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Heritability of Age at First Calving
Heritability of Age at First Calving F. R. A L L A I R E and C. Y. LIN 1
Ohio State Universitv Columbus 43210 and Ohio Agricultural Research and Development Center Wooster 44691
variance among sires for age at first calving. They attributed the high heritability to confounding of sires with season of calving and to attempts by dairymen to obtain as many calvings as possible in autumn. Harville and Henderson (4) reported a heritability of .74 for Holstein cows while Gill and Allaire (2) reported .51. This note presents the effect of alternative analysis of variance models for the estimation of heritability of age at first calving.
ABSTRACT
High heritabilities of age at first calving reported by a number of researchers may be due to confounding of service sires and time heifers were bred. Heritabilities from paternal half-sister analyses of variance models which included the effects of period of birth were less than from models where these were not included. Heritabilities were .22 and .23 from data on Holstein cows in institutional herds in Ohio and herds in California.
DATA AND STATISTICAL MODELS
Data set A consisted of Dairy Herd Improvement records on 2312 Holstein cows in 38 herds in California. All cows had their first calving 1968 to 1969. Data set B consisted of records from 933 Holstein cows in eight herds managed by the Ohio Department of Corrections covering first calvings, 1955 to 1969. Both sets of data were available from other studies (2, 8). Genetic and phenotypic parameters were estimated by least squares analysis of variance program authored by Harvey (3). All statistical models were mixed models of a random sire effect (i.e., bull-progeny group mean) and alternative sets of fixed effects. All models for both sets of data included fixed effects of herds and of periods associated with time at first calving. The period effects were cross-classified into years and seasons. Alternative classifications for the time at the birth of the cow were compared for estimating heritability of age at first calving.
INTRODUCTION
The effects of ages at first calving on economic returns from dairy cows need to be determined to complete an economic evaluation of alternative reproductive managements. A more efficient deployment of resources by managers of dairy enterprises depends on quantification of economic returns expected from alternative managements as compared with alternative breeding and culling practices as well as other strategies of resource management. Should control of variation in age at first calving for economic or other purposes be sought, the genetic basis of variation both within and between stocks of dairy cattle will need to be assessed. Heritabilities for age at first calving have ranged from near zero to .74 (2, 4, 5, 6, 7, 10, 11). Some of these studies reported unexpectedly large heritabilities from data with relatively large numbers of observations. Hickman and Henderson (5) found a large
RESULTS A N D DISCUSSION
Received August 10, 1977. 1Journal Article No. 130-77 of the Ohio Agricultural Research and Development Center, Wooster, OH 44691. 2Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada. 1980 J Dairy Sci 63:171-173
Heritability estimates calculated under alternative models are in Table 1. In two data sets, large heritabilities occurred when the chronological period of birth was ignored. Heritabilities declined relative to the original statistical model when adjustment for period of birth was added to the model. Similar estimates
171
172
ALLAIRE AND LIN
TABLE 1. Classifications of period of birth of cows and heritability for age at first calving. Data set
Period of birth classification
No. half-sister groups
A: Lin and Allaire (8)
None Calendar month Month-year
457
1.05 1.03 .23
B: Gill and Allaire (2)
None 12 mo intervals 6 mo interval 3 mo interval
93
.51 .37
Heritability a
.26
.22
aThe standard error was .10 to .12 for data set A and .07 to .09 for data set B.
were o f the order .20 and occurred in b o t h data sets.
A partial c o n f o u n d i n g b e t w e e n period of birth and o c c u r r e n c e of particular groups o f bull-progeny seems to be indicated. Heritabilities changed in a similar manner u p o n only the addition o f period of birth to the original model. C o m m o n practices of heifer breeding and usage of service sires are h y p o t h e s i z e d as the basis o f a possible c o n f o u n d i n g o f the effects of period of birth and bull-progeny groups. Use of service sires in a sequential m a n n e r through t i m e tends to p r o d u c e progeny which are born in adjacent or proximal t i m e periods. Heifers b o r n during a particular period w o u l d tend to be mated concurrently. Therefore, sequential use of service sires w o u l d b e c o m e associated with any effects associated with period o f birth. Breeding practices to m a x i m i z e the proport i o n of cows calving in the a u t u m n season to take advantage o f favorable milk prices and the favorable effects o f all seasons on a total 10-mo lactation are well k n o w n . Efforts to concentrate heifer calvings in the a u t u m n w o u l d lead to increasing or decreasing the age o f first calving d e p e n d i n g on the m o n t h o f birth. F r e q u e n c y distributions presented by Miller (9) indicate most heifers 30 m o of age at calving were born during F e b r u a r y and March while m o s t heifers 24 m o of age were born in August and September. The c o m b i n a t i o n of sequential use o f service sires, particularly likely for natural service in heifer lots or pasture breeding, and practices to c o n c e n t r a t e a u t u m n calving w o u l d c o n t r i b u t e to c o n f o u n d i n g sire and period of birth effects Journal of Dairy Science Vol. 63, No. 1, 1980
on the trait age at first calving. A large decline occurred in heritability from the m o d e l partitioning t i m e of birth into sequential m o n t h l y intervals (i.e., m o n t h - y e a r ) relative to the m o d e l with t i m e classified according to calendar months. The effect o f each calendar m o n t h w o u l d n o t uncover effects associated with breeding sequences in bull usage which are not repeated on an annual basis. The gradual decline in estimates with a shortening of sequence times in data set B supports this hypothesis. No significant changes occurred in genetic and p h e n o t y p i c estimates for traits o t h e r than age at first calving in b o t h sets of data. O t h e r traits included: milk, fat, fat percent, days open, calculated profit, and length o f herdlife. The stability o f the heritabilities indicated period of birth was not associated with bull-progeny groups for o t h e r traits (2, 8).
REFERENCES
1 Gill, G. S., and F. R. Allaire. 1976. Relationship of age at first calving, days open, days dry, and herdlife to a profit function for dairy cattle. J. Dairy Sci. 59:1131. 2 Gill, G. S., and F. R. Allaire. 1976. Genetic and phenotypic parameters for a profit function and selection method for optimizing pofit in dairy cattle. J. Dairy Sci. 59:1325. 3 Harvey, W. R. 1970. Estimation of variance and covariance components in a mixed model. Biometrics 26:485. 4 Harville, D. A., and C. R. Henderson. 1966. Interrelationship among age, body weight, and production traits during first lactation of dairy cattle. J. Dairy Sci. 49:1254. 5 Hickrnan, C. G., and C. R. Henderson. 1955. Components of the relationship between level of
TECHNICAL NOTE production and rate of maturity in dairy cattle. J. Dairy Sci. 38:883. 6 Larson, C. J., A. B. Chapman, and L. E. Casida. 1951. Butterfat production per day of life as a criterion o f selection in dairy cattle. J. Dairy Sci. 34:1163. 7 Lee, A. J. 1976. Relationship between milk yield and age at calving in first lactation. J. Dairy Sci. 59:1794. 8 Lin, C. Y., and F. R. Allaire. 1978. Efficiency o f selection on milk yield up to a fixed age. J. Dairy
173
Sci. 61:489. 9 Miller, P. D. 1973. A recent study o f age adjustment. J. Dairy Sci. 56:952. 10 Schaeffer, L. R., and C. R. Henderson. 1972. Effects of days dry and days open on Holstein-milk production. J. Dairy Sci. 55:107. 11 Silva, H. M., C. J. Wilcox, and R. B. Becket. 1976. Age at first parturition and productive life span o f Florida dairy cows. Page 129 in Proc. 71st Annu. Mtg. Am. Dairy Sci. Assoc.; North Carolina State Univ., Raleigh.
Journal of Dairy Science Vol. 63, No. 1, 1980
Ohio State Universitv Columbus 43210 and Ohio Agricultural Research and Development Center Wooster 44691
variance among sires for age at first calving. They attributed the high heritability to confounding of sires with season of calving and to attempts by dairymen to obtain as many calvings as possible in autumn. Harville and Henderson (4) reported a heritability of .74 for Holstein cows while Gill and Allaire (2) reported .51. This note presents the effect of alternative analysis of variance models for the estimation of heritability of age at first calving.
ABSTRACT
High heritabilities of age at first calving reported by a number of researchers may be due to confounding of service sires and time heifers were bred. Heritabilities from paternal half-sister analyses of variance models which included the effects of period of birth were less than from models where these were not included. Heritabilities were .22 and .23 from data on Holstein cows in institutional herds in Ohio and herds in California.
DATA AND STATISTICAL MODELS
Data set A consisted of Dairy Herd Improvement records on 2312 Holstein cows in 38 herds in California. All cows had their first calving 1968 to 1969. Data set B consisted of records from 933 Holstein cows in eight herds managed by the Ohio Department of Corrections covering first calvings, 1955 to 1969. Both sets of data were available from other studies (2, 8). Genetic and phenotypic parameters were estimated by least squares analysis of variance program authored by Harvey (3). All statistical models were mixed models of a random sire effect (i.e., bull-progeny group mean) and alternative sets of fixed effects. All models for both sets of data included fixed effects of herds and of periods associated with time at first calving. The period effects were cross-classified into years and seasons. Alternative classifications for the time at the birth of the cow were compared for estimating heritability of age at first calving.
INTRODUCTION
The effects of ages at first calving on economic returns from dairy cows need to be determined to complete an economic evaluation of alternative reproductive managements. A more efficient deployment of resources by managers of dairy enterprises depends on quantification of economic returns expected from alternative managements as compared with alternative breeding and culling practices as well as other strategies of resource management. Should control of variation in age at first calving for economic or other purposes be sought, the genetic basis of variation both within and between stocks of dairy cattle will need to be assessed. Heritabilities for age at first calving have ranged from near zero to .74 (2, 4, 5, 6, 7, 10, 11). Some of these studies reported unexpectedly large heritabilities from data with relatively large numbers of observations. Hickman and Henderson (5) found a large
RESULTS A N D DISCUSSION
Received August 10, 1977. 1Journal Article No. 130-77 of the Ohio Agricultural Research and Development Center, Wooster, OH 44691. 2Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada. 1980 J Dairy Sci 63:171-173
Heritability estimates calculated under alternative models are in Table 1. In two data sets, large heritabilities occurred when the chronological period of birth was ignored. Heritabilities declined relative to the original statistical model when adjustment for period of birth was added to the model. Similar estimates
171
172
ALLAIRE AND LIN
TABLE 1. Classifications of period of birth of cows and heritability for age at first calving. Data set
Period of birth classification
No. half-sister groups
A: Lin and Allaire (8)
None Calendar month Month-year
457
1.05 1.03 .23
B: Gill and Allaire (2)
None 12 mo intervals 6 mo interval 3 mo interval
93
.51 .37
Heritability a
.26
.22
aThe standard error was .10 to .12 for data set A and .07 to .09 for data set B.
were o f the order .20 and occurred in b o t h data sets.
A partial c o n f o u n d i n g b e t w e e n period of birth and o c c u r r e n c e of particular groups o f bull-progeny seems to be indicated. Heritabilities changed in a similar manner u p o n only the addition o f period of birth to the original model. C o m m o n practices of heifer breeding and usage of service sires are h y p o t h e s i z e d as the basis o f a possible c o n f o u n d i n g o f the effects of period of birth and bull-progeny groups. Use of service sires in a sequential m a n n e r through t i m e tends to p r o d u c e progeny which are born in adjacent or proximal t i m e periods. Heifers b o r n during a particular period w o u l d tend to be mated concurrently. Therefore, sequential use of service sires w o u l d b e c o m e associated with any effects associated with period o f birth. Breeding practices to m a x i m i z e the proport i o n of cows calving in the a u t u m n season to take advantage o f favorable milk prices and the favorable effects o f all seasons on a total 10-mo lactation are well k n o w n . Efforts to concentrate heifer calvings in the a u t u m n w o u l d lead to increasing or decreasing the age o f first calving d e p e n d i n g on the m o n t h o f birth. F r e q u e n c y distributions presented by Miller (9) indicate most heifers 30 m o of age at calving were born during F e b r u a r y and March while m o s t heifers 24 m o of age were born in August and September. The c o m b i n a t i o n of sequential use o f service sires, particularly likely for natural service in heifer lots or pasture breeding, and practices to c o n c e n t r a t e a u t u m n calving w o u l d c o n t r i b u t e to c o n f o u n d i n g sire and period of birth effects Journal of Dairy Science Vol. 63, No. 1, 1980
on the trait age at first calving. A large decline occurred in heritability from the m o d e l partitioning t i m e of birth into sequential m o n t h l y intervals (i.e., m o n t h - y e a r ) relative to the m o d e l with t i m e classified according to calendar months. The effect o f each calendar m o n t h w o u l d n o t uncover effects associated with breeding sequences in bull usage which are not repeated on an annual basis. The gradual decline in estimates with a shortening of sequence times in data set B supports this hypothesis. No significant changes occurred in genetic and p h e n o t y p i c estimates for traits o t h e r than age at first calving in b o t h sets of data. O t h e r traits included: milk, fat, fat percent, days open, calculated profit, and length o f herdlife. The stability o f the heritabilities indicated period of birth was not associated with bull-progeny groups for o t h e r traits (2, 8).
REFERENCES
1 Gill, G. S., and F. R. Allaire. 1976. Relationship of age at first calving, days open, days dry, and herdlife to a profit function for dairy cattle. J. Dairy Sci. 59:1131. 2 Gill, G. S., and F. R. Allaire. 1976. Genetic and phenotypic parameters for a profit function and selection method for optimizing pofit in dairy cattle. J. Dairy Sci. 59:1325. 3 Harvey, W. R. 1970. Estimation of variance and covariance components in a mixed model. Biometrics 26:485. 4 Harville, D. A., and C. R. Henderson. 1966. Interrelationship among age, body weight, and production traits during first lactation of dairy cattle. J. Dairy Sci. 49:1254. 5 Hickrnan, C. G., and C. R. Henderson. 1955. Components of the relationship between level of
TECHNICAL NOTE production and rate of maturity in dairy cattle. J. Dairy Sci. 38:883. 6 Larson, C. J., A. B. Chapman, and L. E. Casida. 1951. Butterfat production per day of life as a criterion o f selection in dairy cattle. J. Dairy Sci. 34:1163. 7 Lee, A. J. 1976. Relationship between milk yield and age at calving in first lactation. J. Dairy Sci. 59:1794. 8 Lin, C. Y., and F. R. Allaire. 1978. Efficiency o f selection on milk yield up to a fixed age. J. Dairy
173
Sci. 61:489. 9 Miller, P. D. 1973. A recent study o f age adjustment. J. Dairy Sci. 56:952. 10 Schaeffer, L. R., and C. R. Henderson. 1972. Effects of days dry and days open on Holstein-milk production. J. Dairy Sci. 55:107. 11 Silva, H. M., C. J. Wilcox, and R. B. Becket. 1976. Age at first parturition and productive life span o f Florida dairy cows. Page 129 in Proc. 71st Annu. Mtg. Am. Dairy Sci. Assoc.; North Carolina State Univ., Raleigh.
Journal of Dairy Science Vol. 63, No. 1, 1980