Estimation of variances due to direct and maternal effects for growth traits of Nelore cattle.
Estimates of (co)variance components and genetic parameters were obtained for birth, 205-d, and 365-d weight for Nelore cattle in Brazil, using single and multiple-trait animal models. Data were from the Brazilian Zebu Breeders Association (ABCZ). Records of 27,549 calves sired by 587 bulls and raised on pasture in 57 herds were analyzed by restricted maximum likelihood fitting an animal model including direct and maternal genetic and permanent environmental effects. Single and multiple-trait analyses were carried out. Heritability estimates for direct effects were lower than previous values reported for the Nelore breed. The estimates for maternal genetic effects showed that the contribution of this component to the phenotypic variance of birth and weaning weight is not very high but is still present at yearling weight. Correlations between direct and maternal additive genetic effects were negative for all traits analyzed except for yearling weight in the single-trait analysis where the sign was positive but the magnitude was small (+.09). Genetic correlations between weaning and yearling weights were .74 (direct effect) and .84 (maternal effect). Permanent environmental and residual correlations among traits were also obtained.