Correlations between first lactation and lifetime performance traits of Canadian Holsteins.

Data on 82,835 Holstein cows, daughters of 703 sires and with first calvings from 1979 to 1984 in 2384 herds enrolled in Quebec Dairy Herd Analysis Service, were analyzed for relationships of first lactation traits with traits for partial and total lifetime performance using multitrait REML methodology and a linear mixed model. Effects of herd-year-season, age at first calving, and proven sires were considered to be fixed, and effects of young sires and residuals were considered to be random. All known additive genetic relationships among sires were accounted for in construction of the relationship matrix. Individual lactation records were precorrected for the fixed effect of year and month of calving before lifetime totals were calculated. Each cow was given at least a 5-yr opportunity for production. All genetic and phenotypic correlations were positive except correlations of first lactation percentage traits. Correlations with partial lifetime performance were highest. Genetically, first lactation milk yield was highly correlated with most measures of lifetime performance, .64 to .92; correlations with measures of longevity were relatively smaller. Given high positive genetic correlations, selection singly on first lactation milk yield will improve all measures of lifetime performance; however, some measure of longevity should be considered in selection programs of dairy cattle.