Estimate of genetic parameters for first lactation test-day records and total milk yield for Caracu cows

Genetic parameters for first lactation test-day milk yields and 305 day milk yield (M305) for Caracu cows were estimated. The test-day animal model included additive genetic effect as random and contemporary group and age of cow (quadratic regression) as fixed effects. Two contemporary groups were defined to explain variation, composed by year, week of test and paddock (gc1) or year, week of test and paddock (gc2). Variance components were estimated by Restricted Maximum Likelihood. Phenotypic, residual and genetic additive variances were higher at the beginning of lactation, however the genetic additive variances were proportionally smaller than the other variances. Heritability estimates ranged from 0.09 to 0.32 and were higher at the end of lactation, indicating larger genetic variability in this period. The genetic correlation (r(a)) among test-days were positive and decreased with the increase in lag between tests. Heritability for M305 was 0.27 and the r(a) between test days and M305 were positive and high, mainly for mid lactation. The results indicate greater genetic response in M305 through direct selection rather than by correlated response based on test-day milk yield selection.