UBC Theses and Dissertations
Estimation of genetic and environmental parameters of lifetime production traits and longevity in Holstein-Friesian cows Hoque, Mozzamel
This study was undertaken to evaluate the genetic and environmental aspects of lifetime production and longevity traits of dairy cattle. Canadian Record of Performance (ROP) data of 51,599 Holstein cows which first freshened from September, 1957 through February, 1966 were used, thus allowing cows time to complete 8 or more years of productive life by the end of 1974. These data included 23018 first lactation and 28581 multiple lactation cows from 2090 herds across Canada. The performance traits included were first lactation 305-day milk and fat yields; first lactation herd year deviation milk and fat yields; last lactation 305-day milk and fat yields; last lactation length; total lifetime milk and fat yields; milk and fat yields per day of productive life; age at culling; length of productive life; and number of lactations completed. Effects which might have a significant influence on traits under study were those of herd, year, season and year by season interaction. The covariables used were age at first calving for the first lactation cows, and age at first calving and calving interval for the multiple lactation cows. All effects were evaluated by least squares technique. Traits under study for first lactation cows were adjusted for age at first calving, and those for multiple lactation cows were adjusted for both age at first calving and calving interval; the resulting adjusted data were analyzed on within herd-year-season basis for estimation of genetic parameters. Heritability of each trait and phenotypic and genetic correlations among the traits were derived from paternal half-sib analysis using daughters of 138 sires of five groups according to sire's year of birth. Two separate sets of heritability estimates were obtained; estimates for (i) combined first and multiple lactation and (ii) multiple lactation cows were: first lactation 305-day milk .22 and .20, first lactation 305-day fat .25 and .25, first lactation herd-year deviation milk .22 and .20, first lactation herd-year deviation fat yield .24 and .25, last lactation 305-day milk .14 and .11, last lactation 305-day fat yield .16 and .14, last lactation length .06 and .07, lifetime milk .11 and .11, lifetime fat yield .12 and .12, milk per day of productive life .21 and .21, fat yield per day of productive life .25 and .28, culling age .10 and .09, length of productive life .10 and .09, and number of lactations .09 and .08, respectively. The average annual phenotypic and genetic trends were 72 kg and 31.2 kg, respectively for first lactation milk, 2.89 kg and .91 kg, respectively for first lactation fat. Genetic correlations of first lactation milk and fat yields with lifetime production and longevity traits ranged from .34 to .93 and .41 to .47, respectively for combined first and multiple lactation cows. The genetic correlations among measures of lifetime production ranged from .46 to .96 and among longevity traits were .99 or above for the same set of data. Separate estimates of genetic correlations based on multiple lactation cows only were all lower with higher standard error than the estimates obtained from combined set of data. The genetic correlations that were considered as having high predictive value were: first lactation milk correlated highly and positively with last lactation milk and milk per day of productive life; first lactation fat yield highly and positively correlated with last lactation fat yield and fat yield per day of productive life. Sires were ranked differently based on their expected breeding values (EBV) for production and longevity traits. The correlations of EBV's for first lactation yields with lifetime production and with longevity were positive (.31 to .89). The EBV's for first lactation milk and fat yields were found to be good predictors of EBV's for milk and fat yields per day of productive life, respectively. Genetic correlations of first lactation milk yield with lifetime milk yield (.56) and milk yield per day of productive life (.93) indicate that continued selection on first lactation milk production is an effective means of maximizing lifetime milk and milk per day of productive life. Significant positive genetic association of first lactation production with lifetime performance and longevity suggest that high producing heifers produce more milk and fat during their lifetime and remain in herds longer than lower producing heifers. These relations further indicate that the method of A.I. sire evaluation using daughters' first lactation level of production should result in proven bulls which will sire daughters which will produce well in later life and will remain in the herd longer.
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