Data consisting of 47.668 records of a Nellore-Angus crossbred population,raised in several regions of Brazil, from 1991 to 2001, were used to estimateheritability for post-weaning daily gain (ADG) and for scrotal circumferenceat yearling age (SCY) using REML. Genetic and phenotypic trends for ADG werealso estimated. The model used to estimate heritability and breeding values(BVs) for ADG included the fixed effects of breed composition (defined by thepercentage of contribution of the Nellore breed of the animal and his parents)and the contemporary group after weaning (herd, year/season of birth, sex andmanagement group) and the random additive genetic animal and residual effects.The same model, including the fixed effects of weight and age of the animalat yearling, as covariates, was used for SCY. The average ages at weaning andyearling were respectively 215 and 528 days. The heritability estimates forADG and SCY were 0.44 ± 0.02 and 0.22 ± 0.08, respectively. Theannual genetic trend for ADG decreased up to the year of 1996 and increasedthen on. The phenotypic trend was 9.4 g/day/year.
