Genetic, phenotypic and environmental associations between reproduction traits and milk yield in the Brazilian Holstein breed

DFREML methodology and animal models were used to estimate heritabilities and genetic correlations between reproduction traits (age at first calving and first calving interval) and milk yield limited to 305 days in the first and second lactation. Original data file had 118,894 records on milk yield and reproductive traits of Brazilian Holstein females, calving between 1980 and 1992, in six States (ES, MG, PR, SC, SP and RS). Restrictions imposed to data structure were a minimum of four records for each herd-year-season of birth class and four daughters per sire, born in, at least, three different herds. Models included the fixed effects of herd-year-season and age of the animal. From bivariate animal models, heritabilitiy +/- standard error estimates were .35 +/- .01 and .05 +/- .01 For milk production in the first lactation and age at first calving, and .20 +/- .02 and .12 +/- .02 for milk production in the first lactation and first calving interval, respectively. From univariate animal model including dry period as covariate, milk production in the second lactation heritability estimate was .23 +/- .02. Genetic, phenotypic, and environmental correlation between milk production in the first lactation and age at first calving were -.65, .09 and .22, respectively. In the same order, correlations between milk production in the second lactation and first calving interval were .75, .21 and .11. Selection for milk production in the First lactation would reduce age at First calving and increase first calving interval.