Genetic trends in Nelore cattle selected for visual scores of conformation, precocity and musculature at weaning

The aims of this study were to estimate heritability coefficients and genetic trends for visual scores of conformation (C), finishing precocity (P) and musculature (M) in Nelore beef cattle. Variance components and heritability coefficients were estimated by restrict maximum likelihood and breeding values were predicted by an animal mixed model using data from 56,076 animals born between 1990 and 2002. Genetic trends for each trait were estimated by the regression of breeding values on animal birth year. Heritability estimates for direct effect of C, P and M were respectively 0.122 +/- 0.012, 0.153 +/- 0.012 and 0.124 +/- 0.012. In the same order of traits, maternal effect heritability estimates were respectively 0.043 +/- 0.010, 0.038 +/- 0.009 and 0.056 +/- 0.010. Direct genetic trend estimates were respectively 0.013, 0.022 and 0.018 score units per year for C, P and M, which represent 0.42, 0.67, and 0.60% of the phenotypic average. Maternal effect genetic trends were respectively -0.0020, -0.0010 and -0.0009 for C, P and M, which represent -0.07, -0.03, and -0.03% of the phenotypic average of the population.