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Genetic Relationship between Birth Weight and Adult Weight in Holsteins
G e n e t i c R e l a t i o n s h i p B e t w e e n Birth W e i g h t and A d u l t W e i g h t in Holsteins R. C. LAMB and B. O. BARKER Agricultural Research Service U. S. Department of Agriculture Logan, UT 84322 and Department of Dairy Science Utah State University, Logan 84322
calves and fewer calving complications. This practice, however, seriously limits potential selection for milk yield. From a practical standpoint, we need to select dairy bulls that sire calves that are small at birth but that may develop into average-size cows. Boyd and Hafs (2) found that some bulls sired smaller than average calves for their breed, but these authors did not study the size of the calves at maturity. Martin et al. (10, 11) found correlations less than .40 between birth weight and weight gains to 1 yr of age in dairy cattle. Matthews and Fohrman (12, 13) reported correlations between birth weight and weight at 7 yr of age of .21 for Holsteins and .33 for Jerseys. These results imply that there is only a small relationship between birth weight and size at maturity. Genetic correlations between birth weight and adult weights in dairy cattle could not be found. This research evaluated effects of sire and herd on birth weight and subsequent weight at calving, determined heritability of birth and calving weights, and measured phenotypic and genetic relationships between birth weight of Holstein heifer calves and size of these same animals as adults.
ABSTRACT
Records of body weight for 1026 Holstein females from two herds included birth weight and all available subsequent calving weights for the first six parities. Birth weight differed between herds and between sires within herds. Years also differed; however, partial nesting of sires within years could account for part of this. Month of birth had no influence on birth weight. Calving weights differed between herds only at the second and fifth parities. Calving weights differed between sires within herds for the first five parities. Intraherd correlations between the birth weight of a heifer calf and later calving weights for her first six parities ranged from .22 to .34. Correlations between the birth weight of a calf and the average birth weight of her paternal half-sibs were .37 and .48 in the two herds. Heritabilities for birth and calving weights were of the same magnitude within herds but differed between herds. Genetic correlations between birth and adult weights were above .5 in one herd but erratic in the other herd, INTRODUCTION
Birth weight of calves is affected by breed (2, 9, 11, 16), sex (11, 18, 19, 20), sire (2, 3, 18, 19), and dam (2, 5, 6, 8, 15, 17, 18, 19, 20). Some workers have reported influences of herd, month, and year on birth weight (8) whereas others have reported month and year were insignificant (3, 15, 18, 19). In 1971, 7.2% of all artifically inseminated dairy cattle in the U. S. were bred to bulls of beef breeds (7) presumably to obtain smaller
Received September 3, 1974.
MATERIALS AND METHODS
Body weight data were obtained over 21 yr (1940 to 1960)on 373 Holstein-Friesian females at the USDA Field Station, Huntley, MT, and over 16 yr (1955 to 1970) on 653 HolsteinFriesian females at the Utah State University Dairy Farm, Logan, UT. Body weights included birth weight taken within 24 h of birth and calving weights taken within 3 days after parturition for each of the available first six lactations of these same animals. Only animals with a recorded birth weight and at least one calving weight were included.
724
BIRTH AND ADULT WEIGHTS
725
TABLE 1. Mean birth and calving weights by parity and herd.
Parity
BWb
All 1 2 3 4 5 6
43.6 43.5 43.7 44.0 44.1 44.5 44.8
USDAa CWc ... 538 622 677 701 722 739
USUa Nd
BWb
CWc
Nd
373 367 286 172 118 73 38
41.6 41.5 42.0 41.8 41.9 42.0 43.0
536 608 679 721 752 754
653 597 395 199 113 83 36
au. S. Department of Agriculture; Utah State University. bMean birth weight in kg for cows having a calving weight at the parity listed. CMean calving weight in kg. dNumber of animals. The 1026 animals were sired by 95 bulls. First calving weights were missing for 62 cows, but second or later calving weights were available and included. Culling reduced the number of cows for each successive parity. Mean birth weight was determined for all 1026 animals. Mean birth weight and mean calving weight were determined for each parity group. A least squares analysis of variance was performed on each parity group to test for differences in birth and calving weights between herds and between sires within herds. Least squares analysis was also performed on the 1026 birth weight observations to test for differences due to herds, sires within herds, and month and year of birth. Intraherd correlations were determined between birth weight, calving weights, and number of lactations completed. Linear regressions of birth weight on years, calving weight on birth weight, and number of complete lactations on birth weight were also determined. Heritabilities of birth and calving weights were calculated within herds as four times the intrasire correlation among paternal half-sibs. Genetic correlations between birth weight and subsequent calving weights in the same animal were estimated from the intrasire variance and covariance components (1). Only sire groups with three or more daughters per sire were used.
RESULTS AND DISCUSSION Mean birth weights are listed by herd in Table 1. Weight at birth for individual calves
ranged from 25 to 62 kg. The standard deviation for birth weight was 4.9 kg for both herds. Birth weights were heavier in the USDA herd (P < .01) than in the USU herd. Differences in birth weights were also highly significant (P < .01) between sires within herds; these significant differences support the results of Boyd and Hafs (2). Birth weight by years and regression of birth weight on years were calculated for both herds (Fig. 1). Birth weight varied between years in both herds (P < .01). Sires were nested partly within years, and this nesting may account for much of the variation between years. The regression shows an increase (P < .01) of .12 kg per year in average birth weight in the USDA herd. The slight regression in the USU herd was not significantly different from zero and, thus, indicated no definite linear trend in average birth weight. Month of birth had no significant influence on birth weight for either herd.
-T"
43
~_,z~--/--V V V I-LI 4ll/
STF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1940 45 50 55
/ \ A
60
usu
-
A
~Z_xc_ ~---
65
70
YEARS
FIG. 1. Average birth weight by years within herds. Journal of Dairy Science Vol. 58, No. 5
726
LAMB AND BARKER
Standard deviations for calving weights were similar for the two herds; they ranged from 54 to 75 kg for the various parities (Table 1). Differences in calving weight were highly significant (P < .01) between sires within herds from the first through the fifty parity. Although average weight of cows in the two herds was the same at first calving, second parity cows were heavier (P < .05) in the USDA herd than in the USU herd. Cows in the USU herd then outgrew those at Huntley and were heavier (P < .05) at fifth calving. Differences between herds at other calvings were not significant. Cows in both herds increased in weight with each successive parity; the largest increases were up to fourth parity. Average calving weight appeared to stabilize by fifth or sixth parity. Animals were heavier at birth in the USDA herd but were heaviest as adults in the USU herd. Data from both herds suggest that calves of average or larger size at birth may on the average complete more lactations than smaller calves. In the USDA herd, calves weighing < 41, 41 to 45, and > 45 kg (113, 146, and 114 calves) averaged 2.6, 2.9, and 3.0 lactations. In the USU herd, calves weighing < 39, 39 to 43, and > 43 kg (182, 251, and 220 calves) averaged 2.2, 2.4, and 2.5 lactations. However, correlations between number of lactations completed and birth weight were less than .1. Intraherd correlations and regressions between birth and later calving weights are in Table 2. The correlations, though small ( < .35), were generally statistically significant and indicated a positive relationship between the birth
weight of a calf and her later calving weights. These correlations were of the same magnitude as those found by Matthews and Fohrman (12, 13). Regressions of calving weight on an animal's own birth weight were also significantly larger than zero. However, weight increased less than 4.5 kg in mature weight for each kg increase in birth weight. When these regressions and the standard deviation of 5 kg for birth weight were used, two thirds of the mature cows were predicted within a 45 kg weight range for any given lactation. The range of weights was actually much higher than this; thus, other factors influence adult size. High significant (P < .01)correlations of .48 in the USDA herd and .37 in the USU herd between birth weight of a calf and the average birth weights of her paternal half-sibs support the conclusion that the sire influences birth weight. Correlations between calving weight and average birth weight of a sire group were .28 to .32 for the first through fourth calvings in the USDA herd (P < .01). Only first calving weight was correlated (.09) with average birth weight of a sire group in the USU herd. Although significant, these correlations were too small to assume any important relationship between a sire and the adult weight of his offspring. Heritability estimates (Table 3) were of the same magnitude for calving weights as for birth weight. Although estimates were higher in the USDA herd, standard errors were relatively large because of small numbers, particularly for
TABLE 2. Phenotypic correlations and regressions between birth weight and calving weight in the same animal. Birth weight Calvingweight
r
1st 2nd 3rd 4th 5th 6th
.30** .33** .29** .29** .10 .28
a
USDAa b 3.72** 4.41"* 3.48** 3.44** 1.10 4.17
b U. S. Department of Agrxculture; Utah State University. Number of observations. *Different from O, P < .05. **Different from O, P < .01. Journal of Dairy Science Vol. 58, No. 5
Nb
r
367 286 172 118 73 38
.26** .22** .12 .23** .34** .24
USUb b 2.83** 2.79** 1.61 3.17"* 4.41"* 3.38
Nb 579 395 199 113 83 36
727
BIRTH AND ADULT WEIGHTS TABLE 3. Heritabilities and genetic correlations. USDAa
USUa
Weight
hb
rc
Birth 1st calving 2nd calving 3rd calving 4th calving 5th calving 6th calving
.75 ± .40 d .82 ± .39 .70 ± .45
.66 ± .22 .76 ± .16
.59
.62 +- .28
.35 +- .75 ...e .48 ± 1.O2
.69 ±
.64 ± .32 ...e ...e
hb
r e
.35 -+ .32 .34-+ .34 .33 ± .40 .44 ± .58 .33 ± .82 .31 ± 1.15 ...e
.10 -.32 .01 .39 -.46 -.08
+- .28 +- .32 ± .40 ± .43 -+ .43 -+ .91
a
bU. S. Department of Agriculture; Utah State University. Heritability. c • • dGenetlc correlanon between birth weight and weight at indicated calving. Indicates standard error. eNo estimate.
later parities. Heritabilities o f b i r t h weights were as large as or larger t h a n e s t i m a t e s in t h e literature (5, 9, 14) and larger t h a n for m a n y p r o d u c t i o n traits in dairy cattle. G e n e t i c c o r r e l a t i o n s (Table 3) were quite erratic and d i f f e r e d c o n s i d e r a b l y b e t w e e n herds, p r o b a b l y due t o sampling b e c a u s e o f the limited n u m b e r of sire groups and t h e small n u m b e r o f d a u g h t e r s per sire. Genetic correlations in t h e U S D A h e r d were larger t h a n t h e p h e n o t y p i c c o r r e l a t i o n s b e t w e e n b i r t h and adult w e i g h t s ; t h e increase in birth w e i g h t o f calves over t i m e may have b e e n a result o f s o m e selection for larger m a t u r e size. The m a g n i t u d e o f t h e s e genetic e s t i m a t e s indicate t h a t larger or smaller size, e i t h e r at birth or m a t u r i t y , can be selected f o r and t h a t selection f o r one will t e n d t o change t h e o t h e r . However, u n d e r the p r o p e r set o f i n d e p e n d e n t culling levels or the a p p r o p r i a t e index, l o w e r birth weight and higher m a t u r e w e i g h t likely could be selected.
REFERENCES
1. Becker, W. A. 1967. Manual of procedures in quantitative genetics. Washington State University Press. Pullman, WA. 2. Boyd, L. J., and H. D. Hafs. 1965. Body size of calves from Holstein dams and sired by Holstein or Angus bulls. J. Dairy Sci. 48:1236. 3. Davis, H. P. 1957. Influences of season of the year and sire upon the birth weight and six- and twelve-month gains in weight for Holstein females. J. Dairy Sci. 40:631. (Abstr.) 4. Draper, N., and H. Smith. 1966. Applied regression analysis. Wiley, New York.
5. Everett, R. W., and W. T. Magee. 1965. Maternal ability and genetic ability of birth weight and gestation length. J. Dairy Sci. 48:957. 6. Foote, W. D., W. J. Tyler, and L. E. Casida. 1959. Effect of some genetic and maternal environmental variations on birth weight and gestation length in Holstein cattle. J. Dairy Sci. 42:305. 7. King, G. J., F. N. Dickinson, C. A. Rampendahl, A. H. Kienast, and M. K. Dixon. 1972. U. S. Department of Agriculture Dairy Herd Improvement Letter 40:4. June. 8. Koonce, K. L., and E. U. Dillard. 1967. Some environmental effects on birth weight and gestation length in Hereford cattle. J. Anita. Sci. 26:205. 9. Legault, C. R., and R. W. Touchberry. 1962. Heritability of birth weight and its relationship with production in dairy cattle. J. Dairy Sci. 45:1226. 10. Martin, T. G., N. L. Jacohson, and C. G. Homeger. 1954. Effects of season of birth, sex, birth weight, and diet on growth of dairy calves. J. Anita. Sci. 13:7. 11. Martin, T. G., N. L. Jacobson, and L. D. McGilliard. 1962. Factors related to weight gain of dairy calves. J. Dairy Sci. 45:886. 12. Matthews, C. A., and M. H. Fohrman. 1954. Beltsville growth standards for Jersey cattle. U. S. Dep. Agr. Tech. Bull. 1098. 13. Matthews, C. A., and M. H. Fohrman. 1954. Beltsville growth standards for Holstein cattle. U. S. Dep. Agr. Tech. Bull. 1099. 14. Plum, M., H. Andersen, and L. A. Swiger. 1965. Heritability estimates of gestation length and birth weight in Holstein-Friesian cattle and their use in selection indexes. J. Dairy Sci. 48:1672. 15. Stone, E. J., E. B. Morgan, J. E. Johnston, and J. B. Frye, Jr. 1958. A preliminary analysis: birth weights of Holstein and Jersey female calves born in southern Louisiana. J. Dairy Sci. 41:343. (Abstr.) Journal of Dairy Science Vol. 58, No. 5
728
LAMB AND BARKER
16. Touchberry, R. W., and B. Bereskin. 1966. Crossbreeding dairy cattle. I. Some effects of crossbreeding on the birth weight and gestation period of dairy cattle. J. Dairy Sci. 49:287. 17. Touchberry, R. W., and K. A. Tabler. 1954. Variations in the birth weights of purebred and crossbred Holstein and Guernsey calves. J. Anita. Sci. 13:10. 18. Tyler, W. J., A. B. Chapman, and G. E. Dickerson.
Journal of Dairy Science Vol. 58, No. 5
1947. Sources of variation in the birth weight of Holstein-Friesian calves. J. Dairy Sci. 30:483. 19. Wilcox, C. J., and D. K. Roy. 1968. Factors affecting birth weights and gestation lengths in Jersey cattle. J. Dairy Sci. 51:629. (Abstr.) 20. Wilcox, C. J., and J. A. Staffa. 1964. Effects of uterine horn pregnant, age of dam, and sex of calf on birth weights and gestation lengths of dairy cattle. J. Dairy Sci. 47:346. (Abstr.)
calves and fewer calving complications. This practice, however, seriously limits potential selection for milk yield. From a practical standpoint, we need to select dairy bulls that sire calves that are small at birth but that may develop into average-size cows. Boyd and Hafs (2) found that some bulls sired smaller than average calves for their breed, but these authors did not study the size of the calves at maturity. Martin et al. (10, 11) found correlations less than .40 between birth weight and weight gains to 1 yr of age in dairy cattle. Matthews and Fohrman (12, 13) reported correlations between birth weight and weight at 7 yr of age of .21 for Holsteins and .33 for Jerseys. These results imply that there is only a small relationship between birth weight and size at maturity. Genetic correlations between birth weight and adult weights in dairy cattle could not be found. This research evaluated effects of sire and herd on birth weight and subsequent weight at calving, determined heritability of birth and calving weights, and measured phenotypic and genetic relationships between birth weight of Holstein heifer calves and size of these same animals as adults.
ABSTRACT
Records of body weight for 1026 Holstein females from two herds included birth weight and all available subsequent calving weights for the first six parities. Birth weight differed between herds and between sires within herds. Years also differed; however, partial nesting of sires within years could account for part of this. Month of birth had no influence on birth weight. Calving weights differed between herds only at the second and fifth parities. Calving weights differed between sires within herds for the first five parities. Intraherd correlations between the birth weight of a heifer calf and later calving weights for her first six parities ranged from .22 to .34. Correlations between the birth weight of a calf and the average birth weight of her paternal half-sibs were .37 and .48 in the two herds. Heritabilities for birth and calving weights were of the same magnitude within herds but differed between herds. Genetic correlations between birth and adult weights were above .5 in one herd but erratic in the other herd, INTRODUCTION
Birth weight of calves is affected by breed (2, 9, 11, 16), sex (11, 18, 19, 20), sire (2, 3, 18, 19), and dam (2, 5, 6, 8, 15, 17, 18, 19, 20). Some workers have reported influences of herd, month, and year on birth weight (8) whereas others have reported month and year were insignificant (3, 15, 18, 19). In 1971, 7.2% of all artifically inseminated dairy cattle in the U. S. were bred to bulls of beef breeds (7) presumably to obtain smaller
Received September 3, 1974.
MATERIALS AND METHODS
Body weight data were obtained over 21 yr (1940 to 1960)on 373 Holstein-Friesian females at the USDA Field Station, Huntley, MT, and over 16 yr (1955 to 1970) on 653 HolsteinFriesian females at the Utah State University Dairy Farm, Logan, UT. Body weights included birth weight taken within 24 h of birth and calving weights taken within 3 days after parturition for each of the available first six lactations of these same animals. Only animals with a recorded birth weight and at least one calving weight were included.
724
BIRTH AND ADULT WEIGHTS
725
TABLE 1. Mean birth and calving weights by parity and herd.
Parity
BWb
All 1 2 3 4 5 6
43.6 43.5 43.7 44.0 44.1 44.5 44.8
USDAa CWc ... 538 622 677 701 722 739
USUa Nd
BWb
CWc
Nd
373 367 286 172 118 73 38
41.6 41.5 42.0 41.8 41.9 42.0 43.0
536 608 679 721 752 754
653 597 395 199 113 83 36
au. S. Department of Agriculture; Utah State University. bMean birth weight in kg for cows having a calving weight at the parity listed. CMean calving weight in kg. dNumber of animals. The 1026 animals were sired by 95 bulls. First calving weights were missing for 62 cows, but second or later calving weights were available and included. Culling reduced the number of cows for each successive parity. Mean birth weight was determined for all 1026 animals. Mean birth weight and mean calving weight were determined for each parity group. A least squares analysis of variance was performed on each parity group to test for differences in birth and calving weights between herds and between sires within herds. Least squares analysis was also performed on the 1026 birth weight observations to test for differences due to herds, sires within herds, and month and year of birth. Intraherd correlations were determined between birth weight, calving weights, and number of lactations completed. Linear regressions of birth weight on years, calving weight on birth weight, and number of complete lactations on birth weight were also determined. Heritabilities of birth and calving weights were calculated within herds as four times the intrasire correlation among paternal half-sibs. Genetic correlations between birth weight and subsequent calving weights in the same animal were estimated from the intrasire variance and covariance components (1). Only sire groups with three or more daughters per sire were used.
RESULTS AND DISCUSSION Mean birth weights are listed by herd in Table 1. Weight at birth for individual calves
ranged from 25 to 62 kg. The standard deviation for birth weight was 4.9 kg for both herds. Birth weights were heavier in the USDA herd (P < .01) than in the USU herd. Differences in birth weights were also highly significant (P < .01) between sires within herds; these significant differences support the results of Boyd and Hafs (2). Birth weight by years and regression of birth weight on years were calculated for both herds (Fig. 1). Birth weight varied between years in both herds (P < .01). Sires were nested partly within years, and this nesting may account for much of the variation between years. The regression shows an increase (P < .01) of .12 kg per year in average birth weight in the USDA herd. The slight regression in the USU herd was not significantly different from zero and, thus, indicated no definite linear trend in average birth weight. Month of birth had no significant influence on birth weight for either herd.
-T"
43
~_,z~--/--V V V I-LI 4ll/
STF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1940 45 50 55
/ \ A
60
usu
-
A
~Z_xc_ ~---
65
70
YEARS
FIG. 1. Average birth weight by years within herds. Journal of Dairy Science Vol. 58, No. 5
726
LAMB AND BARKER
Standard deviations for calving weights were similar for the two herds; they ranged from 54 to 75 kg for the various parities (Table 1). Differences in calving weight were highly significant (P < .01) between sires within herds from the first through the fifty parity. Although average weight of cows in the two herds was the same at first calving, second parity cows were heavier (P < .05) in the USDA herd than in the USU herd. Cows in the USU herd then outgrew those at Huntley and were heavier (P < .05) at fifth calving. Differences between herds at other calvings were not significant. Cows in both herds increased in weight with each successive parity; the largest increases were up to fourth parity. Average calving weight appeared to stabilize by fifth or sixth parity. Animals were heavier at birth in the USDA herd but were heaviest as adults in the USU herd. Data from both herds suggest that calves of average or larger size at birth may on the average complete more lactations than smaller calves. In the USDA herd, calves weighing < 41, 41 to 45, and > 45 kg (113, 146, and 114 calves) averaged 2.6, 2.9, and 3.0 lactations. In the USU herd, calves weighing < 39, 39 to 43, and > 43 kg (182, 251, and 220 calves) averaged 2.2, 2.4, and 2.5 lactations. However, correlations between number of lactations completed and birth weight were less than .1. Intraherd correlations and regressions between birth and later calving weights are in Table 2. The correlations, though small ( < .35), were generally statistically significant and indicated a positive relationship between the birth
weight of a calf and her later calving weights. These correlations were of the same magnitude as those found by Matthews and Fohrman (12, 13). Regressions of calving weight on an animal's own birth weight were also significantly larger than zero. However, weight increased less than 4.5 kg in mature weight for each kg increase in birth weight. When these regressions and the standard deviation of 5 kg for birth weight were used, two thirds of the mature cows were predicted within a 45 kg weight range for any given lactation. The range of weights was actually much higher than this; thus, other factors influence adult size. High significant (P < .01)correlations of .48 in the USDA herd and .37 in the USU herd between birth weight of a calf and the average birth weights of her paternal half-sibs support the conclusion that the sire influences birth weight. Correlations between calving weight and average birth weight of a sire group were .28 to .32 for the first through fourth calvings in the USDA herd (P < .01). Only first calving weight was correlated (.09) with average birth weight of a sire group in the USU herd. Although significant, these correlations were too small to assume any important relationship between a sire and the adult weight of his offspring. Heritability estimates (Table 3) were of the same magnitude for calving weights as for birth weight. Although estimates were higher in the USDA herd, standard errors were relatively large because of small numbers, particularly for
TABLE 2. Phenotypic correlations and regressions between birth weight and calving weight in the same animal. Birth weight Calvingweight
r
1st 2nd 3rd 4th 5th 6th
.30** .33** .29** .29** .10 .28
a
USDAa b 3.72** 4.41"* 3.48** 3.44** 1.10 4.17
b U. S. Department of Agrxculture; Utah State University. Number of observations. *Different from O, P < .05. **Different from O, P < .01. Journal of Dairy Science Vol. 58, No. 5
Nb
r
367 286 172 118 73 38
.26** .22** .12 .23** .34** .24
USUb b 2.83** 2.79** 1.61 3.17"* 4.41"* 3.38
Nb 579 395 199 113 83 36
727
BIRTH AND ADULT WEIGHTS TABLE 3. Heritabilities and genetic correlations. USDAa
USUa
Weight
hb
rc
Birth 1st calving 2nd calving 3rd calving 4th calving 5th calving 6th calving
.75 ± .40 d .82 ± .39 .70 ± .45
.66 ± .22 .76 ± .16
.59
.62 +- .28
.35 +- .75 ...e .48 ± 1.O2
.69 ±
.64 ± .32 ...e ...e
hb
r e
.35 -+ .32 .34-+ .34 .33 ± .40 .44 ± .58 .33 ± .82 .31 ± 1.15 ...e
.10 -.32 .01 .39 -.46 -.08
+- .28 +- .32 ± .40 ± .43 -+ .43 -+ .91
a
bU. S. Department of Agriculture; Utah State University. Heritability. c • • dGenetlc correlanon between birth weight and weight at indicated calving. Indicates standard error. eNo estimate.
later parities. Heritabilities o f b i r t h weights were as large as or larger t h a n e s t i m a t e s in t h e literature (5, 9, 14) and larger t h a n for m a n y p r o d u c t i o n traits in dairy cattle. G e n e t i c c o r r e l a t i o n s (Table 3) were quite erratic and d i f f e r e d c o n s i d e r a b l y b e t w e e n herds, p r o b a b l y due t o sampling b e c a u s e o f the limited n u m b e r of sire groups and t h e small n u m b e r o f d a u g h t e r s per sire. Genetic correlations in t h e U S D A h e r d were larger t h a n t h e p h e n o t y p i c c o r r e l a t i o n s b e t w e e n b i r t h and adult w e i g h t s ; t h e increase in birth w e i g h t o f calves over t i m e may have b e e n a result o f s o m e selection for larger m a t u r e size. The m a g n i t u d e o f t h e s e genetic e s t i m a t e s indicate t h a t larger or smaller size, e i t h e r at birth or m a t u r i t y , can be selected f o r and t h a t selection f o r one will t e n d t o change t h e o t h e r . However, u n d e r the p r o p e r set o f i n d e p e n d e n t culling levels or the a p p r o p r i a t e index, l o w e r birth weight and higher m a t u r e w e i g h t likely could be selected.
REFERENCES
1. Becker, W. A. 1967. Manual of procedures in quantitative genetics. Washington State University Press. Pullman, WA. 2. Boyd, L. J., and H. D. Hafs. 1965. Body size of calves from Holstein dams and sired by Holstein or Angus bulls. J. Dairy Sci. 48:1236. 3. Davis, H. P. 1957. Influences of season of the year and sire upon the birth weight and six- and twelve-month gains in weight for Holstein females. J. Dairy Sci. 40:631. (Abstr.) 4. Draper, N., and H. Smith. 1966. Applied regression analysis. Wiley, New York.
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16. Touchberry, R. W., and B. Bereskin. 1966. Crossbreeding dairy cattle. I. Some effects of crossbreeding on the birth weight and gestation period of dairy cattle. J. Dairy Sci. 49:287. 17. Touchberry, R. W., and K. A. Tabler. 1954. Variations in the birth weights of purebred and crossbred Holstein and Guernsey calves. J. Anita. Sci. 13:10. 18. Tyler, W. J., A. B. Chapman, and G. E. Dickerson.
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1947. Sources of variation in the birth weight of Holstein-Friesian calves. J. Dairy Sci. 30:483. 19. Wilcox, C. J., and D. K. Roy. 1968. Factors affecting birth weights and gestation lengths in Jersey cattle. J. Dairy Sci. 51:629. (Abstr.) 20. Wilcox, C. J., and J. A. Staffa. 1964. Effects of uterine horn pregnant, age of dam, and sex of calf on birth weights and gestation lengths of dairy cattle. J. Dairy Sci. 47:346. (Abstr.)