"Land and Food Systems, Faculty of"@en . "DSpace"@en . "UBCV"@en . "Williams, Christopher John"@en . "2011-05-06T00:26:06Z"@en . "1971"@en . "Master of Science - MSc"@en . "University of British Columbia"@en . "A total of 238 records (101 Holstein, 63 Ayrshire and 74 crossbred) made by cows calving in a two year period from August 1967 to July 1969 inclusive at the Oyster River Research Farm were used to study: a) lactation yields of; milk, milk fat, protein, lactose, total organic solids, and energy; b) lactation average percent; milk fat, protein lactose and total organic solids; c) percent milk energy as; milk fat, protein and lactose; d) the ratio of fat production to protein production, and e) the energy concentration of the milk.\r\nStatistical analyses were by the least squares method of Harvey (16). Constants were fitted for the three breed groups, for the two years included in this study and for the season of lactation start. Constants were also fitted for all interactions. Number of days milked, age in days of the cow at parturition, and number of days open were used as co-variables. A significance level of 5 percent was used throughout.\r\nBreed group and the co-variables of days milked and age were significant for yield traits. The Holsteins and crossbreds did not differ significantly from each other but both groups had significantly higher yields than the Ayrshires. The least squares overall means for yields of; milk, milk fat, protein, lactose, total organic solids and energy were; 14,914 \u00B1 177, 548 \u00B1 7.3, 510.9 \u00B1 6.1, 738.4 \u00B1 9.2, 1,797.6 \u00B1 21.2 lbs., and 4,946 \u00B1 58.9 mcal respectively. The least squares constants for each breed for the above listed traits (in the same order) were: 1) Holstein; 1,239 \u00B1 244, 14.2 \u00B1 10.0, 27.2 \u00B1 8.4 60.2 \u00B1 12.7 lbs., and 238.6 \u00B1 81.2 mcal; 2) crossbred 688 \u00B1 240, 21.6 \u00B1 9.9, 26.2 \u00B1 8.2, 37.2 \u00B1 12.5 lbs., and 225.6 \u00B1 80.1 mcals; and 3) Ayrshire; -1927 \u00B1 256, -35.8 \u00B1 10.5, -53.4 \u00B1 8.8, -97 \u00B1 13.3, -186.5 \u00B1 30.7 lbs., and -464 \u00B1 85.1 mcals.\r\nThe partial regression coefficients of all yield traits on number of days milked and on age at parturition were significant and positive.\r\nThe overall least squares mean percent protein was 3.44 \u00B1 0.015. The breed least squares constants for Holstein, crossbred and Ayrshire were; -0.11 \u00B1 0.021, ).02 \u00B1 0.021, and 0.09 \u00B1 0.022 respectively. Differences between crossbred and Ayrshire means were non significant but both breed group means were significantly higher than the Holstein.\r\nBreed, season, breed by season and year by season were significant sources of variation for percent milk fat and percent total organic solids. Ayrshire means were higher than Holstein for all seasons. For winter calving, crossbred means did not differ significantly from Holstein; for summer calving, crossbred means did not differ significantly from Ayrshire. Differences among Holstein season means were non significant. Crossbreds and Ayrshires calving in the summer tended to have higher percentages than winter or spring calvers. Means of winter calving cows were higher in the second year than in the first year.\r\nPercent lactose increased from 4.88 \u00B1 0.019 in the first year to 5.02 \u00B1 0.017 in the second year.\r\nSignificant standard partial regression coefficients for days milked were; percent milk fat 0.2 7 \u00B1 0.06, percent lactose 0.2 8 \u00B1 0.06, and percent total organic 0.31 \u00B1 0.06.\r\nBreed, season, breed by season, year by season and days milked were all significant effects on percent milk energy as milk fat, the ratio of milk fat to protein and the energy concentration of the milk. Since percent milk fat is highly correlated with the above traits (correlation coefficients were 0.96, 0.86, and 0.97 respectively) the results were very similar to those obtained for percent milk fat.\r\nSeason, year, breed by season and days milked were significant effects on percent milk energy as protein. Higher values were associated with winter calving than summer calving and the effect of season was greater on crossbred than on the other two breed groups. The standard partial regression coefficient for days milked was -0.2 8 \u00B1 0.07. The means for the first year was 27.8 \u00B1 0.20 and for the second was 27.2\u00B10.25.\r\nBreed, season, year by season and age were significant for percent energy as lactose. Breed means, which were all significantly different from each other were 27.7 \u00B1 0.22, 26.8 \u00B1 0.20 and 25.6 \u00B1 0.24 for Holstein, crossbred and Ayrshire respectively. Higher values were associated with winter calving and differences were greater in the first year than the second year. The standard partial regression coefficient for age was -.20 \u00B1 0.06."@en . "https://circle.library.ubc.ca/rest/handle/2429/34316?expand=metadata"@en . "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,\u00E2\u0080\u00A2 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 \u00E2\u0080\u00A2 3 \u00E2\u0080\u00A2 3 \u00E2\u0080\u00A2 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 \u00C2\u00A3 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 \u00C2\u00BB < to X3 to O m (0 to o o (0 ro in to\" c '5 o MILK o o E CM 0 0 \u00C2\u00A9 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 '\u00C2\u00A9 to o X ENERGY Ls.Sq \u00E2\u0080\u00A2Mean 4,947 cn o o cn O o o m z: m b 2) o o o \u00E2\u0080\u00A2< O J - < \"8 p \u00C2\u00B0 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 \u00E2\u0080\u00A2o \u00C2\u00A9 1. J Q OT V> o co Xi CO ro m c '\u00C2\u00A9 o PROTEIN Ls.Sq. Wean 511. CO CO xz to < to CO Is-Is-\u00E2\u0080\u00A2o \u00C2\u00A9 J Q in co o t> O Ls.Sq. -Mean 738. CO j Q Oi 0) Is-c '\u00C2\u00A9 \u00E2\u0080\u00A24\u00E2\u0080\u0094 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 \u00E2\u0080\u00941 \u00E2\u0080\u00A2 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 \u00E2\u0080\u00A2 S \u00E2\u0080\u00A2 S \u00E2\u0080\u00A2 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 >\u00C2\u00BB < ro 0) i . -O (0 10 o o Ls.Sq. -Mean 3.69% ro c *\u00E2\u0080\u0094 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> \u00E2\u0080\u00A2\u00E2\u0080\u00A2\u00E2\u0080\u0094 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 \u00E2\u0080\u00A2% 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 '- ^\u00E2\u0080\u0094^ 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 \u00E2\u0080\u00A2 -.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 \u00E2\u0080\u0094 -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\u00C2\u00B0 .16 + . l l b Apr - May .21 + .0 8* -.10 + .10 .11 + .09 -.31 + .09 -.29 + .12\u00C2\u00B0 .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\u00C2\u00B0 .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 +\u00E2\u0080\u00A2 .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 O^N DTJ FTM A^M JTJ ATS O^N DTJ F^M A^M J^ 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 . \u00E2\u0080\u00A2 Y e a r - S e a s o n M e a n s A S ea son Cons tan t s \u00E2\u0080\u00A2s O^N DTJ FTM ATM JIJ ATS O^N DTJ F^M A^M J^ 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 \u00E2\u0080\u00A2 5 \u00E2\u0080\u00A2 S \u00E2\u0080\u00A2 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 \u00E2\u0080\u00A2 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 \u00C2\u00AB 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 \u00C2\u00B0 - 0 .030 + 0.011 - 0 . 013 + 0.011 -11 .9 + 2.0 \u00E2\u0080\u00A20.10 + 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 \u00E2\u0080\u00A2o 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 \u00C2\u00BB_ o CO CM 0) +-W O X PROTEIN Ls.Sq. \u00E2\u0080\u00A2Mean 27.4% CO in CM CD to >\u00C2\u00BB < 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 \u00C2\u00B1 . 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\u00C2\u00BB*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 . \u00E2\u0080\u00A2 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 :\u00E2\u0080\u0094 \u00E2\u0080\u0094 \u00E2\u0080\u0094 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 \u00E2\u0080\u00A2 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\u00C2\u00B0 .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 . \u00C2\u00A71 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 . \u00E2\u0080\u009E 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* \u00E2\u0080\u00A2 .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 \u00E2\u0080\u00A2 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 \u00E2\u0080\u0094 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. 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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."@en . "Text"@en . "http://hdl.handle.net/2429/34316"@en .