Genetic and phenotypic parameters of lifetime production traits in Holstein cows

Canadian Record of Performance data of 51,599 Holstein cows freshened first between 1958 and 1965 were used to evaluate genetic and environmental aspects of production and longevity traits. Traits were adjusted for age at first 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: first lactation 305 day milk .22 (.03); first lactation 305 day fat yield .25 (.03); first lactation herd-year deviation milk .22 (.02); first lactation herd-year deviation fat yield .24 (.03); last lactation 305 day milk .14 (.02); last lactation 305 day fat yield .16 (.02); last lactation length .06 (.01); lifetime milk .11 (.02); lifetime fat yield .12 (.02); milk per day of productive life .21 (.02); fat per day of productive life .25 (.03); culling age .10 (.01); length of productive life .10 (.01); and number of lactations completed .09 (.01). Genetic correlations of first lactation yield with lifetime production ranged from .34 to .93 and with longevity traits from .41 to .47. Genetic correlations between lifetime production traits ranged from .43 to .96 and between longevity traits were greater than or equal to .99. Genetic correlations of first lactation milk with lifetime milk (.56) and milk per day of productive life (.93) indicate that continued selection on first lactation milk is an effective means of maximizing lifetime milk and milk per day of productive life.