Genetic and phenotypic parameters of lifetime performance traits in Canadian Holsteins

Estimates of genetic and phenotypic parameters of lifetime performance traits and estimates of correlations between these and first lactation traits were obtained using multitrait mixed model and Restricted Maximum Likelihood (REML) methodologies, and accounting for all known additive genetic relationships amongst animals in sires pedigree. Part-lifetime performance traits, i.e. two-, three, and four-parity totals of yield and profit, were also included in the analysis. Data were on 82,835 Holstein cows, daughters of 703 sires, calving first between September 1979 and December 1984 in the herds enrolled in Quebec Dairy Herd Analysis Service (QDHAS). Lifetime performance records, however, continued through December 1989.Results of analysis indicated low estimates of heritability for lifetime performance traits, e.g., lifetime production and profit (.11$ sim$.13) and longevity (.07$ sim$.09). However, production per day of productive life traits had moderate heritability (.28$ sim$.32). Estimates of genetic and phenotypic parameters decreased from part-lifetime to total lifetime performance because residual variances increased at a greater rate compared to rate of increase in sire variances. Both genetic and phenotypic correlations amongst lifetime production, lifetime profit and longevity traits were very high and approached unity in all cases.Estimates of genetic and phenotypic correlations of first lactation production and profit traits with all measures of part and total lifetime performance were positive and high. These correlations decrease from part-lifetime to total lifetime performance due to part to whole relationships.Estimates of parameters of lifetime performance traits were mostly free of the effects of selection on milk production. Positive and high genetic correlation of first lactation milk yield with all lifetime performance traits indicated that selection on first lactation milk yield alone will improve all measures of lifetime performance. However, some consideration should be given to measures of reproduction and health which may help in improving the longevity of dairy cattle. (Abstract shortened by UMI.