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Genetic Differences Among Holstein-Friesian Herd Improvement Registry Herds1
Genetic Differences Among Holstein-Friesian Herd Improvement Registry Herds 1 F. J. MORILLO 2 and J. E. LEGATES
Department of Animal Science North Carolina State University, Raleigh 27607 Abstract
Genetic differences among 442 HolsteinFriesian I:fIR herds that had been on test from March, 1952, to April, 1961, were examined. F i r s t lactations initiated at under 36 months of age for 37,890 individuals were studied by two approaches. I n the first, differences between bull breeder herds were compared by the progeny test evaluation of sires produced in a specific herd but progeny tested in another herd. Among 19 breeder herds that sold a large number of sons to other herds, four times the variance of breeding values of those sons, attributable to the herd in which they were bred, represented 12.4 and 18.7% of the herd component for milk yield and per cent fat. The mean genetic merit of 282 sons originating from these breeder herds was 92 kg o£ milk above the 479 sons from nonbreeder herds and 143 kg above the 67 sires originating from outside the United States. The second approach involved a comparison of the herd component of variance from multiherd progenies of sires with the herd component from single-herd progenies. The fraction of the herd variance for the population of 442 herds that was genetic was 9.3% for milk yield and 8.9% for f a t per cent. The results indicate that the genetic differences among these Holstein H I R herds are small but real, contributing about 10% of the variance among herd averages for milk. While the herd average would be more useful to correct for environmental differences among herds, it also should receive some positive attention for estimating genetic differences between individuals in different herds.
Received for publication November 14, 1969. 1 Paper no. 3023 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh. Computing services for this investigation were supported by Public Health Service Grant FR-00011. z Present address: Director of Research of the Ministry of Agriculture, Caracas, Venezuela.
Knowledge of the fraction of herd differences which are genetic is important in the formulation of sire evaluation procedures. Likewise, in choosing among females in different herds, as in the choice of dams of young sires, such genetic differences may warrant consideration. I n most attempts to examine the magnitude of the genetic differences between herds, existing production data have been utilized (4,6,9-11). Other studies of between-herd exchanges of monozygotic females have provided an experimental approach (2,10). Most of the results are in general agreement that genetic differences among herds within breeds for milk and f a t yields are small but real. This study was undertaken to determine the genetic differences among Holstein-Friesian bull breeding ("breeder") herds and also to examine the magnitude of the genetic differences among a population of 442 Holstein-Friesian HtIR herds. Data and Methods
Two approaches were used to examine the magnitude of genetic differences among groups of herds from a population of 442 Holstein I-IIl~ herds on test from March, 1952, to April, 1961. F i r s t lactations initiated at under 36 months of age for 37,890 individuals were studied. The first approach was that of Robertson and McArthur (10), in which herds were compared on the basis of estimated breeding values, unadjusted breeding values of Morillo and Legates (7), of sires produced in a specified herd but progeny tested in another herd. The second approach involved a comparison of the herd component of variance for multiherd progenies of sires with the herd component [from single-herd progenies as suggested by McGilliard (6)]. I n the first phase of the study, estimated breeding values for 828 sires bred aud proved in different herds were utilized. These breeding values were based on regressed deviations from the adjusted herdmate average for a minimum of 8 progeny in a herd (7). "Breeder" herds were herds having a minimum of 5 sons with a progeny test in a nonbreeder herd. A t least one of the parents of the sons had to be bred 908
909
G E N E T I C DIF:FERENCES
in the breeder herd. There were 19 breeder herds with 282 sons, of which 261 met the essential requirements. Breeding values for each sire (gik) expressed as deviations from the population mean were described and analyzed according to the following model : gik : bi -[- elk where bi is the effect of the i th breeder herd and eik is an effect peculiar to the k tu sire bred in the i th herd.
by sires to the herd component, should herd and sire effects be correlated. Results and Discussion
Analysis of breeder herds. Results of an analysis of variance for the estimated breeding values of the 261 sons from the 19 breeder herds are in Table 1. Differences between breeder herds were not significant at the 0.05 level for either milk or fat. Estimated breeding values for these sons averaged 101 kg milk and 0.0% fat. Forty-five per cent of the sons had Each effect was assumed to be randomly and one parent bred in an outside herd, but 62% independently distributed with variances o'2b and of the sires of these sons were bred in the o-2e. Sires bred and tested in the same herd breeder herd. This suggested more of a tendency were not included, but it was assumed that bulls for the herds to represent separate breeding from different breeder herds were progeny units here than in Britain, where only 22% tested in herds of similar genetic merit. of the sires of such sons were from the breeder I n a further analysis, the 828 sons bred and herd (10). proved in different herds were divided into Components of variance for breeding values three groups. There were 282 sons originating associated with the sire's herd of origin acfrom breeder herds, 479 from nonbreeder herds, counted for only 2.7 and 2.2% of the variance and 67 from outside the United States. Differ- for milk yield and fat per cent in this small ences between these groups of herds were tested sample of herds. F o r interpretation of these on the basis of progeny tests of sons originating recall that the breeding values of the sires from them. were functions of regressed daughter averages; I n the second phase of the study, the herd thus, the genetic variance among them depends effects as defined for multiple (I) and single- on the correlation between the estimated breeding herd progenies ( I I ) were expressed as values and the actual breeding values, i.e., p2O-2g (1). For the estimated breeding values hi ~-- gi + mi (I) in the present study the correlation was nearly h'i ----- gi + nli (II) 0.7, and the component between breeder herds would need to be multiplied by two to give a where gi is the additively genetic deviation of the value equivalent to that expected if unregressed i th herd lactation records of the daughters had been used m i is the additional effect of management and in the analysis. I n addition, the differences other environmental factors for the i th herd. among the bull breeding herds in the analysis arise from the sample half of the genes which gi and mi were assumed uncorrelated and had males from the respective breeder herds transvariances O'2gh a n d O'2m . Use of 0.5 gi in (I) implies that since the sires are represented mitted to each of their progeny. The aforeacross herds, only the dams contribute to the mentioned variance components represent one genetic fraction of the differences among herds. quarter of the variance among average breeding The basis for the approach has been described values for males from the breeder herds. To (6,8). Certain bulls may have been used more present these on an individual record basis, heavily in specific herds, but the factorial analy- they further need to be multiplied by four. sis of herd and sire effects for multiheM prog- This gives 48,712 for milk yield and 0.0037 for enies would remove the potential contribution fat per cent as estimates of the genetic cornTABLE 1. Components of variance and per cent of total variance for sires with at least one parent bred in "breeder herds." Components
Per cent of total
Source
d/f
Milk
Test
Milk
Test
Breeder hems Sires/breeder herds Total
18 242 260
6,089 218,809 224,898
0.0005 0.0219 0.0224
2.7 97.3 100.0
2.2 97.8 100.0
JOURNAL
OF D A I R Y SCIENCE ~'OL. 53, NO. 7
MORILLO AND LEGATES
910
TABLE 2. Means and standard deviations for estimated breeding values by bullproducing groups.
Group
Number sires
Breeder herds Nonbreeder herds From outside U.S. Total
282 479 67 828
Milk (kg) Means 105 14 -- 38 40
ponents of the herd variance for these herds. The aforementioned values cannot be translated directly into the appropriate fraction of the herd differences which are genetic. Several of the breeder herds were on Advanced Registry test, and the data were not available to estimate the herd component for this sample of 19 herds. Nevertheless, when related to the herd component from the analysis of all single-herd progenies (Table 4), the genetic components were 12.4 and 18.7% of the herd components for milk and test. The 828 sons bred and proved in dit~erent herds were divided into three groups. Means and standard deviations for the unadjusted breeding values of these three groups are given in Table 2. The mean of the estimated breeding values for milk for the sires produced by breeder herds was 91 kg above the mean for other herds and 143 kg above the mean for sires bred outside the United States. Differences between the groups were significant at the 0.05 level for milk.
Multiple and single-herd progenies. Results of the analysis of variance for 5,409 progeny of sires whose offspring were in more than one herd are given in Table 3. Sires with less than ten progeny were not included in the analysis, to reduce the variation in family size and the nonorthogonality of the data. Thus, the sample of sires was representative not of the whole population but of the population of sires used in several herds and heavily enough to have produced a minfinum of ten tested daughters. Their progeny were in 358 of the original 442
Test (%)
SD
Mean
SD
526 525 594 532
0.00 0.00 0.02 0.00
0.161 0.179 0.183 0.173
herds. Herds involved were on test for a minimum of 6 consecutive years. Variance among herds accounted for 22.9% of the total variance for milk and 16.5% for fat per cent. While primary emphasis is on the herd components, these sire components are at the upper limit of those values reported in the literature. I n the subsequent analysis (Table 4) of the single-herd progenies, some inflation may have resulted from year-season effects. Negative sireby-herd interaction components suggest that such interactions are small, as numerous previous reports have indicated. Pertinent results from the analysis of variance for the data from single-herd progeny groups are given in Table 4. Removal of year-season effects reduced the residual components of variance for both milk and fat per cent for these two slightly different but overlapping samples of the data. From this analysis the herd component of variance accounted for 24.5% of the variance in milk yield and 18.5% of the variance in fat per cent. These components include more of the genetic differences among herds than those from the analysis in Table 3. Following the models and the assumptions previously given for the herd components for the multiple and single-herd progenies, the expectations of the herd components of variance are 0-2h :
1~ O-2gh .~- O-2111
z2~, = 0-2gh + zem and
Cr2gh =
(II)
~3 (¢r211' - - O"211)
Values of 0-2h and 0-2, for milk and fat per cent are given in Tables 3 and 4. Estimates of 0 . 2
TABLB 3. Components of variance and per cent of total variance for multiherd progenies. Components Source
d/f
Milk
Herds Sires Sire-by-herd Residual
357 202 1,218 3,631
366,542 166,770 --14,625 1,065,012
JOURNAL OF DAIRY SCIENCE VOL. 53, NO, 7
(I)
Per cent of total Test
0.0186 0.0173 --0.0040 0.0768
Milk
Test
22.9 16.5 10.4 15.3 ............ 66.7 68.2
GENETIC
DIFFERENCES
911
TABLE 4. Components of variance and per cent of total variance for single-herd progenies. Components
P e r cent of total
Source
d/f
Milk
Test
Milk
Test
Herds Sire/herd Year-season/sires/herds Residual
413 941 6,040 15,163
394,146 148,619 151,125 913,277
0.0200 0.0142 0.0053 0.0686
24.5 9.2 9.4 56.9
18.5 13.1 4.9 63.5
based on the above relationships were 36,805 for milk yield and 0.0018 for fat per cent. They represent 9.3 and 8.9% of the herd component of variance among single-herd progenies for these herds over the 8 years. The multiple-herd progenies included cows from 358 herds, whereas progeny from 414 herds were included in the single-herd progenies. Hence, the two samples of data should have been representative of the population of H I R bull proving herds. The estimate of 9.3% for the fraction of the herd variance in milk yield that is additively genetic is in reasonable agreement with most reported results, and it is on a much larger sample than most studies. E a r l y in the consideration of the heritability of herd differences, Lush and Straus (5) suggested that 6 to 7% of the herd differences in fat yield should be heritable, with an average expected relationship of 0.08 to 0.12 among herdmates. McGilliard (6) indicated that about one-third of the herd differences in fat yield were heritable in Jersey H I R data. However, from differences in the analyses his results are not directly comparable to those of the present study. Robertson and Rendel (11) computed the intra-sire regression of artificially sired daughters on their contemporary herd average for milk yield. Their results indicated a heritability of herd differences of 10%. Pirchner and Lush (8), with the same approach, estimated the heritability of herd differences to be 0.14 -4- 0.13 and 0.10 -----0.10 for samples of Jersey and Holstein data. Other population analyses (3,8) have confirmed these results. Two experimental studies whereby monozygotic twin pairs were split at birth between high-yielding and low-yielding farms have been conducted (2,12). By the regression of twin differences on herd differences, 24 ± 18% of the variance among herds was ascribed by Wiener (12) to genetic differences. I n the New Zealand study (2) monozygotic females from the high- and low-yielding herds also were brought to the Experiment Station and reared and milked there. Differences among herds, as
indicated by the milk yields of these two groups of heifers at the station, were nil. The regression of twin differences on herd differences for the monozygotic twins indicated that 7 ± 7% of the variation between herds was genetic (2). Estimates of the heritability of herd differences for fat per cent in these data are much below those reported by other investigators (2,10). Merely from the comparatively larger genetic influence on fat per cent within herds one might expect genetic differences between herds to be larger for test than milk yield. I n the analysis of sons from the breeder herds, the differences in fat per cent also were small. Breeders of l=ielstein-Friesian cattle in the United States have emphasized increasing fat content. F r o m 1930 to 1960 fat content for H I R herds has risen from 3.36 to 3.79%. Apparently, breeder herds and other H I R herds have shared closely this common goal. In conclusion, these results confirm other studies of the genetic differences among herds. Increased artificial insemination since these data were obtained should have reduced the genetic variance among these Holstein H I R herds even more. This being the case, the current adjustment for herd genetic level in U.S. Department of Agriculture Sire Summaries, comparable to 20% heritability of herd differences, appears too high. Positive bias to the Predicted Difference from this source would be expected to contribute disproportionately more to singleherd proofs. Herdmates for the daughters of bulls with single-herd proofs chosen for artificial insemination would be expected to be above the population mean. Hence, herd differences could make a larger contribution to the Predicted Difference in contrast to most multiherd proofs, where herdmates would not be expected to deviate much from the population mean. Even though the genetic fraction of herd differences is small, it is real. While the herd average would be more useful to indicate the level of environmental opportunity, it also should be given positive attention to predict breeding values of animals from different herds. JOURNAL OF DAIRY SCIENCE VOL. 53, NO. 7
912
~0RILLO AND LEGATES
References (1) Bereskin, B., and J. L. Lush. 1963. Considerations with environmental correlations among daughters in bull proofs. (Abstr.) J. Dairy Sci., 46: 627. (2) Brumby, P. J. 1961. The causes of differences in production between dairy herds. Animal Prod., 3: 277. (3) Freeman, A. E., and C. R. Henderson. 1959. Genetic structure of dairy cattle herds in terms of additive and dominance relationships. J. Dairy Sci., 42: 621. (4) Korkman, N. 1953. Versuch einer ver Gleichenden Nochkommenschaftsuntersuchung von Bullen die in Herden mit verschieden starken F u t t e r u n g wirken. Z. Tierziicht. Ziichtungsbiol., 61 : 375. (5) Lush, J. L., and F. S. Straus. 1942. The heritability of f a t production in dairy cattle. J. Dairy Sci., 25: 975. (6) McGilliard, L. D. 1952. Usefulness of the average in estimating breeding values of
JOURI~ALOF DAIBI' SOrENCEVOL. 53, NO. 7
(7) (8)
(9)
(10)
(11)
(12)
dairy cattle. Unpublished Ph.D. thesis, Iowa State University, Ames. Morillo, F. J., and J. E. Legates. 1970. Evaluation of progeny tests of dairy sires in single herds. J. Dairy Sei., 5 3 : A u g . Pirctmer, F., and J. L. Lush. 1959. Genetic and environmental portions of the variation among herds in butter f a t production. J. Dairy Sci., 42: 115. Robertson, A., and A. A. Asker. 1961. The genetic history and breeding structure of British-Friesian cattle. Emp. J. Exptl. Agr., 19 : 113. Robertson, A., and A. T. G. McArthur. 1955. Genetic differences between bull-breeding herds. Proe. British Soc. Animal Prod., 1955 : 94. Robertson, A., and J. M. Rendel. 1954. The performance of heifers got by artificial insemination. J. Agr. Sci., 44: 184. Wiener, Gerald. ]960. Factors influencing average milk yield of herds at two levels of production. Animal Prod., 2: 117.
Department of Animal Science North Carolina State University, Raleigh 27607 Abstract
Genetic differences among 442 HolsteinFriesian I:fIR herds that had been on test from March, 1952, to April, 1961, were examined. F i r s t lactations initiated at under 36 months of age for 37,890 individuals were studied by two approaches. I n the first, differences between bull breeder herds were compared by the progeny test evaluation of sires produced in a specific herd but progeny tested in another herd. Among 19 breeder herds that sold a large number of sons to other herds, four times the variance of breeding values of those sons, attributable to the herd in which they were bred, represented 12.4 and 18.7% of the herd component for milk yield and per cent fat. The mean genetic merit of 282 sons originating from these breeder herds was 92 kg o£ milk above the 479 sons from nonbreeder herds and 143 kg above the 67 sires originating from outside the United States. The second approach involved a comparison of the herd component of variance from multiherd progenies of sires with the herd component from single-herd progenies. The fraction of the herd variance for the population of 442 herds that was genetic was 9.3% for milk yield and 8.9% for f a t per cent. The results indicate that the genetic differences among these Holstein H I R herds are small but real, contributing about 10% of the variance among herd averages for milk. While the herd average would be more useful to correct for environmental differences among herds, it also should receive some positive attention for estimating genetic differences between individuals in different herds.
Received for publication November 14, 1969. 1 Paper no. 3023 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh. Computing services for this investigation were supported by Public Health Service Grant FR-00011. z Present address: Director of Research of the Ministry of Agriculture, Caracas, Venezuela.
Knowledge of the fraction of herd differences which are genetic is important in the formulation of sire evaluation procedures. Likewise, in choosing among females in different herds, as in the choice of dams of young sires, such genetic differences may warrant consideration. I n most attempts to examine the magnitude of the genetic differences between herds, existing production data have been utilized (4,6,9-11). Other studies of between-herd exchanges of monozygotic females have provided an experimental approach (2,10). Most of the results are in general agreement that genetic differences among herds within breeds for milk and f a t yields are small but real. This study was undertaken to determine the genetic differences among Holstein-Friesian bull breeding ("breeder") herds and also to examine the magnitude of the genetic differences among a population of 442 Holstein-Friesian HtIR herds. Data and Methods
Two approaches were used to examine the magnitude of genetic differences among groups of herds from a population of 442 Holstein I-IIl~ herds on test from March, 1952, to April, 1961. F i r s t lactations initiated at under 36 months of age for 37,890 individuals were studied. The first approach was that of Robertson and McArthur (10), in which herds were compared on the basis of estimated breeding values, unadjusted breeding values of Morillo and Legates (7), of sires produced in a specified herd but progeny tested in another herd. The second approach involved a comparison of the herd component of variance for multiherd progenies of sires with the herd component [from single-herd progenies as suggested by McGilliard (6)]. I n the first phase of the study, estimated breeding values for 828 sires bred aud proved in different herds were utilized. These breeding values were based on regressed deviations from the adjusted herdmate average for a minimum of 8 progeny in a herd (7). "Breeder" herds were herds having a minimum of 5 sons with a progeny test in a nonbreeder herd. A t least one of the parents of the sons had to be bred 908
909
G E N E T I C DIF:FERENCES
in the breeder herd. There were 19 breeder herds with 282 sons, of which 261 met the essential requirements. Breeding values for each sire (gik) expressed as deviations from the population mean were described and analyzed according to the following model : gik : bi -[- elk where bi is the effect of the i th breeder herd and eik is an effect peculiar to the k tu sire bred in the i th herd.
by sires to the herd component, should herd and sire effects be correlated. Results and Discussion
Analysis of breeder herds. Results of an analysis of variance for the estimated breeding values of the 261 sons from the 19 breeder herds are in Table 1. Differences between breeder herds were not significant at the 0.05 level for either milk or fat. Estimated breeding values for these sons averaged 101 kg milk and 0.0% fat. Forty-five per cent of the sons had Each effect was assumed to be randomly and one parent bred in an outside herd, but 62% independently distributed with variances o'2b and of the sires of these sons were bred in the o-2e. Sires bred and tested in the same herd breeder herd. This suggested more of a tendency were not included, but it was assumed that bulls for the herds to represent separate breeding from different breeder herds were progeny units here than in Britain, where only 22% tested in herds of similar genetic merit. of the sires of such sons were from the breeder I n a further analysis, the 828 sons bred and herd (10). proved in different herds were divided into Components of variance for breeding values three groups. There were 282 sons originating associated with the sire's herd of origin acfrom breeder herds, 479 from nonbreeder herds, counted for only 2.7 and 2.2% of the variance and 67 from outside the United States. Differ- for milk yield and fat per cent in this small ences between these groups of herds were tested sample of herds. F o r interpretation of these on the basis of progeny tests of sons originating recall that the breeding values of the sires from them. were functions of regressed daughter averages; I n the second phase of the study, the herd thus, the genetic variance among them depends effects as defined for multiple (I) and single- on the correlation between the estimated breeding herd progenies ( I I ) were expressed as values and the actual breeding values, i.e., p2O-2g (1). For the estimated breeding values hi ~-- gi + mi (I) in the present study the correlation was nearly h'i ----- gi + nli (II) 0.7, and the component between breeder herds would need to be multiplied by two to give a where gi is the additively genetic deviation of the value equivalent to that expected if unregressed i th herd lactation records of the daughters had been used m i is the additional effect of management and in the analysis. I n addition, the differences other environmental factors for the i th herd. among the bull breeding herds in the analysis arise from the sample half of the genes which gi and mi were assumed uncorrelated and had males from the respective breeder herds transvariances O'2gh a n d O'2m . Use of 0.5 gi in (I) implies that since the sires are represented mitted to each of their progeny. The aforeacross herds, only the dams contribute to the mentioned variance components represent one genetic fraction of the differences among herds. quarter of the variance among average breeding The basis for the approach has been described values for males from the breeder herds. To (6,8). Certain bulls may have been used more present these on an individual record basis, heavily in specific herds, but the factorial analy- they further need to be multiplied by four. sis of herd and sire effects for multiheM prog- This gives 48,712 for milk yield and 0.0037 for enies would remove the potential contribution fat per cent as estimates of the genetic cornTABLE 1. Components of variance and per cent of total variance for sires with at least one parent bred in "breeder herds." Components
Per cent of total
Source
d/f
Milk
Test
Milk
Test
Breeder hems Sires/breeder herds Total
18 242 260
6,089 218,809 224,898
0.0005 0.0219 0.0224
2.7 97.3 100.0
2.2 97.8 100.0
JOURNAL
OF D A I R Y SCIENCE ~'OL. 53, NO. 7
MORILLO AND LEGATES
910
TABLE 2. Means and standard deviations for estimated breeding values by bullproducing groups.
Group
Number sires
Breeder herds Nonbreeder herds From outside U.S. Total
282 479 67 828
Milk (kg) Means 105 14 -- 38 40
ponents of the herd variance for these herds. The aforementioned values cannot be translated directly into the appropriate fraction of the herd differences which are genetic. Several of the breeder herds were on Advanced Registry test, and the data were not available to estimate the herd component for this sample of 19 herds. Nevertheless, when related to the herd component from the analysis of all single-herd progenies (Table 4), the genetic components were 12.4 and 18.7% of the herd components for milk and test. The 828 sons bred and proved in dit~erent herds were divided into three groups. Means and standard deviations for the unadjusted breeding values of these three groups are given in Table 2. The mean of the estimated breeding values for milk for the sires produced by breeder herds was 91 kg above the mean for other herds and 143 kg above the mean for sires bred outside the United States. Differences between the groups were significant at the 0.05 level for milk.
Multiple and single-herd progenies. Results of the analysis of variance for 5,409 progeny of sires whose offspring were in more than one herd are given in Table 3. Sires with less than ten progeny were not included in the analysis, to reduce the variation in family size and the nonorthogonality of the data. Thus, the sample of sires was representative not of the whole population but of the population of sires used in several herds and heavily enough to have produced a minfinum of ten tested daughters. Their progeny were in 358 of the original 442
Test (%)
SD
Mean
SD
526 525 594 532
0.00 0.00 0.02 0.00
0.161 0.179 0.183 0.173
herds. Herds involved were on test for a minimum of 6 consecutive years. Variance among herds accounted for 22.9% of the total variance for milk and 16.5% for fat per cent. While primary emphasis is on the herd components, these sire components are at the upper limit of those values reported in the literature. I n the subsequent analysis (Table 4) of the single-herd progenies, some inflation may have resulted from year-season effects. Negative sireby-herd interaction components suggest that such interactions are small, as numerous previous reports have indicated. Pertinent results from the analysis of variance for the data from single-herd progeny groups are given in Table 4. Removal of year-season effects reduced the residual components of variance for both milk and fat per cent for these two slightly different but overlapping samples of the data. From this analysis the herd component of variance accounted for 24.5% of the variance in milk yield and 18.5% of the variance in fat per cent. These components include more of the genetic differences among herds than those from the analysis in Table 3. Following the models and the assumptions previously given for the herd components for the multiple and single-herd progenies, the expectations of the herd components of variance are 0-2h :
1~ O-2gh .~- O-2111
z2~, = 0-2gh + zem and
Cr2gh =
(II)
~3 (¢r211' - - O"211)
Values of 0-2h and 0-2, for milk and fat per cent are given in Tables 3 and 4. Estimates of 0 . 2
TABLB 3. Components of variance and per cent of total variance for multiherd progenies. Components Source
d/f
Milk
Herds Sires Sire-by-herd Residual
357 202 1,218 3,631
366,542 166,770 --14,625 1,065,012
JOURNAL OF DAIRY SCIENCE VOL. 53, NO, 7
(I)
Per cent of total Test
0.0186 0.0173 --0.0040 0.0768
Milk
Test
22.9 16.5 10.4 15.3 ............ 66.7 68.2
GENETIC
DIFFERENCES
911
TABLE 4. Components of variance and per cent of total variance for single-herd progenies. Components
P e r cent of total
Source
d/f
Milk
Test
Milk
Test
Herds Sire/herd Year-season/sires/herds Residual
413 941 6,040 15,163
394,146 148,619 151,125 913,277
0.0200 0.0142 0.0053 0.0686
24.5 9.2 9.4 56.9
18.5 13.1 4.9 63.5
based on the above relationships were 36,805 for milk yield and 0.0018 for fat per cent. They represent 9.3 and 8.9% of the herd component of variance among single-herd progenies for these herds over the 8 years. The multiple-herd progenies included cows from 358 herds, whereas progeny from 414 herds were included in the single-herd progenies. Hence, the two samples of data should have been representative of the population of H I R bull proving herds. The estimate of 9.3% for the fraction of the herd variance in milk yield that is additively genetic is in reasonable agreement with most reported results, and it is on a much larger sample than most studies. E a r l y in the consideration of the heritability of herd differences, Lush and Straus (5) suggested that 6 to 7% of the herd differences in fat yield should be heritable, with an average expected relationship of 0.08 to 0.12 among herdmates. McGilliard (6) indicated that about one-third of the herd differences in fat yield were heritable in Jersey H I R data. However, from differences in the analyses his results are not directly comparable to those of the present study. Robertson and Rendel (11) computed the intra-sire regression of artificially sired daughters on their contemporary herd average for milk yield. Their results indicated a heritability of herd differences of 10%. Pirchner and Lush (8), with the same approach, estimated the heritability of herd differences to be 0.14 -4- 0.13 and 0.10 -----0.10 for samples of Jersey and Holstein data. Other population analyses (3,8) have confirmed these results. Two experimental studies whereby monozygotic twin pairs were split at birth between high-yielding and low-yielding farms have been conducted (2,12). By the regression of twin differences on herd differences, 24 ± 18% of the variance among herds was ascribed by Wiener (12) to genetic differences. I n the New Zealand study (2) monozygotic females from the high- and low-yielding herds also were brought to the Experiment Station and reared and milked there. Differences among herds, as
indicated by the milk yields of these two groups of heifers at the station, were nil. The regression of twin differences on herd differences for the monozygotic twins indicated that 7 ± 7% of the variation between herds was genetic (2). Estimates of the heritability of herd differences for fat per cent in these data are much below those reported by other investigators (2,10). Merely from the comparatively larger genetic influence on fat per cent within herds one might expect genetic differences between herds to be larger for test than milk yield. I n the analysis of sons from the breeder herds, the differences in fat per cent also were small. Breeders of l=ielstein-Friesian cattle in the United States have emphasized increasing fat content. F r o m 1930 to 1960 fat content for H I R herds has risen from 3.36 to 3.79%. Apparently, breeder herds and other H I R herds have shared closely this common goal. In conclusion, these results confirm other studies of the genetic differences among herds. Increased artificial insemination since these data were obtained should have reduced the genetic variance among these Holstein H I R herds even more. This being the case, the current adjustment for herd genetic level in U.S. Department of Agriculture Sire Summaries, comparable to 20% heritability of herd differences, appears too high. Positive bias to the Predicted Difference from this source would be expected to contribute disproportionately more to singleherd proofs. Herdmates for the daughters of bulls with single-herd proofs chosen for artificial insemination would be expected to be above the population mean. Hence, herd differences could make a larger contribution to the Predicted Difference in contrast to most multiherd proofs, where herdmates would not be expected to deviate much from the population mean. Even though the genetic fraction of herd differences is small, it is real. While the herd average would be more useful to indicate the level of environmental opportunity, it also should be given positive attention to predict breeding values of animals from different herds. JOURNAL OF DAIRY SCIENCE VOL. 53, NO. 7
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References (1) Bereskin, B., and J. L. Lush. 1963. Considerations with environmental correlations among daughters in bull proofs. (Abstr.) J. Dairy Sci., 46: 627. (2) Brumby, P. J. 1961. The causes of differences in production between dairy herds. Animal Prod., 3: 277. (3) Freeman, A. E., and C. R. Henderson. 1959. Genetic structure of dairy cattle herds in terms of additive and dominance relationships. J. Dairy Sci., 42: 621. (4) Korkman, N. 1953. Versuch einer ver Gleichenden Nochkommenschaftsuntersuchung von Bullen die in Herden mit verschieden starken F u t t e r u n g wirken. Z. Tierziicht. Ziichtungsbiol., 61 : 375. (5) Lush, J. L., and F. S. Straus. 1942. The heritability of f a t production in dairy cattle. J. Dairy Sci., 25: 975. (6) McGilliard, L. D. 1952. Usefulness of the average in estimating breeding values of
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(9)
(10)
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(12)
dairy cattle. Unpublished Ph.D. thesis, Iowa State University, Ames. Morillo, F. J., and J. E. Legates. 1970. Evaluation of progeny tests of dairy sires in single herds. J. Dairy Sei., 5 3 : A u g . Pirctmer, F., and J. L. Lush. 1959. Genetic and environmental portions of the variation among herds in butter f a t production. J. Dairy Sci., 42: 115. Robertson, A., and A. A. Asker. 1961. The genetic history and breeding structure of British-Friesian cattle. Emp. J. Exptl. Agr., 19 : 113. Robertson, A., and A. T. G. McArthur. 1955. Genetic differences between bull-breeding herds. Proe. British Soc. Animal Prod., 1955 : 94. Robertson, A., and J. M. Rendel. 1954. The performance of heifers got by artificial insemination. J. Agr. Sci., 44: 184. Wiener, Gerald. ]960. Factors influencing average milk yield of herds at two levels of production. Animal Prod., 2: 117.