov .031 + . 021 -.031 + .021 .059 + .036 a .023 + .024 a Dec - Jan -.040 021 .040 + .021 -.060 + . 0 3 0 b c .048 + .033 a 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . a,b,c. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . Y e a r - S e a s o n Means Season Constants FIGURE 16. Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r t h e r a t i o o f m i l k f a t t o p r o t e i n . S e a s o n o f f r e s h e n i n g c o n - s t a n t s a r e a l s o p l o t t e d . §1 Y e a r - S e a s o n Means S e a s o n Constants FIGURE 17. Y e a r - s e a s o n s u b c l a s s means, as d e v i a t i o n s f r o m t h e o v e r a l l mean, f o r t h e e n e r g y c o n - c e n t r a t i o n o f t h e m i l k . S e a s o n o f f r e s h e n i n g c o n s t a n t s a r e a l s o p l o t t e d . TABLE 30. YEAR BY SEASON INTERACTION LEAST SQUARES CONSTANTS AND SUBCLASS MEANS, AS DEVIATIONS FROM THE OVERALL MEAN: ENERGY (KCAL) PER POUND MILK. A. Least Squares Constant + S.E. B. Subclass Means 1 - S.E. Season 19 6 7 - 68 1968 - 69 1967 -- 68 1968 - 69 Feb - Mar -9.1 + 2 .6 * 9.1 + 2 .6 * -18.3 + 3.8 d 2.2 + 4.0 a Apr - May 3.2 + 2.5 -3.2 + 2.5 - 5.8 + 3 . 3 b c -9.9 + 3.8 b Jun - J u l 4.1 + 2.8 -4.1 + 2.8 4.9 + 4 . 2 a b -1.0 + 4 . 4 a b Aug - Sep 8.6 + 4.2* -8.6 + 4.2* 21.4 + 6.5 a 6.5 + 5.3 a Oct - Nov 2.1 + 3.7 -2.1 + 3.7 5.0 + 6.4 a b 3.2 + 4.2 a Dec - Jan -8.9 + 3.8* 8.9 + 3.8* -14.1 + 5 . 3 c d 6.1 + 5.8 a 1 As d e v i a t i o n s from the o v e r a l l mean. * Constant d i f f e r e d s i g n i f i c a n t l y from zero by a t - t e s t . a,b,c,d. Means i n the same column s u p e r s c r i p t e d by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t from each o t h e r by Duncan's t e s t . Means ( i n the same row) t h a t are not u n d e r l i n e d are s i g n i f i c a n t l y d i f f e r e n t by a t - t e s t . 83 . between p e r c e n t m i l k f a t and e n e r g y c o n c e n t r a t i o n o f m i l k . Days m i l k e d and Age a t P a r t u r i t i o n Days m i l k e d was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r ; 1) p e r c e n t m i l k e n e r g y a s ; m i l k f a t and p r o t e i n , 2) r a t i o o f m i l k f a t t o p r o t e i n , and 3) e n e r g y c o n c e n t r a t i o n o f t h e m i l k . T h i s c o - v a r i a b l e a c c o u n t e d f o r 4, 5, 5, and 6 p e r c e n t o f t h e t o t a l v a r i a t i o n o f t h e above l i s t e d t r a i t s r e s p e c t i v e l y . Age a t p a r t u r i t i o n was s i g n i f i c a n t f o r p e r c e n t e n e r g y as l a c t o s e and a c c o u n t e d f o r 3 p e r c e n t o f t h e t o t a l v a r i a t i o n o f t h i s t r a i t . S i g n i f i c a n t p a r t i a l r e g r e s s i o n c o e f f i c i e n t s a r e shown i n T a b l e 31. The p a r t i a l r e g r e s s i o n c o e f f i c i e n t a s s o c i a t e d w i t h t h e r e g r e s s i o n o f p e r c e n t e n e r g y as f a t on d a y s m i l k e d was; 0.031 + 0.008 i n p e r c e n t and 0.24 + 0.06 i n s t a n d a r d measure. The r e g r e s s i o n s o f ; t h e r a t i o o f m i l k f a t t o p r o t e i n and e n e r g y c o n c e n t r a t i o n o f t h e m i l k were a l s o s i g n i f i c a n t and p o s i t i v e . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s ( s t a n d a r d measure i n p a r e n t h e s e s ) were 0.0014 + 0.0004 (.26 + .07) and 0.29 + 0.06 (0.29 + 0.06) r e s p e c t i v e l y . The p a r t i a l r e g r e s s i o n c o e f f i c i e n t s a s s o c i a t e d w i t h t h e r e g r e s s i o n o f p e r c e n t e n e r g y as p r o t e i n on days m i l k e d was -0.020 + 0.05 i n p e r c e n t and -0.28 + 0.07 i n s t a n d a r d m e asure. The p a r t i a l r e g r e s s i o n c o e f f i c i e n t a s s o c i a t e d w i t h t h e r e g r e s s i o n o f p e r c e n t ' e n e r g y as l a c t o s e on age a t p a r t u r i t i o n was -0.00058 + 0.00018 i n p e r c e n t and -0.20 + 0.06 i n s t a n d a r d m e a s u r e . T h i s d e c l i n e i n p e r c e n t e n e r g y as l a c t o s e a s s o c i a t e d w i t h i n c r e a s e d age was a t t r i b u t e d t o t h e 84 . d e c l i n e i n p e r c e n t l a c t o s e a s s o c i a t e d w i t h i n c r e a s e d age ( T a b l e 1 8 ) . Summary o f E n e r g y R e l a t i o n s h i p s B r e e d , s e a s o n , b r e e d by s e a s o n , y e a r by s e a s o n and d a y s m i l k e d were s i g n i f i c a n t f o r p e r c e n t m i l k e n e r g y as m i l k f a t , t h e r a t i o o f m i l k f a t t o p r o t e i n and t h e e n e r g y c o n c e n t r a t i o n o f t h e m i l k . A y r s h i r e means were h i g h e r t h a n H o l s t e i n f o r a l l s e a s o n s . F o r w i n t e r c a l v i n g , c r o s s b r e d means d i d n o t d i f f e r s i g n i f i c a n t l y f r o m H o l s t e i n ; b u t f o r summer c a l v i n g , c r o s s b r e d means d i d n o t d i f f e r s i g n i f i c a n t l y f r o m A y r s h i r e . D i f f e r e n c e s among H o l s t e i n s e a s o n a l means were non s i g n i f i c a n t . C r o s s b r e d s and A y r s h i r e s c a l v i n g i n t h e summer t e n d e d t o h a v e h i g h e r v a l u e s t h a n w i n t e r o r s p r i n g c a l v e r s ( e x c e p t A y r s h i r e s i n D e c e m b e r - J a n u a r y ) . Means o f w i n t e r c a l v i n g cows were h i g h e r i n t h e s e c o n d y e a r t h a n i n t h e f i r s t y e a r . S e a s o n , y e a r , b r e e d by s e a s o n and days m i l k e d were s i g n i f i c a n t f o r p e r c e n t m i l k e n e r g y as p r o t e i n . H i g h e r v a l u e s were a s s o c i a t e d w i t h w i n t e r c a l v i n g t h a n summer c a l v i n g and t h e e f f e c t o f s e a s o n was g r e a t e r on t h e c r o s s b r e d s t h a n on t h e o t h e r two b r e e d g r o u p s . B r e e d , s e a s o n , y e a r by s e a s o n and age were s i g n i f i c a n t f o r p e r c e n t e n e r g y as l a c t o s e . B r e e d means were a l l s i g n i f i - c a n t l y d i f f e r e n t f r o m e a c h o t h e r . H i g h e r v a l u e s were a s s o c i a t e d w i t h w i n t e r c a l v i n g and t h e d i f f e r e n c e s were g r e a t e r i n t h e f i r s t y e a r t h a n i n t h e s e c o n d y e a r . TABLE 31 PARTIAL AND STANDARD PARTIAL REGRESSION COEFFICIENTS : ENERGY RELATIONSHIPS ON DAYS MILKED AND AGE AT PARTURITION DAYS MILKED AGE T r a i t M e a s . „ S t a n . M e a s . 0 S t a n . U n i t s + S.E. Meas. + S.E. U n i t s + S.E. Meas. + S.E. P e r c e n t e n e r g y a s : a. F a t 0.031 + 0.008 0.24 + 0.06 b. P r o t e i n -0.020 + 0.005 -0.28 + 0.07 c . L a c t o s e F a t / P r o t e i n r a t i o 0.0014+ 0.0004 0.26 + 0.07 E n e r g y ( k c a l ) / l b . m i l k 0.29 + 0.06 0.29 + 0.06 -0.00058 + 0.00018 -.20+ 0.06 1 2 O n l y s i g n i f i c a n t r e g r e s s i o n c o e f f i c i e n t s U n i t s i n w h i c h t h e t r a i t was me a s u r e d . a r e shown. 86. CORRELATIONS BETWEEN PERFORMANCE TRAITS P h e n o t y p i c c o r r e l a t i o n s b e t w e e n a l l p e r f o r m a n c e t r a i t s s t u d i e d were c a l c u l a t e d and a r e p r e s e n t i n T a b l e 32. The c o r r e l a t i o n b etween a l l y i e l d t r a i t s were h i g h and p o s i t i v e , r a n g i n g f r o m .84 between y i e l d s o f f a t and m i l k t o .99 between y i e l d s o f l a c t o s e and m i l k . The c o r r e l a t i o n between p e r c e n t f a t and y i e l d s o f b o t h m i l k and l a c t o s e were low and n e g a t i v e a n d t h e c o e f f i c i e n t s were -.21 and -.20 r e s p e c t i v e l y . P e r c e n t f a t was p o s i t i v e l y c o r r e l a t e d w i t h y i e l d o f f a t (.33). P e r c e n t p r o t e i n a l s o showed a low n e g a t i v e c o r r e l a t i o n o f y i e l d s o f m i l k and l a c t o s e and t h e c o e f f i c i e n t was -.25 i n b o t h c a s e s . The c o r r e l a t i o n between p e r c e n t p r o t e i n and y i e l d o f p r o t e i n was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o ; b u t p e r c e n t p r o t e i n was s i g n i f i c a n t l y c o r r e l a t e d w i t h p e r c e n t f a t ( .45) . P e r c e n t l a c t o s e was n o t s i g n i f i c a n t l y c o r r e l a t e d w i t h y i e l d s o f m i l k , f a t o r p r o t e i n b u t was w i t h y i e l d s o f l a c t o s e ( .27), t o t a l o r g a n i c s o l i d s (.18) a n d t o t a l e n e r g y (.16). P e r c e n t l a c t o s e was n o t s i g n i f i c a n t l y c o r r e l a t e d w i t h t h e p e r c e n t o f f a t o r t h e p e r c e n t o f p r o t e i n . P e r c e n t e n e r g y as f a t showed a h i g h p o s i t i v e c o r r e l a t i o n (.96) w i t h p e r c e n t f a t and a low p o s i t i v e c o r r e l a - t i o n w i t h p e r c e n t p r o t e i n (.23). P e r c e n t e n e r g y as p r o t e i n was n e g a t i v e l y c o r r e l a t e d w i t h b o t h p e r c e n t f a t (-.66) and p e r c e n t l a c t o s e (-.33) and a l s o w i t h p e r c e n t e n e r g y as f a t TABLE 32 PHENOTYPIC CORRELATIONS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 l . M i l k y l d . 1.00 2 . F a t y l d . .84* 1.00 3 . P r o t . y l d . .96* . 87* 1.00 4 . L a c t . y l d . .99* .84* • .94* 1.00 5.TOS y l d . .9 7* .9 3* .9 7* .97* I.00 6 . E n e r g y y l d . .95* .96* .96* . 95* .99* 1.00 7.% F a t -.21 * .3 3* -.09 -.20* -.01 .08 1.00 • 8..% P r o t e i n -.25* .00 .03 -.25* -.10 -.07 .45* 1.00 9.% L a c t o s e .11 .13 -.09 .27* .18* .16* .06 -.10 1.00 10.% TOS -.21* .29* -.03 -.15* .02 .09 .91* .65' * .33* 1.00 11.% E n . f a t -.17* . 3 6* -.11 -.18* .01 .09 .9 6* .23 *-.0 6 .7 7* I.00 12.% E n . p r o t . -.01 -.37* - .09 -.06 -.12 -.17* -.66* .34' *-.3 3* -.4 8* -,7 7" 1.00 13.% E n . l a c t . .2 5* -.2 3* .09 .31* .09 .01 -.8 8* -.63 * .3 7* -.75* -.85* . 33* 1.00 1 4 . F a t / p r o t . -.10 ,38* -.12 -.08 .05 .13 .8 6* -.05 .12 .6 6* .9 4* -.9 3* - .64* 1.00 1 5 . K c a l / l b . m i l k -.22* . 30* -.06 -.19* .00 .08 .9 7* .62 * .18* .9 8* .85* -.52* . 84* . 74* 1 2 i 3 4 5 6 7 8 9 10 11 12 13 14 15 15 (-.77). P e r c e n t e n e r g y as p r o t e i n was p o s i t i v e l y c o r r e l a t e d w i t h p e r c e n t p r o t e i n (.34). P e r c e n t e n e r g y as l a c t o s e was a l s o n e g a t i v e l y c o r r e l a t e d w i t h t h e p e r c e n t i n t h e m i l k o f t h e o t h e r two c omponents; t h e c o r r e l a t i o n s w e r e : -.88 w i t h p e r c e n t f a t and -'.6 3 w i t h p e r c e n t p r o t e i n . P e r c e n t e n e r g y as l a c t o s e was p o s i t i v e l y c o r r e l a t e d w i t h p e r c e n t l a c t o s e ( .37), y i e l d o f m i l k (.25) and w i t h p e r c e n t e n e r g y as p r o t e i n (.33). The f a t p r o t e i n r a t i o was p o s i t i v e l y c o r r e l a t e d w i t h p e r c e n t f a t (.86) and w i t h p e r c e n t e n e r g y as f a t (.94) b u t was n e g a t i v e l y c o r r e l a t e d w i t h p e r c e n t e n e r g y as p r o t e i n (-.93) and p e r c e n t e n e r g y as l a c t o s e ( -.64). CONCLUSIONS AND SUMMARY The H o l s t e i n - A y r s h i r e c r o s s b r e d s a t O y s t e r R i v e r p r o d u c e d s l i g h t l y , b u t n o t s i g n i f i c a n t l y , l e s s m i l k p e r l a c t a t i o n t h a n t h e h i g h e r y i e l d i n g p a r e n t a l b r e e d , t h e H o l s t e i n s , and s i g n i f i c a n t l y more (2 615 p o u n d s ) t h a n t h e l o w e r y i e l d i n g p a r e n t a l b r e e d , t h e A y r s h i r e s . The p e r c e n t a g e o f m i l k f a t and p r o t e i n i n t h e m i l k o f t h e c r o s s b r e d s was a p p r o x i m a t e l y mid-way between t h a t o f t h e two p a r e n t a l b r e e d s . D i f f e r e n c e s i n l a c t a t i o n y i e l d s o f m i l k f a t and p r o t e i n between c r o s s b r e d s and H o l s t e i n s were v e r y s m a l l ; s e v e n pounds o f m i l k f a t i n f a v o u r o f t h e c r o s s b r e d s , and one pound o f p r o t e i n i n f a v o u r o f t h e H o l s t e i n s . T hus t h i s c r o s s b r e d g r o u p was a b l e t o e q u a l t h e p r o d u c t i o n o f t h e h i g h e r y i e l d i n g p a r e n t a l b r e e d i n pounds o f m i l k , m i l k f a t , p r o t e i n and i n m e g a - c a l o r i e s o f e n e r g y p e r l a c t a t i o n . T h i s r e s u l t a g r e e s w i t h r e p o r t s ( 1 8 , 27, 31, 33) i n t h e l i t e r a t u r e t h a t c r o s s b r e d s i n w h i c h one o f t h e p a r e n t a l b r e e d i s H o l s t e i n , f r e q u e n t l y e q u a l b u t s e l d o m s u r p a s s t h e y i e l d s o f t h e H o l s t e i n s . S t a t i s t i c a l a n a l y s i s o f t h e b r e e d by s e a s o n i n t e r - a c t i o n f o r l a c t a t i o n a v e r a g e m i l k f a t p e r c e n t a g e i n d i c a t e d t h a t ; 1) summer and autumn f r e s h e n i n g A y r s h i r e s and c r o s s - b r e d s were n o t s i g n i f i c a n t l y d i f f e r e n t b u t t h e s e two g r o u p s were s i g n i f i c a n t l y h i g h e r t e s t i n g t h a n H o l s t e i n s f r e s h e n i n g a t t h i s t i m e o f y e a r ; 2) w i n t e r and s p r i n g c a l v i n g c r o s s b r e d s were n o t s i g n i f i c a n t l y d i f f e r e n t f r o m w i n t e r and s p r i n g c a l v i n g H o l s t e i n s b u t t h e s e two b r e e d g r o u p s were s i g n i f i c a n t l y l o w e r i n l a c t a t i o n a l a v e r a g e m i l k f a t c o n t e n t t h a n t h e A y r s h i r e s c a l v i n g a t t h i s t i m e o f y e a r . B e c a u s e m i l k f a t i s t h e m a j o r e n e r g y component o f m i l k , i t f o l l o w s t h a t t h e s i g n i f i c a n t b r e e d by s e a s o n i n t e r a c t i o n s t h a t were a p p a r e n t i n t h e e n e r g y r e l a t i o n s h i p s among t h e m a j o r m i l k components c a n be a t t r i b u t e d , a t l e a s t i n p a r t , t o t h e b r e e d by s e a s o n i n t e r a c t i o n s i n l a c t a t i o n a v e r a g e m i l k f a t p e r c e n - t a g e . I f t h i s a p p a r e n t g e n o t y p e - e n v i r o n m e n t i n t e r a c t i o n i s a g e n e r a l phenomena i n d a i r y c a t t l e , t h e n c a r e s h o u l d be t a k e n i n c h o o s i n g a p p r o p r i a t e m a t u r e e q u i v a l e n t c o r r e c t i o n f a c t o r s f o r t h e c a l c u l a t i o n o f m a t u r e e q u i v a l e n t r e c o r d s f o r c r o s s - b r e d c a t t l e : and b r e e d s h o u l d be t a k e n i n t o a c c o u n t i n a d j u s t i n g c a l v i n g d i s t r i b u t i o n s i n m i x e d h e r d s . The d i v i s i o n o f e n e r g y among t h e t h r e e m a j o r m i l k components i n d i c a t e d t h a t : s l i g h t l y l e s s t h a n o n e - h a l f t h e t o t a l m i l k e n e r g y was i n t h e m i l k f a t and t h e r e m a i n d e r o f t h e m i l k e n e r g y was d i v i d e d a l m o s t e q u a l l y between p r o t e i n and l a c t o s e . The t h r e e b r e e d g r o u p s d i d n o t d i f f e r s i g n i f i c a n t l y i n p e r c e n t a g e o f m i l k e n e r g y as p r o t e i n . The o v e r a l l mean was 2 7.5 + .11 p e r c e n t , o r e x p r e s s e d i n t e r m s o f m i l k e n e r g y p e r p ound o f p r o t e i n t h e v a l u e was 9.6 9 + .0 38 m e g a c a l o r i e s p e r p ound o f p r o t e i n . The t h r e e b r e e d g r o u p s d i d d i f f e r s i g n i f i c a n t l y i n t h e p r o p o r t i o n o f t h e t o t a l m i l k e n e r g y a c c o u n t e d f o r by b o t h m i l k f a t and l a c t o s e . The r e s u l t s were t h a t t h e b r e e d w i t h t h e h i g h e s t m i l k f a t t e s t , A y r s h i r e s , h a d a h i g h e r p r o p o r t i o n o f t o t a l m i l k e n e r g y i n t h e m i l k f a t and a l o w e r p r o p o r t i o n i n l a c t o s e t h a n t h e b r e e d w i t h t h e l o w e s t m i l k f a t t e s t — H o l s t e i n s . The t h r e e b r e e d g r o u p s i n c l u d e d i n t h i s s t u d y d i f f e r e d s i g n i f i c a n t l y i n t h e r a t i o o f m i l k f a t t o p r o t e i n . The A y r s h i r e b r e e d had a s i g n i f i c a n t l y w i d e r r a t i o t h a n t h e c r o s s b r e d s and H o l s t e i n s . B r e e d d i f f e r e n c e s i n m i l k f a t t o p r o t e i n r e l a t i o n s h i p s were shown by Overman (30) who f o u n d t h a t r e g r e s s i o n e q u a t i o n s p r e d i c t i n g p r o t e i n p e r c e n t a g e s f r o m m i l k f a t p e r c e n t a g e were d i f f e r e n t f o r e a c h b r e e d . The r e s u l t t h a t p r o t e i n t o e n e r g y r e l a t i o n s h i p s d i d n o t d i f f e r s i g n i f i c a n t l y among t h e t h r e e b r e e d s , w h i l e t h e r e l a t i o n s h i p o f m i l k f a t t o p r o t e i n d i d , w o u l d i n d i c a t e t h a t c a u t i o n s h o u l d be u s e d i n i n t e r p r e t i n g f a t t o p r o t e i n r a t i o s as i n d i c a t o r s o f e n e r g y t o p r o t e i n r e l a t i o n s h i p s f o r between b r e e d c o m p a r i - s o n s , i f t h e r e s u l t s i n t h i s s t u d y a r e g e n e r a l l y t r u e . S e a s o n o f f r e s h e n i n g d i d n o t a c c o u n t f o r a s i g n i f i c a n t p o r t i o n o f v a r i a t i o n i n any o f t h e y i e l d t r a i t s u n d e r s t u d y . However, t h e t r e n d was f o r f a l l a n d w i n t e r f r e s h e n i n g cows t o h a v e h i g h e r y i e l d s t h a n cows f r e s h e n i n g i n t h e s p r i n g and e a r l y summer. S e a s o n o f f r e s h e n i n g was a s i g n i f i c a n t s o u r c e o f v a r i a t i o n f o r p e r c e n t m i l k f a t , f o r p e r c e n t t o t a l o r g a n i c s o l i d s and f o r p e r f o r m a n c e t r a i t s i n v o l v i n g e n e r g y r e l a t i o n - s h i p s . However, y e a r by s e a s o n i n t e r a c t i o n s were a l s o s i g n i f i c a n t s o u r c e s o f v a r i a t i o n f o r t h e s e t r a i t s . The m a i n r e a s o n f o r t h i s s i g n i f i c a n t y e a r by s e a s o n i n t e r a c t i o n was t h a t cows t h a t c a l v e d f r o m December t o March i n c l u s i v e i n t h e f i r s t y e a r o f t h e s t u d y were w e l l b e l o w t h e o v e r a l l a v e r a g e f o r l a c t a t i o n a l a v e r a g e m i l k f a t p e r c e n t a g e , w h i l e t h o s e t h a t c a l v e d d u r i n g t h i s p e r i o d i n t h e s e c o n d y e a r were a b o v e t h e o v e r a l l a v e r a g e . As management i n b o t h y e a r s was e s s e n t i a l l y t h e same, t h e r e a s o n f o r t h e d i f f e r e n t i a l s e a s o n r e s p o n s e by y e a r i s n o t r e a d i l y a p p a r e n t b u t may be due t o d i f f e r e n c e s i n w e a t h e r c o n d i t i o n s . 93 . LITERATURE CITED 1. A l e x a n d e r , W.H. and F.B. L e e c h , 1959. A q u a n t i t a t i v e e v a l u a t i o n o f some f a c t o r s a f f e c t i n g t h e n o n - f a t t y s o l i d s o f cows m i l k . J . D a i r y Res. 27: 19-32. 2. B a i l e y , G.L., 1952. S t u d i e s i n l a c t a t i o n y i e l d i n t h e s o l i d s - n o t - f a t c o n t e n t o f m i l k . I . V a r i a t i o n i n l a c t a t i o n y i e l d , m i l k - f a t p e r c e n t a g e and s o l i d s - n o t - f a t p e r c e n t , t h a t a r e due t o t h e age o f t h e cow. J . D a i r y Res. 19: 89-100. 3. B a i l e y , G.L., 1952. S t u d i e s i n l a c t a t i o n y i e l d i n t h e s o l i d s - n o t - f a t c o n t e n t o f m i l k . I I . V a r i a t i o n due t o s t a g e i n l a c t a t i o n . J . D a i r y Res. 19: 102-108. 4. B a i l e y , G.L., 1952. S t u d i e s i n l a c t a t i o n y i e l d i n t h e s o l i d s - n o t - f a t c o n t e n t o f m i l k . I I I . S e a s o n a l v a r i a t i o n . J . D a i r y Res. 19: 109-114. 5. B e r r y , J . C . , 1967. T e s t f o r b u t t e r f a t — But s e l e c t a g a i n s t i t . H o l s t e i n - F r i e s i a n J o u r . 3 0 ( 2 ) : 23. 6. B e r e s k i n , B. and R.W. T o u c h b e r r y , 1966. C r o s s b r e e d i n g d a i r y c a t t l e . I I I . F i r s t l a c t a t i o n p r o d u c t i o n . J . D a i r y S c i . 49: 659-667. 7. B i g g s , D.A., 1967. M i l k a n a l y s i s w i t h t h e i n f r a r e d m i l k a n a l y z e r . J . D a i r y S c i . 50: 799-803. 8. B l a n c h a r d , R.P., A.E. Freeman and P.W. S p i k e , 1966. V a r i a t i o n i n l a c t a t i o n y i e l d o f m i l k c o n s t i t u e n t s . J . D a i r y S c i . 49: 953-956. 9. B r a n d t , G.W., C C . B r a n n o n , W.R. H a r v e y and R.E. M c D o w e l l , 1966. E f f e c t o f c r o s s b r e e d i n g on p r o d u c t i o n t r a i t s i n d a i r y c a t t l e . J . D a i r y S c i . 4 9 1249-1253. 10. B u t c h e r , K.R., F.D. S a r g e n t and J . E . L e g a t e s , 1967. E s t i m a t i o n o f g e n e t i c p a r a m e t e r s f o r m i l k c o n s t i t u e n t s . J . D a i r y S c i . 50: 185-193. 11. C h r i s t e n s e n , L. and F.R. J o h n s o n , 1967. E x p e r i e n c e s w i t h s o l i d - n o t - f a t and p r o t e i n t e s t i n g . J . D a i r y S c i . 50: 796-798. 12. E i s e n , E . J . , 1967. E f f e c t o f t h e b i o m e t r i c a l r e l a t i o n - s h i p among t o t a l m i l k y i e l d , m i l k c o n s t i t u e n t y i e l d , and p e r c e n t o f m i l k c o n s t i t u e n t on r e s p o n s e t o s e l e c t i o n . J . D a i r y S c i . 49: 1230-1234. 94. 13. E r b s , R.E., 1960. What's i n i t f o r p r o d u c e r s and t h e i n d u s t r y t o p r i c e m i l k on a c o m p o s i t i o n b a s i s ? T h i r d ADA N a t l . Symposium D a i r y M a r k e t D e v e l o p - ment, p. 41. 14. F o s g a t e , O.T. and H.K. W e l c h , 1960. E f f e c t o f c e r t a i n e n v i r o n m e n t a l f a c t o r s upon m i l k p r o d u c t i o n i n G e o r g i a . A b s t r . J . D a i r y S c i . 43: 442. 15. G a c u l a , M.C. J r . , S.W. G a u n t , and R.A. Damon J r . , 1968. G e n e t i c and e n v i r o n m e n t a l p a r a m e t e r s o f m i l k c o n - s t i t u e n t s f o r f i v e b r e e d s . I . E f f e c t s o f y , h e r d , y e a r , s e a s o n and age o f t h e cow. J . D a i r y S c i . 51: 428-437. 16. H a r v e y , W.R., 1960. L e a s t s q u a r e s a n a l y s i s o f d a t a w i t h u n e q u a l s u b c l a s s numbers. ARS-20-8 USDA, B e l t s v i l l e , M a r y l a n d . 17. J e n n e s s , R. and S. P a t t o n , 1959. P r i n c i p l e s o f d a i r y c h e m i s t r y . J o h n W i l e y a n d S o n s , New Y o r k , p . 22. 18. J o h n s o n , J . C . J r . , R.D. J o h n s o n , W.R. H a r v e y , R.E. M c D o w e l l and B.L. S o u t h w e l l , 1964. P e r f o r m a n c e o f c r o s s b r e d and p u r e b r e d d a i r y c a t t l e . A b s t r . J . A n i m a l S c i . 28: 850. 19. J o h n s t o n e , J . E . , C. L e w i s , E . J . S t o n e a n d C. B r a n t o n , 1956. The i n f l u e n c e o f s e a s o n o f f r e s h e n i n g on p r o d u c t i o n r e c o r d s o f J e r s e y and H o l s t e i n cows i n L o u i s i a n a . A b s t r . J . D a i r y S c i . 39: 933. 20. K i d d y , A.C., 1963. Methods f o r s o l i d s - n o t - f a t a n d p r o t e i n d e t e r m i n a t i o n . J . D a i r y S c i . 46: 1289-1293. 21. K r a m e r , C.L., 1957. E x t e n s i o n o f m u l t i p l e r a n g e t e s t s t o g r o u p c o r r e l a t e d a d j u s t e d means. B i o m e t r i c s 13: 13-18. 22. L a b e n , R.C., 1963. F a c t o r s r e s p o n s i b l e f o r v a r i a t i o n i n m i l k c o m p o s i t i o n . J . D a i r y S c i . 46: 1293- 1301. 23. L e B e r o n , A. and R. B r o g , 1968. A c c o u n t i n g f o r p r o t e i n i n d a i r y m a n u f a c t u r i n g p r o c e s s e s . J . D a i r y S c i . 51: 1980-1985. 24. L e e , J . E . , O.T. F o s g a t e and J . L . Carman, 1961. Some e f f e c t s o f c e r t a i n e n v i r o n m e n t a l and i n h e r i t e d i n f l u e n c e s upon m i l k and f a t p r o d u c t i o n i n d a i r y c a t t l e . J . D a i r y S c i . 44: 296-299. 9 5 . 25. L e g a t e s , J . E . , 1960. G e n e t i c and e n v i r o n m e n t a l f a c t o r s a f f e c t i n g t h e s o l i d s - n o t - f a t components o f m i l k . J . D a i r y S c i . 43: 1527-1532. 26. L o g a n a t h a n , S. and N.R. Thompson, 1968. C o m p o s i t i o n o f cows m i l k . I . E n v i r o n m e n t a l and m a n a g e r i a l i n f l u e n c e s . J . D a i r y S c i . 51: 1928-1932. 27. M c D o w e l l , R.E. and B.T. M c D a n i e l , 1968. I n t e r b r e e d m a t i n g s i n d a i r y c a t t l e . I . Y i e l d t r a i t s , f e e d e f f i c i e n c y , . t y p e s and r a t e o f m i l k i n g . J . D a i r y S c i . 51: 767-777. 28. M c D o w e l l , R.E. and B.T. M c D a n i e l , 1968. I n t e r b r e e d m a t i n g s i n d a i r y c a t t l e . I I I . E c o n o m i c a s p e c t s . J . D a i r y S c i . 51: 1649-1658. 29. O l o u f a , M.M. and I.R. J o n e s , 1948. The r e l a t i o n b etween month o f c a l v i n g and y e a r l y b u t t e r f a t p r o d u c t i o n . J . D a i r y S c i . 31: 1029-1031. 30. Overman, O.R., O.F. G a r r e t t , K.E. W r i g h t , and F.P. Sanmann, 19 39. C o m p o s i t i o n o f m i l k o f Brown S w i s s cows. 111. A g r . E x p . S t a . B u l l . 45 7. 31. P e a r s o n , L. and R.E. M c D o w e l l , 19 68. C r o s s b r e e d i n g o f d a i r y c a t t l e i n t e m p e r a t e z o n e s . A r e v i e w o f r e c e n t s t u d i e s . Anim. B r e e d . A b s t r . 36: 1-15. 32. R o b e r t s o n , A., R. W a i t e , and J.C.D. W h i t e , 1956. V a r i a t i o n i n t h e c h e m i c a l c o m p o s i t i o n o f m i l k w i t h p a r t i c u l a r r e f e r e n c e t o t h e s o l i d s - n o t - f a t . I I . E f f e c t s o f h e r e d i t a r y . J . D a i r y Res. 23: 82-91. 33. R o b e r t s o n , A., 1949. C r o s s b r e e d i n g e x p e r i m e n t s w i t h d a i r y c a t t l e . Anim. B r e e d . A b s t r . 17: 201-208. 34. S a r g e n t , F.D., K.R. B u t c h e r and J . E . L e g a t e s , 1967. E n v i r o n m e n t a l i n f l u e n c e s on m i l k c o n s t i t u e n t s . J . D a i r y S c i . 50: 177-184. 35. S a r g e n t , F.D., V.H. L y t t o n and O.G. W a l l , J r . , 196 8. T e s t i n t e r v a l method o f c a l c u l a t i n g d a i r y h e r d i mprovement a s s o c i a t i o n r e c o r d s . J . D a i r y S c i . 51: 170-179. 36. S t a r k e y , E . E . , E . L . C o r b y and E . E . H i e z e r , 1958. E f f e c t o f c e r t a i n m e a s u r e d e n v i r o n m e n t a l i n f l u e n c e s on t h e b u t t e r f a t y i e l d o f H o l s t e i n - F r i e s i a n c a t t l e . A b s t r . J . D a i r y S c i . 41: 722. 96. 37. Thompson, N.R. and S. L o g a n a t h a n , 1968. C o m p o s i t i o n o f cows m i l k . I I . G e n e t i c i n f l u e n c e s . J . D a i r y S c i . 51: 1933-1935. 38. W a i t e , R., J.C.D. W h i t e and A. R o b e r t s o n , 1956. V a r i a t i o n i n t h e c h e m i c a l c o m p o s i t i o n o f m i l k w i t h p a r t i c u l a r r e f e r e n c e t o t h e s o l i d s - n o t - f a t . I . The e f f e c t o f s t a g e o f l a c t a t i o n , s e a s o n o f y e a r and age o f t h e cow. J . D a i r y Res. 23: 65-81. 39. Wood, P.D.P., 1970. The r e l a t i o n s h i p b etween month o f c a l v i n g and m i l k p r o d u c t i o n . Anim. P r o d . 12: 253-259. 40. Woodward, T . E . , 1945. Some s t u d i e s o f l a c t a t i o n r e c o r d s . J . D a i r y S c i . 28: 209-218.

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