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Relationships Between Sires and Sons for Evaluations from First, All, and Later Records
Relationships Between Sires and Sons for Evaluations from First, All, and Later Records B. G. CASSELL, K. L. LEE, and G. KROLL Department of Dairy Science Virginia Polytechnic Institute and State University Blacksburg 24061 H. D. N O R M A N Animal Improvement Programs Laboratory Agriculture Research Service United States Department of Agriculture Beltsville, MD 20705 ABSTRACT
INTRODUCTION
January 1984 Modified Contemporary Comparison sire evaluations for first, all, and later records were used to create sire-son pairs in five dairy breeds. Each evaluation for each bull included 10 or more daughters. Regressions of son on sire for evaluations for first, all, or later records exceeded the expectation of .5 and were most divergent for Jerseys and Brown Swiss. Regressions and coefficients of determination were generally highest when sire's evaluation based on all records predicted sons' evaluations from first, all, or later records. Regression of son on sire for difference in evaluations (later minus first) was positive in all breeds, ranging from .08 to .10, and was significant for all breeds except Brown Swiss. Coefficients of determination were low (.01 to .02). Both regression of son on sire for difference and coefficient of determination increased with son's Repeatability, with a regression of .33 and a coefficient of determination of .09 for sons over 99% Repeatability, Regressions for 8,055 Holsteins with evaluations for sires and maternal grandsires on those ancestors were .46 to .54 for sires and .25 t o . 31 for maternal grandsires. Regressions of son's evaluation on pedigree index were .94 for first, 1.05 for all, and 1.12 for later lactations.
The choice of lactations to include in sire evaluations recently has been reviewed (4). Later lactations are important to the economic health of the dairy herd as they occur with greater frequency and at higher yields than first records. Computationally, such records are difficult to include in sire evaluation and are subject to culling bias (7, 8, 9, 10, 11, 12) unless proper models are used. However, later records increase the accuracy of evaluations (5, 6, 15, 20) through additional information and more ties among sires. Further, they have been shown (3, 5, 19) to affect sire rank with important variation from sire to sire in difference between evaluations based on first and later records. The importance o f later records to accurate sire rankings suggests that relationships among sires, MGS, and sons should be examined for evaluations based on first, all, and later records. Such relationships have been examined for all lactation evaluations by Powell et al. (12) for all breeds. These workers found a regression of near 1.0 for average Modified Contemporary Deviation on pedigree index (PI). Rothschild et al. (13) reported correlations between son and sire near expectation for Modified Contemporary Comparison (MCC) sire evaluations. Vinson and White (17) regressed son MCC evaluations from all lactations on sire and MGS evaluations (by approximate MCC methods) from first records. Results varied b y type of sampling [artificial insemination (AI) or not] but were consistently less than expectation (.26 to .41 for sires and .11 to .17 for MGS). Whether use of different records in evaluations of sires, and sons accounted for differences from expected values is not known. Differences in sire evalua-
Received April 25, I985. 1985 J Dairy Sci 68:3291-3300
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tion methodology could be involved. Schaeffer's (14) work with first lactation Canadian evaluations yielded partial regression coefficients of .497 for sires and .243 for MGS; results were very near the expected .5 and .25. The difference in evaluations from first and later records has implications for net present value of semen from different bulls (18). Such differences could be important, if they proved transmittable, in selecting sires of sons. Bar-Anan et al. (1), using Israeli sire evaluations from first, second, third, and pooled lactations, reported a regression coefficient of .49 for son on sire for change from first to second evaluation. Variation of sons within sire was large. No such estimates exist for MCC evaluations. The purpose of this study was to examine the regression of son on sire for evaluations based on different parities for five major dairy breeds. The utility of pedigree evaluations from first, all, and later records was of interest. The study also was to determine if the differences in rate of maturity apparent in previous studies had a genetic basis or were simply a function of unaccounted environmental sources of variation or biases due to female culling. MATERIALS AND METHODS
Data were all sire evaluations for milk in Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss breeds from the January 1984 MCC. Published evaluations utilize all lactations. However, separate evaluations from first records and later records are routinely calculated in the MCC and were used in the study. Each evaluation included at least 10 daughters. Each bull's record contained sire and MGS identification. Two hundred sixty-two Ayrshire, 1,130 Guernsey, 17,882 Holstein, 3,920 Jersey, and 475 Brown Swiss sire-son pairs in which sires and sons had genetic evaluations were created. Sire records were repeated for each son in the data. Holstein records were further divided to include a group of 3,920 sire-son pairs in which the son entered AI service prior to 40 mo of age. Regressions of son on sire were calculated for all nine combinations of first, all, and later lactation evaluations for sires and sons in each breed. In Holsteins, a further match on MGS produced 8,055 records with evaluations from first, all, and later records on sons, sires, and
Journal of Dairy Science Vol. 68, No. 12, 1985
MGS. From these records, PI was calculated as PI -- .5 (sire PDM), + .25 (MGS PDM) where PDM is Predicted Difference Milk. January 1984 MCC used the PD 82 genetic base and the "ancestor merit" method (21) of incorporating pedigree information into sire evaluations. RESULTS A N D DISCUSSION
Means of evaluations and their Repeatabilities for sires and sons in each breed are in Table 1. Average evaluations for sires exceeded those for sons in most cases. Average differences (later minus first evaluation) were positive for sons but negative for sires in all breeds except Brown Swiss. Cassell et al. (3) reported differences of 36, 0, 6, 35, and 35 kg for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss sires using these same data. Negative differences for sires could be due to inclusion of higher percentages of terminal records in their later evaluations. Cassell et al. (6) reported a larger positive difference for 200 widely used Holstein sires when later records were restricted to second lactations only compared to all later records. That study and the current study suggest that terminal records depress later lactation evaluations relative to first lactation evaluations. Differences in genetic trend from first and later records could also be involved. Cassell et al. (3, 5) reported negative correlations ( - . 1 8 to - . 2 5 ) between sire's age and difference in evaluations. Average Repeatabilities indicated that most sons were not used in AI whereas most sires were. Average Repeatabilities were always highest for all lactation evaluations, as expected, since first and later evaluations are subsets. Repeatabilities for later evaluation were almost always higher than for first evaluations, although such differences would be expected to be minor, because for most sires, additional data in later evaluations would be from additional records on the same daughters. Standard deviations of evaluations and Repeatabilities are in Table 2. In all breeds except AI Holsteins, sire evaluations were more variable than son evaluations. This result is expected from selection index theory and results from the low average Repeatability of son evaluations and their subsequent regression toward pedigree predictions. For A1 Holsteins, sons' evaluations were not regressed as heavily
TABLE 1. Means of evaluations based on different lactations for sires and sons. Holstein
O
Number of pairs Predicted Difference milk, kg First lactations Son Sire All lactations Son Sire Later lactations Son Sire Difference 2 Son Sire Repeatabilities First lactations Son Sire All lactations Son Sire Later lactations Son Sire
Ayrshire
Guernsey
All
AI 1
Jersey
Brown Swiss
262
1,130
17,882
3,920
1,509
475
-239 -155
-295 -234
-342 --151
-174 57
-294 -199
--342 --337
-222 -176
-290 -269
--331 --190
-148 6
-272 -213
--332 --341
-232 -180
-280 -280
--316 -212
-118 -27
-245 -201
--329 --318
5 -25
15 -46
26 --61
56 -84
50 -2
14 19
O
Fo O0
Z
.34 .74
.32 .79
.37 .92
.67 .98
.35 .82
.34 .73
.42 .80
.37 .83
.44 .94
.74 .99
.41 .86
.42 .79
.38 .78
.33 .81
.39 .93
.66 .99
.37 .84
.38 .77
O
Z
0 Z
>
< Ox O0
t~
1 Sons entering artificial insemination (AI) prior to 40 mo of age. z Later lactation evaluation minus first lactation evaluation.
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TABLE 2. Standard deviations of evaluations based on different lactations for sires and sons. Holstein
Predicted Difference milk, kg First lactations Son Sire All lactations Son Sire Later lactations Son Sire Difference 2 Son Sire Repeatabilities First lactations Son
Sire All lactations Son Sire Later lactations Son Sire
Ayrshire
Guernsey
All
AIl
Jersey
Brown Swiss
215 280
173 201
262 357
263 255
239 289
273 305
216 258
187 202
273 335
269 243
247 278
267 292
199 241
185 203
276 325
268 246
241 268
229 269
118 113
99 102
143 143
176 134
93 82
139 125
•18 •28
.16 .27
.21 .19
.16 .06
.19 .25
.18 .27
.19 .24
.17 .24
.22 .17
.14 .05
.20 .22
.19 .24
.18
.16
.20
.17
.18
.17
•2 5
.25
.18
.05
.23
.25
Sons entering artificial insemination (AI) prior to 40 mo of age. 2 Later lactation evaluation minus first lactation evaluation. and sires were m o r e carefully selected as evidenced by the higher means in Table 1. In m o s t breeds, sire evaluations f r o m first records were m o r e variable than evaluations f r o m all or later records. First evaluations were m o r e variable for sons in Brown Swiss. Average differences b e t w e e n evaluations f r o m first, all, and later records are d e t e r m i n e d by the genetic bases established for each breed and evaluation. Standard deviations of difference reflect variation f r o m sire to sire in such differences. This variation could be of e c o n o m i c importance. Cassell et al. (3) r e p o r t e d standard deviations o f difference of 114, 94, 142, 91, and 134 kg for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss f r o m these data. Only Holstein AI sons deviated greatly f r o m these standard deviations. S o m e o f these sons could still be adding daughter i n f o r m a t i o n to their evaluations, a situation that could give rise to sample differences b e t w e e n first and later evaluations. Standard deviations o f Repeatabilities were greater for sires than sons e x c e p t for AI HolJournal of Dairy Science Vol. 68, No. 12, 1985
steins, where high Repeatability sires pred o m i n a t e d . Low standard deviations of son Repeatabilities and low averages in Table 1 indicate that m o s t sons in the data were used only in natural service. Regressions o f son evaluations on sire evaluations are in Table 3. For pairs of evaluations based on the same record groups, the e x p e c t a t i o n of these regressions is .5 (16). Vinson (16) cautioned that empirical regressions could be influenced substantially by part-whole relationships (sire's evaluation in ancester m e r i t p o r t i o n o f MCC) when son's Repeatability was "small". Further, the e x p e c t a t i o n is based on the assumption that genetic merit of MGS is u n c o r r e l a t e d with genetic merit of sires of sons. The validity of such an assumption may be questionable across the years represented in these data. Where record groups differ, such as regression of son's first evaluation on sire's later evaluation, the e x p e c t a t i o n includes terms involving genetic correlation among first and second, third, or subsequent records and w o u l d be less than .5. Because we had no knowledge
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TABLE 3. Regression (b) and coefficient of determination (R 2) of son on sire for milk evaluations based on different lactations.1,2 Lactations used in sire's evaluation Lactations used in sons's evaluations Ayrshire First All Later
Guernsey First All Later Holstein, All First All Later
Holstein, AI 3 First All Later Jersey First All Later Brown Swiss First
All Later
First
All
Later
b
R2
b
R=
b
R2
.56 .54 .49
.52 .49 .47
.63 .62 .56
.56 .54 .53
.65 .65 .60
.54 .53 .52
.60 .64 .64
.48 .47 .49
.62 .67 .68
.53 .53 .55
.60 .66 .67
.50 .51 .54
.52 .54 .55
.50 .49 .51
.57 .59 .61
.53 .53 .55
.58 .61 .63
.51 .52 .55
.50 .50 .51
.23 .22 .23
.53 .56 .59
.24 .25 .29
.50 .54 .58
.22 .24 .29
.65 .66 .65
.61 .59 .61
.68 .70 .70
.63 .62 .64
.70 .72 .72
.62 .61 .64
.63 .62 .54
.50 .51 .51
.67 .66 .57
.52 .52 .53
.71 .70 .61
.50 .49 .51
All regressions significant (P<.05). 2Standard errors of regressions were: Ayrshire, .03 to .04; Guernsey, .02; Holstein (all), .004; Holstein (AI), .01 to .02; Jersey, .01 ; and Brown Swiss, .02 to .03. 3 Sons entering artificial insemination (AI) prior to 40 mo of age.
o f t h e p r o p o r t i o n o f s e c o n d , third, a n d subseq u e n t r e c o r d s in each b u l l ' s e v a l u a t i o n s , n o a t t e m p t was m a d e t o derive a precise e x p e c t a t i o n . Finally, r e l a t i o n s h i p s b e t w e e n first or later a n d all l a c t a t i o n e v a l u a t i o n s are p a r t - w h o l e in n a t u r e , as s o m e c o m m o n r e c o r d s w o u l d a p p e a r in b o t h e v a l u a t i o n s . All regressions e x c e p t s o n ' s later o n sire's first e v a l u a t i o n s in A y r s h i r e s were a b o v e .5. Powell et al. (12) f o u n d regressions c e n t e r e d o n e x p e c t a t i o n s while t h o s e o f V i n s o n a n d White ( 1 7 ) were c o n s i s t e n t l y less t h a n e x p e c t e d . T h e g r e a t e s t d i f f e r e n c e s a b o v e e x p e c t e d values in t h e p r e s e n t s t u d y were for Jerseys, as previously o b s e r v e d (2, 12). O n e r e a s o n f o r regression o f s o n o n sire to e x c e e d e x p e c t a t i o n w o u l d b e positive c o v a r i a n c e s b e t w e e n evaluat i o n s o f sires a n d MGS. If such a c o v a r i a n c e
existed, regression o f s o n ' s PD o n sire a n d M G S s i m u l t a n e o u s l y s h o u l d p r o d u c e regression closer t o e x p e c t e d .5 a n d .25. T a b l e 7 s h o w s t h e results o f such a m o d e l for 8 , 0 5 5 H o l s t e i n bulls w i t h e v a l u a t i o n s o n sire a n d m a t e r n a l grandsire. Results are closer t o e x p e c t e d values t h a n t h o s e in T a b l e 3 f o r all a n d l a t e r l a c t a t i o n e v a l u a t i o n s . Regressions using first l a c t a t i o n e v a l u a t i o n s o f sires were c o n s i s t e n t l y l o w e r t h a n t h o s e using e v a l u a t i o n s f r o m all or l a t e r r e c o r d s o f sires. Such c o m p a r i s o n s c a n b e i n f l u e n c e d b y t h e v a r i a t i o n in t h e e v a l u a t i o n s o f sires if c o v a r i a n c e b e t w e e n sires a n d sons are stable. S t a n d a r d i z e d regression c o e f f i c i e n t s w e r e m u c h m o r e similar across r e c o r d sets u s e d in sire e v a l u a t i o n s t h a n t h o s e in T a b l e 3 b u t w e r e c o n s i s t e n t l y l o w e r f o r first l a c t a t i o n e v a l u a t i o n s o f sires. C o e f f i c i e n t s o f d e t e r m i n a t i o n (R 2) Journal of Dairy Science Vol. 68, No. 12, 1985
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indicate the accuracy with which son's performance can be predicted by sire's evaluations. The R z from using sire evaluations from all lactations exceeded those from first in all cases and those from later in 15 of 18 cases. This was the expected result because of the additional data in all lactation evaluations and the partwhole nature of the relationships. Evaluations for sons are partly determined by sire and maternal grandsire genetic merit (21). All lactation evaluations for sires and maternal grandsires are used for this purpose, regardless of the records involved in sons' evaluations. The R 2 for the AI Holstein subset were considerably lower than other results in Table 3. Holstein AI sons had higher Repeatabilities than other Holstein sons and their evaluations were less affected by the PD of their sire through the ancestor merit portion of the PD equation. As more daughter information becomes available on sons, their evaluations will deviate from pedigree predictions. The net effect is a lowering of R z with little effect on the regression coefficients. Table 2 also shows lower standard deviations of evaluations for sires of AI sons, which is evidence that these sires were more carefully selected than sires of all sons. Such selection will bias downward correlation between sires and sons, thus reducing R 2' A major objective of the study was to determine the relationship between differences in first and later lactation evaluations for sires and sons. Differences in first and later lactation evaluations reflect differences in rate of maturity of daughters. Results are in Table 4. Regressions were positive in all breeds and significantly greater than zero except for Brown Swiss. Tendencies for a sire's daughters to produce more (or less) in later lactations than they did in first lactations were transmittable to daughters of a son. Our ability to predict differences for individual bulls was poor as shown by low R 2. Difference between first and later lactation evaluations can be affected by the sample of daughters in each evaluation, by the age of daughters involved, by the presence of terminal records, and by differences in rate of maturity. Thus, low R 2 are not surprising for the average Repeatabilities (.34 to .44) of sons involved in this study. Both regressions and R 2 increased for AI Holsteins for difference in later and first Journal of Dairy Science Vol. 68, No. 12, 1985
evaluations. To examine the extent of this trend, Table 5 was created by limiting the Holstein data to sires over 90% Repeatability for all lactations and subsetting sons on the basis of all lactation Repeatability. The regression of son on sire for difference increased from .02 for sons with Repeatabilities less than 30% to .33 for sons with Repeatabilities above 99%. The R 2 increased from .03 to .09 for those two groups. The precision with which difference in first and later evaluations was measured was important to the covariance of sires and sons. At lower Repeatabilities, age distribution for son's daughters could reflect a higher portion of second lactations and fewer terminal records. As sons' Repeatability increased, age distribution of his daughters and the percent of terminal records could have become more similar to that of his sire. For evaluations themselves, regressions increased slightly, then declined at high Repeatability of sons. Vinson (16) showed that regression of son on sire was independent of Repeatability of sire's evaluation for evaluation procedures not involving pedigree. Powe11 et al. (12) showed regression of son's evaluation on pedigree index to be independent of Repeatability of son, sire, or maternal grandsire. The increase from less than 30% Repeatability to 70 to 90% Repeatability has a parallel in the work of Rothschild et al. (13) who reported larger regressions when son's
TABLE 4. Regression (b), standard error (SE), and coefficient of determination (R ~) of son on sire for difference in milk evaluation (later minus first) for all breeds. I Difference, milk Breed
b
SE
R2
Ayrshire Guernsey Holstein AI Holsteins2 Jersey Brown Swiss
.15 .08 .10 .23 .11 .09NS
.06 .03 .01 .02 .03 .05
.02 .01 .01 .03 .01 .01
aAll regressions except those labeled NS were significant (P<.05). 2Sons entering artificial insemination (AI) prior to 40 mo of age.
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TABLE 5. Regression of son on sire for Holsteins with data stratified by son's all lactation Repeatability) Son's Repeatability for all lactations z >30 to -<<50
-<<30
5 5 0 to `<<70
>70 to `<<90
> 9 0 to `<<95
>95 to `<<99
>993
250
361
160
Number of pairs Records used in both son and sire evaluations
5,539
4,716
2,277
2,174
Regression coefficients First All Later Difference 4
.46 .54 .57 .02
.49 .56 .59 .11
First All Later Difference 4
.58 .65 .64 .03
.50 .50 .52 .01
.53 .61
.53 .60
.66
.63
.19
.25
.55 .57 .57 .31
.34 .42 .44 .26
.40 .46 .52 .33
.25 .26 .27 .05
.09 .13 .16 .05
.13 .17 .21 .09
Coefficients of determination .36 .37 .41 .02
.25 .28 .31 .04
1 Repeatabilities for all lactations for sires were required to exceed 90%. All regressions were significant (P<.05). 2 Standard errors of regression coefficients for son's repeatability groups were <30, .01;> 30 to `<<50, .01 to .02; >50 to `<<70, .02 to .03; > 7 0 to `<<90, .02 to .03; > 9 0 to `<<95, .06 to .08; >95 to `<<99, .05 to .06; >99, .08 to .09. 3Repeatabilities to three decimals were available. Only two digits are published for use in the industry. 4 Later evaluation minus first evaluation.
R e p e a t a b i l i t y was over 70% t h a n w h e n sons as low as 4 0 % were used. A t very high R e p e a t abilities, b o t h sons a n d sires are highly selected. Covariance w i t h i n t h e t o p t w o groups in T a b l e 5 m a y b e small d u e t o t h e p r e s e n c e o f o n l y t h e b e s t sons o f a few sires. Pedigree s e l e c t i o n for first a n d l a t e r evaluat i o n s is i m p o r t a n t for at least t w o reasons. First, AI s t u d s seeking t o m a x i m i z e progress in l i f e t i m e p r o f i t traits m a y wish to select sires of sons o n t h e basis o f s e p a r a t e e v a l u a t i o n s f o r first a n d l a t e r records. Second, t h e " a n c e s t e r merit" method of incorporating pedigree merit into MCC sire e v a l u a t i o n s is b a s e d o n p r e d i c t i o n e q u a t i o n s u s i n g all l a c t a t i o n d a t a f o r sires a n d MGS. Use o f first or l a t e r l a c t a t i o n p e d i g r e e d a t a f o r first o r later l a c t a t i o n e v a l u a t i o n s m a y b e m o r e desirable. M e a n s a n d s t a n d a r d d e v i a t i o n s f o r 8,055 Holstein sons w i t h e v a l u a t i o n s for first, all, a n d later r e c o r d s for t h e m s e l v e s , t h e i r sires, a n d M G S are in T a b l e 6. M e a n s for sons a n d sires
were h i g h e r f o r first, all, a n d later e v a l u a t i o n s in T a b l e 6 t h a n in T a b l e 1. S t a n d a r d d e v i a t i o n s for sons were slightly less t h a n T a b l e 2, especially for e v a l u a t i o n s of all l a c t a t i o n s . Sires o f t h e s e 8 , 0 5 5 sons were less variable t h a n sires o f all H o l s t e i n s in T a b l e 2 b u t were m o r e variable t h a n sires o f AI sons. R e p e a t a b i l i t i e s o f sons were very close t o t h o s e in T a b l e 1. T h e r e c o r d s w i t h sire a n d M G S d a t a a p p e a r m o r e similar to t h e e n t i r e H o l s t e i n file t h a n t o t h e AI Holsteins. Regression c o e f f i c i e n t s for sires a n d M G S are in T a b l e 7. E x p e c t e d regressions o f .5 a n d .25 were e x c e e d e d w h e n e v a l u a t i o n s u s e d to p r e d i c t s o n ' s e v a l u a t i o n were f r o m o t h e r t h a n first lactations. Intercepts for predicting son's e v a l u a t i o n d i f f e r e d b y u p t o 6 9 kg, d e p e n d i n g o n sire M G S e v a l u a t i o n s used. C o e f f i c i e n t s o f determination showed that most accurate p r e d i c t i o n s o c c u r r e d f r o m use o f all l a c t a t i o n e v a l u a t i o n s o n sires a n d MGS, regardless o f t h e l a c t a t i o n e v a l u a t i o n b e i n g p r e d i c t e d . Part o f t h e s e results c o u l d b e d u e to t h e way p e d i g r e e Journal of Dairy Science Vol. 68, No. 12, 1985
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TABLE 6. Means o f evaluations based on different lactations for 8,055 sons with evaluations available for sire and maternal grandsire (MGS). Means
Predicted Difference milk (PDM) First lactations All lactations Later lactations Difference~ Repeatability First lactations All lactations Later lactations Pedigree index milk 2 First lactations All lactations Later lactations
Standard deviation
Son
Sire
MGS
Son
Sire
MGS
--2 71 253 -232 40
-53 -94 -119 -66
--240 --277 -295 -55
258 265 267 145
331 310 304 139
339 310 296 149
.38 .44 .39
.94 .95 .95
.86 .89 .88
.21 .21 .19
--87 --116 --133
.16 .14 .15
.25 .22 .23
205 192 186
1 Later evaluation m i n u s first evaluation. 2.5 (sire's PDM) + .25 (MGS PDM).
m e r i t is i n c l u d e d in M C C . P e d i g r e e m e r i t o f a b u l l ' s sire a n d M G S is d e t e r m i n e d f r o m all lactation evaluations of those ancestors. T a b l e 8 u s e d PI i n s t e a d o f a c t u a l sire a n d MGS evaluations. Results are very similar to
T a b l e 7, as e x p e c t e d , b a s e d o n p a r t i a l reg r e s s i o n s o b t a i n e d f o r sire a n d M G S e v a l u a t i o n s . Intercepts differed by 60 kg or more depending o n r e c o r d s u s e d in t h e PI. T h e e x p e c t e d reg r e s s i o n o f 1.0 ( 1 2 ) w a s e x c e e d e d w h e n r e c o r d s
TABLE 7. Prediction of son's evaluation from evaluations on his sire and maternal grandsire (MGS) using 8,055 Holstein son-sire-MGS records. Lactation used
Lactation used in sire/MGS evaluations
in s o n ' s evaluation
First
First All Later
-187 --167 --147
All
Later
Intercepts (kg) -148 -126 -103
-127 -103 -- 78
Regression coefficients First Sire MGS All Sire MGS Later Sire MGS First All Later
.56 .54 .56
.46 .25
.50 .27
.50 .29
.47 .25
.51 .28
.52 .30
.48 .26
.53 .29
.54 .31
Coefficients of determination .59 .58 .61
All regressions are significant (P<.O1). Standard errors o f regression coefficients were less than .01. J o u r n a l o f Dairy Science Vol. 68, No. 12, 1985
.57 .57 .61
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TABLE 8. Prediction of son's evaluation from pedigree index) Records used in son's evaluation
First
Records used in pedigree index All
Later
First All Later
-189 -170 --149
Intercepts (kg) -152 --130 --107
-132 --109 --84
Regression coefficients First All Later
.94 .95 .98
First All Later
.56 .54 .56
1.03 1.05 1.09 Coefficients of determination .59 .58 .61
1.04 1.07 1.12 .57 .57 .61
1.5 Sire's evaluation + .25 maternal grandsire evaluation. All regressions significant (P<,O1). Standard errors of regression coefficients were .01 or less.
after the first were used in Pl. The R 2 favored use of all lactation evaluations for prediction of son's evaluations. Because the R 2 in Tables 7 and 8 were identical, there appeared to be no advantages to using sire and MGS evaluation separately instead of PI. Results of this study show that differences i n first and later lactation evaluations are transmittable from sire to son, establishing a genetic basis for differences seen in earlier work (3, 5). The accuracy with which son's difference can be predicted is a function of Repeatability . Further, use of all lactations after the first in later evaluations may make differences more difficult to predict from MCC data than was the case for Bar-Anan (1) using Israeli evaluations. In MCC data, sons needed fairly high Repeatabilities before differences between evaluations could be predicted. High Repeatabilities for sons' evaluations could serve to equalize age distribution o f daughters of sires and sons for later records in this analysis. If sires of sons were selected for difference (favoring either later or first evaluations), progress in the direction desired could be achieved at a rate somewhat slower than for the individual evaluations. Sire-son relationships for evaluations from first, all, and later records showed all lactation evaluations to have the most utility in predicting
evaluations from any of the three groups of records. First records were less useful predictors (in terms of R 2) than were later record evaluations in most cases. To a certain extent, these results are due to the present method of utilizing ancestor merit in the MCC. Prediction equations derived from all records are currently used regardless of the lactations involved in an evaluation. Use of first (or later) lactation evaluation pedigree data for first (or later) lactation sire evaluations may be superior to the present procedure, but such a conclusion is beyond the scope of this study. Regression of son evaluation on sire or MGS evaluation increased when later records were included. The same effect was seen for PI. One explanation of such a result would be the impact of terminal records on sire evaluations. Sires and MGS, being older, would have opportunity for a higher portion of daughters to have terminal records than would their sons and grandsons. If terminal records suppress differences among sires, the results observed in this study would be expected. ACKNOWLEDGMENTS
The authors are indebted to the staff of the Animal Improvement Programs Laboratory, Behsville, MD, for their cooperation and partial financial support of this project. Journal of Dairy Science Vol. 68, No. 12, 1985
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CASSELL ET AL. REFERENCES
1 Bar:Anan, R., M. Ron, and G. R. Wiggans. 1983. Associations a m o n g progeny tests of single or pooled lactations. J. Dairy Sci. 66:595. 2 Butcher, K. R., and J. E. Legates. 1976. Estimating son's progeny test from his pedigree information. J. Dairy Sci. 59:137. 3 Cassell, B. G., J. S. Clay, and H. D. Norman. 1985. Differences in modified c o n t e m p o r a r y comparison sire evaluations from first and later lactations by breed. J. Dairy Sci. 68:1778. 4 Cassell, B. G., and B. T. McDaniel. 1983. Use of later records in dairy sire evaluation: a review. J. Dairy Sci. 66:1. 5 Cassell, B. G., B. T. McDaniel, and H. D. Norman. 1983. Modified C o n t e m p o r a r y Comparison sire evaluations from first, all, and later lactations. J. Dairy Sci. 66:140. 6 Cassell, B. G., B. T. McDaniel, and H. D. Norman. 1983. Modified C o n t e m p o r a r y Comparisons for first and second lactations in t h e same and different herds. J. Dairy Sci. 66:315. 7 Cassell, B. G., B. T. McDaniel, and H. D. Norman. 1983. Impact of culling on Modified C o n t e m p o r a r y Comparison sire evaluations. J. Dairy Sci. 66 : 1359. 8 Cassell, B. G., B. T. McDaniel, and O. W. Robison. 1983. Impact of culling on sire evaluations by m i x e d model procedures. J. Dairy Sci. 66:1696. 9 Henderson, C. R. 1975. Best linear unbiased estimation and prediction under a selection model. Biometrics 31:423. 10 Lofgren, D. L., B. G. Cassell, H. D. Norman, and B. T. McDaniel. 1983. Effects of culling on sire evaluations by mixed models. J. Dairy Sci. 66:2418. 11 Nicholson, H. H., L. R. Schaeffer, E. B. Burnside, and M. G. Freeman. 1978. Use of later records in
Journal o f Dairy Science Vol. 68, No. 12, 1985
dairy sire evaluation. Can. J. Anita. Sci. 58:615. 12 Powell, R. L., H. D. Norman, and F. N. Dickinson. 1977. Relationships between bulls' pedigree indexes and daughter performance in the Modified C o n t e m p o r a r y Comparison. J. Dairy Sci. 60:961. 13 Rothschild, M. F., L. W. Douglass, and R. L. Powell. 1981. Prediction o f son's Modified Cont e m p o r a r y Comparison from pedigree information. J. Dairy Sci. 64:331. 14 Schaeffer, L. R. 1981. Pedigree i n d e x i n g o f Holstein bulls used in artificial insemination. Can. J. A n i m . Sci. 61:261. 15 Ufford, G. R., C. R. Henderson, J. F. Keown, and L. D. Van Vleck. 1979. Accurracy o f first lactation versus all lactation sire evaluations by best linear unbiased predictions. J. Dairy Sci. 62:603. 16 Vinson, W. E. 1983. Effects of selection and errors of prediction on relationships between progeny tests o f sires and sons. J. Dairy Sci. 66:359. 17 Vinson, W. E., and J. M. White. 1982. Prediction of Modified C o n t e m p o r a r y Comparisons from pedigree information for artificial insemination and natural service hulls. J. Dairy Sci. 65:1578. 18 Weller, J. I., H. D. N o r m a n , and G. R. Wiggans. 1984. Weighting sire evaluations on different parities to estimate overall merit. J. Dairy Sci. 67:1030. 19 Weller, J. I., H. D. N o r m a n , and G. R. Wiggans. 1984. Sire evaluations with parities as correlated traits and comparison with single-trait evaluations. J. Dairy Sci. 67:2010. 20 Wickham, B. W., and C. R. Henderson. 1977. Sire evaluation by second lactation records of daughters. J. Dairy Sci. 60:96. 21 Wiggans, G. R., and R. L. Powell. 1984. Increasing pedigree contribution to dairy sire evaluation. J. Dairy Sci. 67:893.
INTRODUCTION
January 1984 Modified Contemporary Comparison sire evaluations for first, all, and later records were used to create sire-son pairs in five dairy breeds. Each evaluation for each bull included 10 or more daughters. Regressions of son on sire for evaluations for first, all, or later records exceeded the expectation of .5 and were most divergent for Jerseys and Brown Swiss. Regressions and coefficients of determination were generally highest when sire's evaluation based on all records predicted sons' evaluations from first, all, or later records. Regression of son on sire for difference in evaluations (later minus first) was positive in all breeds, ranging from .08 to .10, and was significant for all breeds except Brown Swiss. Coefficients of determination were low (.01 to .02). Both regression of son on sire for difference and coefficient of determination increased with son's Repeatability, with a regression of .33 and a coefficient of determination of .09 for sons over 99% Repeatability, Regressions for 8,055 Holsteins with evaluations for sires and maternal grandsires on those ancestors were .46 to .54 for sires and .25 t o . 31 for maternal grandsires. Regressions of son's evaluation on pedigree index were .94 for first, 1.05 for all, and 1.12 for later lactations.
The choice of lactations to include in sire evaluations recently has been reviewed (4). Later lactations are important to the economic health of the dairy herd as they occur with greater frequency and at higher yields than first records. Computationally, such records are difficult to include in sire evaluation and are subject to culling bias (7, 8, 9, 10, 11, 12) unless proper models are used. However, later records increase the accuracy of evaluations (5, 6, 15, 20) through additional information and more ties among sires. Further, they have been shown (3, 5, 19) to affect sire rank with important variation from sire to sire in difference between evaluations based on first and later records. The importance o f later records to accurate sire rankings suggests that relationships among sires, MGS, and sons should be examined for evaluations based on first, all, and later records. Such relationships have been examined for all lactation evaluations by Powell et al. (12) for all breeds. These workers found a regression of near 1.0 for average Modified Contemporary Deviation on pedigree index (PI). Rothschild et al. (13) reported correlations between son and sire near expectation for Modified Contemporary Comparison (MCC) sire evaluations. Vinson and White (17) regressed son MCC evaluations from all lactations on sire and MGS evaluations (by approximate MCC methods) from first records. Results varied b y type of sampling [artificial insemination (AI) or not] but were consistently less than expectation (.26 to .41 for sires and .11 to .17 for MGS). Whether use of different records in evaluations of sires, and sons accounted for differences from expected values is not known. Differences in sire evalua-
Received April 25, I985. 1985 J Dairy Sci 68:3291-3300
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CASSELL ET AL.
tion methodology could be involved. Schaeffer's (14) work with first lactation Canadian evaluations yielded partial regression coefficients of .497 for sires and .243 for MGS; results were very near the expected .5 and .25. The difference in evaluations from first and later records has implications for net present value of semen from different bulls (18). Such differences could be important, if they proved transmittable, in selecting sires of sons. Bar-Anan et al. (1), using Israeli sire evaluations from first, second, third, and pooled lactations, reported a regression coefficient of .49 for son on sire for change from first to second evaluation. Variation of sons within sire was large. No such estimates exist for MCC evaluations. The purpose of this study was to examine the regression of son on sire for evaluations based on different parities for five major dairy breeds. The utility of pedigree evaluations from first, all, and later records was of interest. The study also was to determine if the differences in rate of maturity apparent in previous studies had a genetic basis or were simply a function of unaccounted environmental sources of variation or biases due to female culling. MATERIALS AND METHODS
Data were all sire evaluations for milk in Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss breeds from the January 1984 MCC. Published evaluations utilize all lactations. However, separate evaluations from first records and later records are routinely calculated in the MCC and were used in the study. Each evaluation included at least 10 daughters. Each bull's record contained sire and MGS identification. Two hundred sixty-two Ayrshire, 1,130 Guernsey, 17,882 Holstein, 3,920 Jersey, and 475 Brown Swiss sire-son pairs in which sires and sons had genetic evaluations were created. Sire records were repeated for each son in the data. Holstein records were further divided to include a group of 3,920 sire-son pairs in which the son entered AI service prior to 40 mo of age. Regressions of son on sire were calculated for all nine combinations of first, all, and later lactation evaluations for sires and sons in each breed. In Holsteins, a further match on MGS produced 8,055 records with evaluations from first, all, and later records on sons, sires, and
Journal of Dairy Science Vol. 68, No. 12, 1985
MGS. From these records, PI was calculated as PI -- .5 (sire PDM), + .25 (MGS PDM) where PDM is Predicted Difference Milk. January 1984 MCC used the PD 82 genetic base and the "ancestor merit" method (21) of incorporating pedigree information into sire evaluations. RESULTS A N D DISCUSSION
Means of evaluations and their Repeatabilities for sires and sons in each breed are in Table 1. Average evaluations for sires exceeded those for sons in most cases. Average differences (later minus first evaluation) were positive for sons but negative for sires in all breeds except Brown Swiss. Cassell et al. (3) reported differences of 36, 0, 6, 35, and 35 kg for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss sires using these same data. Negative differences for sires could be due to inclusion of higher percentages of terminal records in their later evaluations. Cassell et al. (6) reported a larger positive difference for 200 widely used Holstein sires when later records were restricted to second lactations only compared to all later records. That study and the current study suggest that terminal records depress later lactation evaluations relative to first lactation evaluations. Differences in genetic trend from first and later records could also be involved. Cassell et al. (3, 5) reported negative correlations ( - . 1 8 to - . 2 5 ) between sire's age and difference in evaluations. Average Repeatabilities indicated that most sons were not used in AI whereas most sires were. Average Repeatabilities were always highest for all lactation evaluations, as expected, since first and later evaluations are subsets. Repeatabilities for later evaluation were almost always higher than for first evaluations, although such differences would be expected to be minor, because for most sires, additional data in later evaluations would be from additional records on the same daughters. Standard deviations of evaluations and Repeatabilities are in Table 2. In all breeds except AI Holsteins, sire evaluations were more variable than son evaluations. This result is expected from selection index theory and results from the low average Repeatability of son evaluations and their subsequent regression toward pedigree predictions. For A1 Holsteins, sons' evaluations were not regressed as heavily
TABLE 1. Means of evaluations based on different lactations for sires and sons. Holstein
O
Number of pairs Predicted Difference milk, kg First lactations Son Sire All lactations Son Sire Later lactations Son Sire Difference 2 Son Sire Repeatabilities First lactations Son Sire All lactations Son Sire Later lactations Son Sire
Ayrshire
Guernsey
All
AI 1
Jersey
Brown Swiss
262
1,130
17,882
3,920
1,509
475
-239 -155
-295 -234
-342 --151
-174 57
-294 -199
--342 --337
-222 -176
-290 -269
--331 --190
-148 6
-272 -213
--332 --341
-232 -180
-280 -280
--316 -212
-118 -27
-245 -201
--329 --318
5 -25
15 -46
26 --61
56 -84
50 -2
14 19
O
Fo O0
Z
.34 .74
.32 .79
.37 .92
.67 .98
.35 .82
.34 .73
.42 .80
.37 .83
.44 .94
.74 .99
.41 .86
.42 .79
.38 .78
.33 .81
.39 .93
.66 .99
.37 .84
.38 .77
O
Z
0 Z
>
< Ox O0
t~
1 Sons entering artificial insemination (AI) prior to 40 mo of age. z Later lactation evaluation minus first lactation evaluation.
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CASSELL ET AL.
TABLE 2. Standard deviations of evaluations based on different lactations for sires and sons. Holstein
Predicted Difference milk, kg First lactations Son Sire All lactations Son Sire Later lactations Son Sire Difference 2 Son Sire Repeatabilities First lactations Son
Sire All lactations Son Sire Later lactations Son Sire
Ayrshire
Guernsey
All
AIl
Jersey
Brown Swiss
215 280
173 201
262 357
263 255
239 289
273 305
216 258
187 202
273 335
269 243
247 278
267 292
199 241
185 203
276 325
268 246
241 268
229 269
118 113
99 102
143 143
176 134
93 82
139 125
•18 •28
.16 .27
.21 .19
.16 .06
.19 .25
.18 .27
.19 .24
.17 .24
.22 .17
.14 .05
.20 .22
.19 .24
.18
.16
.20
.17
.18
.17
•2 5
.25
.18
.05
.23
.25
Sons entering artificial insemination (AI) prior to 40 mo of age. 2 Later lactation evaluation minus first lactation evaluation. and sires were m o r e carefully selected as evidenced by the higher means in Table 1. In m o s t breeds, sire evaluations f r o m first records were m o r e variable than evaluations f r o m all or later records. First evaluations were m o r e variable for sons in Brown Swiss. Average differences b e t w e e n evaluations f r o m first, all, and later records are d e t e r m i n e d by the genetic bases established for each breed and evaluation. Standard deviations of difference reflect variation f r o m sire to sire in such differences. This variation could be of e c o n o m i c importance. Cassell et al. (3) r e p o r t e d standard deviations o f difference of 114, 94, 142, 91, and 134 kg for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss f r o m these data. Only Holstein AI sons deviated greatly f r o m these standard deviations. S o m e o f these sons could still be adding daughter i n f o r m a t i o n to their evaluations, a situation that could give rise to sample differences b e t w e e n first and later evaluations. Standard deviations o f Repeatabilities were greater for sires than sons e x c e p t for AI HolJournal of Dairy Science Vol. 68, No. 12, 1985
steins, where high Repeatability sires pred o m i n a t e d . Low standard deviations of son Repeatabilities and low averages in Table 1 indicate that m o s t sons in the data were used only in natural service. Regressions o f son evaluations on sire evaluations are in Table 3. For pairs of evaluations based on the same record groups, the e x p e c t a t i o n of these regressions is .5 (16). Vinson (16) cautioned that empirical regressions could be influenced substantially by part-whole relationships (sire's evaluation in ancester m e r i t p o r t i o n o f MCC) when son's Repeatability was "small". Further, the e x p e c t a t i o n is based on the assumption that genetic merit of MGS is u n c o r r e l a t e d with genetic merit of sires of sons. The validity of such an assumption may be questionable across the years represented in these data. Where record groups differ, such as regression of son's first evaluation on sire's later evaluation, the e x p e c t a t i o n includes terms involving genetic correlation among first and second, third, or subsequent records and w o u l d be less than .5. Because we had no knowledge
SIRE-SON RELATIONSHIPS
3295
TABLE 3. Regression (b) and coefficient of determination (R 2) of son on sire for milk evaluations based on different lactations.1,2 Lactations used in sire's evaluation Lactations used in sons's evaluations Ayrshire First All Later
Guernsey First All Later Holstein, All First All Later
Holstein, AI 3 First All Later Jersey First All Later Brown Swiss First
All Later
First
All
Later
b
R2
b
R=
b
R2
.56 .54 .49
.52 .49 .47
.63 .62 .56
.56 .54 .53
.65 .65 .60
.54 .53 .52
.60 .64 .64
.48 .47 .49
.62 .67 .68
.53 .53 .55
.60 .66 .67
.50 .51 .54
.52 .54 .55
.50 .49 .51
.57 .59 .61
.53 .53 .55
.58 .61 .63
.51 .52 .55
.50 .50 .51
.23 .22 .23
.53 .56 .59
.24 .25 .29
.50 .54 .58
.22 .24 .29
.65 .66 .65
.61 .59 .61
.68 .70 .70
.63 .62 .64
.70 .72 .72
.62 .61 .64
.63 .62 .54
.50 .51 .51
.67 .66 .57
.52 .52 .53
.71 .70 .61
.50 .49 .51
All regressions significant (P<.05). 2Standard errors of regressions were: Ayrshire, .03 to .04; Guernsey, .02; Holstein (all), .004; Holstein (AI), .01 to .02; Jersey, .01 ; and Brown Swiss, .02 to .03. 3 Sons entering artificial insemination (AI) prior to 40 mo of age.
o f t h e p r o p o r t i o n o f s e c o n d , third, a n d subseq u e n t r e c o r d s in each b u l l ' s e v a l u a t i o n s , n o a t t e m p t was m a d e t o derive a precise e x p e c t a t i o n . Finally, r e l a t i o n s h i p s b e t w e e n first or later a n d all l a c t a t i o n e v a l u a t i o n s are p a r t - w h o l e in n a t u r e , as s o m e c o m m o n r e c o r d s w o u l d a p p e a r in b o t h e v a l u a t i o n s . All regressions e x c e p t s o n ' s later o n sire's first e v a l u a t i o n s in A y r s h i r e s were a b o v e .5. Powell et al. (12) f o u n d regressions c e n t e r e d o n e x p e c t a t i o n s while t h o s e o f V i n s o n a n d White ( 1 7 ) were c o n s i s t e n t l y less t h a n e x p e c t e d . T h e g r e a t e s t d i f f e r e n c e s a b o v e e x p e c t e d values in t h e p r e s e n t s t u d y were for Jerseys, as previously o b s e r v e d (2, 12). O n e r e a s o n f o r regression o f s o n o n sire to e x c e e d e x p e c t a t i o n w o u l d b e positive c o v a r i a n c e s b e t w e e n evaluat i o n s o f sires a n d MGS. If such a c o v a r i a n c e
existed, regression o f s o n ' s PD o n sire a n d M G S s i m u l t a n e o u s l y s h o u l d p r o d u c e regression closer t o e x p e c t e d .5 a n d .25. T a b l e 7 s h o w s t h e results o f such a m o d e l for 8 , 0 5 5 H o l s t e i n bulls w i t h e v a l u a t i o n s o n sire a n d m a t e r n a l grandsire. Results are closer t o e x p e c t e d values t h a n t h o s e in T a b l e 3 f o r all a n d l a t e r l a c t a t i o n e v a l u a t i o n s . Regressions using first l a c t a t i o n e v a l u a t i o n s o f sires were c o n s i s t e n t l y l o w e r t h a n t h o s e using e v a l u a t i o n s f r o m all or l a t e r r e c o r d s o f sires. Such c o m p a r i s o n s c a n b e i n f l u e n c e d b y t h e v a r i a t i o n in t h e e v a l u a t i o n s o f sires if c o v a r i a n c e b e t w e e n sires a n d sons are stable. S t a n d a r d i z e d regression c o e f f i c i e n t s w e r e m u c h m o r e similar across r e c o r d sets u s e d in sire e v a l u a t i o n s t h a n t h o s e in T a b l e 3 b u t w e r e c o n s i s t e n t l y l o w e r f o r first l a c t a t i o n e v a l u a t i o n s o f sires. C o e f f i c i e n t s o f d e t e r m i n a t i o n (R 2) Journal of Dairy Science Vol. 68, No. 12, 1985
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CASSELL ET AL.
indicate the accuracy with which son's performance can be predicted by sire's evaluations. The R z from using sire evaluations from all lactations exceeded those from first in all cases and those from later in 15 of 18 cases. This was the expected result because of the additional data in all lactation evaluations and the partwhole nature of the relationships. Evaluations for sons are partly determined by sire and maternal grandsire genetic merit (21). All lactation evaluations for sires and maternal grandsires are used for this purpose, regardless of the records involved in sons' evaluations. The R 2 for the AI Holstein subset were considerably lower than other results in Table 3. Holstein AI sons had higher Repeatabilities than other Holstein sons and their evaluations were less affected by the PD of their sire through the ancestor merit portion of the PD equation. As more daughter information becomes available on sons, their evaluations will deviate from pedigree predictions. The net effect is a lowering of R z with little effect on the regression coefficients. Table 2 also shows lower standard deviations of evaluations for sires of AI sons, which is evidence that these sires were more carefully selected than sires of all sons. Such selection will bias downward correlation between sires and sons, thus reducing R 2' A major objective of the study was to determine the relationship between differences in first and later lactation evaluations for sires and sons. Differences in first and later lactation evaluations reflect differences in rate of maturity of daughters. Results are in Table 4. Regressions were positive in all breeds and significantly greater than zero except for Brown Swiss. Tendencies for a sire's daughters to produce more (or less) in later lactations than they did in first lactations were transmittable to daughters of a son. Our ability to predict differences for individual bulls was poor as shown by low R 2. Difference between first and later lactation evaluations can be affected by the sample of daughters in each evaluation, by the age of daughters involved, by the presence of terminal records, and by differences in rate of maturity. Thus, low R 2 are not surprising for the average Repeatabilities (.34 to .44) of sons involved in this study. Both regressions and R 2 increased for AI Holsteins for difference in later and first Journal of Dairy Science Vol. 68, No. 12, 1985
evaluations. To examine the extent of this trend, Table 5 was created by limiting the Holstein data to sires over 90% Repeatability for all lactations and subsetting sons on the basis of all lactation Repeatability. The regression of son on sire for difference increased from .02 for sons with Repeatabilities less than 30% to .33 for sons with Repeatabilities above 99%. The R 2 increased from .03 to .09 for those two groups. The precision with which difference in first and later evaluations was measured was important to the covariance of sires and sons. At lower Repeatabilities, age distribution for son's daughters could reflect a higher portion of second lactations and fewer terminal records. As sons' Repeatability increased, age distribution of his daughters and the percent of terminal records could have become more similar to that of his sire. For evaluations themselves, regressions increased slightly, then declined at high Repeatability of sons. Vinson (16) showed that regression of son on sire was independent of Repeatability of sire's evaluation for evaluation procedures not involving pedigree. Powe11 et al. (12) showed regression of son's evaluation on pedigree index to be independent of Repeatability of son, sire, or maternal grandsire. The increase from less than 30% Repeatability to 70 to 90% Repeatability has a parallel in the work of Rothschild et al. (13) who reported larger regressions when son's
TABLE 4. Regression (b), standard error (SE), and coefficient of determination (R ~) of son on sire for difference in milk evaluation (later minus first) for all breeds. I Difference, milk Breed
b
SE
R2
Ayrshire Guernsey Holstein AI Holsteins2 Jersey Brown Swiss
.15 .08 .10 .23 .11 .09NS
.06 .03 .01 .02 .03 .05
.02 .01 .01 .03 .01 .01
aAll regressions except those labeled NS were significant (P<.05). 2Sons entering artificial insemination (AI) prior to 40 mo of age.
SIRE-SON RELATIONSHIPS
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TABLE 5. Regression of son on sire for Holsteins with data stratified by son's all lactation Repeatability) Son's Repeatability for all lactations z >30 to -<<50
-<<30
5 5 0 to `<<70
>70 to `<<90
> 9 0 to `<<95
>95 to `<<99
>993
250
361
160
Number of pairs Records used in both son and sire evaluations
5,539
4,716
2,277
2,174
Regression coefficients First All Later Difference 4
.46 .54 .57 .02
.49 .56 .59 .11
First All Later Difference 4
.58 .65 .64 .03
.50 .50 .52 .01
.53 .61
.53 .60
.66
.63
.19
.25
.55 .57 .57 .31
.34 .42 .44 .26
.40 .46 .52 .33
.25 .26 .27 .05
.09 .13 .16 .05
.13 .17 .21 .09
Coefficients of determination .36 .37 .41 .02
.25 .28 .31 .04
1 Repeatabilities for all lactations for sires were required to exceed 90%. All regressions were significant (P<.05). 2 Standard errors of regression coefficients for son's repeatability groups were <30, .01;> 30 to `<<50, .01 to .02; >50 to `<<70, .02 to .03; > 7 0 to `<<90, .02 to .03; > 9 0 to `<<95, .06 to .08; >95 to `<<99, .05 to .06; >99, .08 to .09. 3Repeatabilities to three decimals were available. Only two digits are published for use in the industry. 4 Later evaluation minus first evaluation.
R e p e a t a b i l i t y was over 70% t h a n w h e n sons as low as 4 0 % were used. A t very high R e p e a t abilities, b o t h sons a n d sires are highly selected. Covariance w i t h i n t h e t o p t w o groups in T a b l e 5 m a y b e small d u e t o t h e p r e s e n c e o f o n l y t h e b e s t sons o f a few sires. Pedigree s e l e c t i o n for first a n d l a t e r evaluat i o n s is i m p o r t a n t for at least t w o reasons. First, AI s t u d s seeking t o m a x i m i z e progress in l i f e t i m e p r o f i t traits m a y wish to select sires of sons o n t h e basis o f s e p a r a t e e v a l u a t i o n s f o r first a n d l a t e r records. Second, t h e " a n c e s t e r merit" method of incorporating pedigree merit into MCC sire e v a l u a t i o n s is b a s e d o n p r e d i c t i o n e q u a t i o n s u s i n g all l a c t a t i o n d a t a f o r sires a n d MGS. Use o f first or l a t e r l a c t a t i o n p e d i g r e e d a t a f o r first o r later l a c t a t i o n e v a l u a t i o n s m a y b e m o r e desirable. M e a n s a n d s t a n d a r d d e v i a t i o n s f o r 8,055 Holstein sons w i t h e v a l u a t i o n s for first, all, a n d later r e c o r d s for t h e m s e l v e s , t h e i r sires, a n d M G S are in T a b l e 6. M e a n s for sons a n d sires
were h i g h e r f o r first, all, a n d later e v a l u a t i o n s in T a b l e 6 t h a n in T a b l e 1. S t a n d a r d d e v i a t i o n s for sons were slightly less t h a n T a b l e 2, especially for e v a l u a t i o n s of all l a c t a t i o n s . Sires o f t h e s e 8 , 0 5 5 sons were less variable t h a n sires o f all H o l s t e i n s in T a b l e 2 b u t were m o r e variable t h a n sires o f AI sons. R e p e a t a b i l i t i e s o f sons were very close t o t h o s e in T a b l e 1. T h e r e c o r d s w i t h sire a n d M G S d a t a a p p e a r m o r e similar to t h e e n t i r e H o l s t e i n file t h a n t o t h e AI Holsteins. Regression c o e f f i c i e n t s for sires a n d M G S are in T a b l e 7. E x p e c t e d regressions o f .5 a n d .25 were e x c e e d e d w h e n e v a l u a t i o n s u s e d to p r e d i c t s o n ' s e v a l u a t i o n were f r o m o t h e r t h a n first lactations. Intercepts for predicting son's e v a l u a t i o n d i f f e r e d b y u p t o 6 9 kg, d e p e n d i n g o n sire M G S e v a l u a t i o n s used. C o e f f i c i e n t s o f determination showed that most accurate p r e d i c t i o n s o c c u r r e d f r o m use o f all l a c t a t i o n e v a l u a t i o n s o n sires a n d MGS, regardless o f t h e l a c t a t i o n e v a l u a t i o n b e i n g p r e d i c t e d . Part o f t h e s e results c o u l d b e d u e to t h e way p e d i g r e e Journal of Dairy Science Vol. 68, No. 12, 1985
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TABLE 6. Means o f evaluations based on different lactations for 8,055 sons with evaluations available for sire and maternal grandsire (MGS). Means
Predicted Difference milk (PDM) First lactations All lactations Later lactations Difference~ Repeatability First lactations All lactations Later lactations Pedigree index milk 2 First lactations All lactations Later lactations
Standard deviation
Son
Sire
MGS
Son
Sire
MGS
--2 71 253 -232 40
-53 -94 -119 -66
--240 --277 -295 -55
258 265 267 145
331 310 304 139
339 310 296 149
.38 .44 .39
.94 .95 .95
.86 .89 .88
.21 .21 .19
--87 --116 --133
.16 .14 .15
.25 .22 .23
205 192 186
1 Later evaluation m i n u s first evaluation. 2.5 (sire's PDM) + .25 (MGS PDM).
m e r i t is i n c l u d e d in M C C . P e d i g r e e m e r i t o f a b u l l ' s sire a n d M G S is d e t e r m i n e d f r o m all lactation evaluations of those ancestors. T a b l e 8 u s e d PI i n s t e a d o f a c t u a l sire a n d MGS evaluations. Results are very similar to
T a b l e 7, as e x p e c t e d , b a s e d o n p a r t i a l reg r e s s i o n s o b t a i n e d f o r sire a n d M G S e v a l u a t i o n s . Intercepts differed by 60 kg or more depending o n r e c o r d s u s e d in t h e PI. T h e e x p e c t e d reg r e s s i o n o f 1.0 ( 1 2 ) w a s e x c e e d e d w h e n r e c o r d s
TABLE 7. Prediction of son's evaluation from evaluations on his sire and maternal grandsire (MGS) using 8,055 Holstein son-sire-MGS records. Lactation used
Lactation used in sire/MGS evaluations
in s o n ' s evaluation
First
First All Later
-187 --167 --147
All
Later
Intercepts (kg) -148 -126 -103
-127 -103 -- 78
Regression coefficients First Sire MGS All Sire MGS Later Sire MGS First All Later
.56 .54 .56
.46 .25
.50 .27
.50 .29
.47 .25
.51 .28
.52 .30
.48 .26
.53 .29
.54 .31
Coefficients of determination .59 .58 .61
All regressions are significant (P<.O1). Standard errors o f regression coefficients were less than .01. J o u r n a l o f Dairy Science Vol. 68, No. 12, 1985
.57 .57 .61
SIRE-SON RELATIONSHIPS
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TABLE 8. Prediction of son's evaluation from pedigree index) Records used in son's evaluation
First
Records used in pedigree index All
Later
First All Later
-189 -170 --149
Intercepts (kg) -152 --130 --107
-132 --109 --84
Regression coefficients First All Later
.94 .95 .98
First All Later
.56 .54 .56
1.03 1.05 1.09 Coefficients of determination .59 .58 .61
1.04 1.07 1.12 .57 .57 .61
1.5 Sire's evaluation + .25 maternal grandsire evaluation. All regressions significant (P<,O1). Standard errors of regression coefficients were .01 or less.
after the first were used in Pl. The R 2 favored use of all lactation evaluations for prediction of son's evaluations. Because the R 2 in Tables 7 and 8 were identical, there appeared to be no advantages to using sire and MGS evaluation separately instead of PI. Results of this study show that differences i n first and later lactation evaluations are transmittable from sire to son, establishing a genetic basis for differences seen in earlier work (3, 5). The accuracy with which son's difference can be predicted is a function of Repeatability . Further, use of all lactations after the first in later evaluations may make differences more difficult to predict from MCC data than was the case for Bar-Anan (1) using Israeli evaluations. In MCC data, sons needed fairly high Repeatabilities before differences between evaluations could be predicted. High Repeatabilities for sons' evaluations could serve to equalize age distribution o f daughters of sires and sons for later records in this analysis. If sires of sons were selected for difference (favoring either later or first evaluations), progress in the direction desired could be achieved at a rate somewhat slower than for the individual evaluations. Sire-son relationships for evaluations from first, all, and later records showed all lactation evaluations to have the most utility in predicting
evaluations from any of the three groups of records. First records were less useful predictors (in terms of R 2) than were later record evaluations in most cases. To a certain extent, these results are due to the present method of utilizing ancestor merit in the MCC. Prediction equations derived from all records are currently used regardless of the lactations involved in an evaluation. Use of first (or later) lactation evaluation pedigree data for first (or later) lactation sire evaluations may be superior to the present procedure, but such a conclusion is beyond the scope of this study. Regression of son evaluation on sire or MGS evaluation increased when later records were included. The same effect was seen for PI. One explanation of such a result would be the impact of terminal records on sire evaluations. Sires and MGS, being older, would have opportunity for a higher portion of daughters to have terminal records than would their sons and grandsons. If terminal records suppress differences among sires, the results observed in this study would be expected. ACKNOWLEDGMENTS
The authors are indebted to the staff of the Animal Improvement Programs Laboratory, Behsville, MD, for their cooperation and partial financial support of this project. Journal of Dairy Science Vol. 68, No. 12, 1985
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