This study aimed to evaluate the effect of the inclusion of genetic direct-maternal covariance on genetic parameters estimates and on ranking of breeding values (VG) for average daily gain from birth to weaning age (GMDND) and from weaning to 550 days of age (GMDDS) using records from 11,202 and 4,665 Angus animals respectively. Covariance components were estimated by restricted maximum likelihood method and for GMDND the model included the additive genetic direct, maternal, permanent environmental and residual random effects and the contemporary group at weaning and the covariables age of the cow at calving and age at weaning fixed effects. The model for GMDDS was similar, but included only the contemporary group at 550 days of age and the covariable age at 550 days as fixed effects. Both models included or not (assumed to be null) the genetic direct-maternal covariance. The estimated direct heritabilities for GMDND were 0.55 or 0.25 when the maternal-direct covariance was respectively fitted or not. Respective estimates for maternal heritability were 0.22 and 0.07. The estimated direct heritabilties for GMDDS including or not the genetic direct-maternal covariance were 0.22 and 0.21 respectively. The likelihood ratio test did not indicate significant diference between models for both traits. The Spearman rank correlations between sire VG from both models were 0.88 for GMDND and 0.99 for GMDDS suggesting that the inclusion of the maternal-direct genetic covariance is relevant only for GMDND.
average daily gain; heritability; maternal effect; Spearman correlation
