Genetic and Phenotypic Parameters of Lifetime Production Traits in Holstein Cows

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Abstract
Canadian Record of Performance data of 51,599 Holstein cows freshened 1st between 1958 and 1965 were used to evaluate genetic and environmental aspects of production and longevity traits. Traits were adjusted for age at 1st calving and for average and last calving intervals by partial regression coefficients derived from these data. Heritabilities and phenotypic and genetic correlations then were estimated from paternal half-sister analyses of 138 sires representing 5 genetic time-trend groups. Within herd-year-season, heritabilities (and standard errors) were given. Genetic correlations of first lactation yield with lifetime production ranged from 0.34-0.93 and with longevity traits from 0.41-0.47. Genetic correlations between lifetime production traits ranged from 0.43-0.96 and between longevity traits were .gtoreq. 0.99. Genetic correlations of 1st lactation milk with lifetime milk (0.56) as well as milk per day of productive life (0.93), indicate that continued selection on 1st lactation milk is an effective means of maximizing lifetime milk and milk/day of productive life.