Records of 19,458 Nellore breed animals, born from 1975 to 2002, from 8 herds participating in the Nellore Cattle Breeding Program (NCBP) were used to estimate (co)variance components, heritability and genetic correlations for birth weight, weaning weight, weight after yearling and at 2, 3 and 5 years of age. The restricted maximum likelihood method, with univariate, bivariate and multivariate analyses, was used. The models included the random additive genetic direct effect (animal) and fixed effects of age group and the linear and quadratic effects of calf age (except for the birth weight model) and age dam at calving. The random effect of permanent maternal environment was included in the analyses models for birth weight, weaning weight and yearling weight, and the random effect of maternal genetics only in the model for weaning weight. The heritability estimates, in multivariate analysis for weights at birth, weaning, yearling and at 2, 3 and 5 years of age were 0.25; 0.33; 0.34; 0.32; 0.33 and 0.35, respectively. The genetic correlations estimated between traits were positive and moderate to high in magnitude and tended to decrease with the increase in the distance between records, that indicated that selection for weight at any age will promote genetic change in weights at other ages including the female mature weight of the Nellore breed. The heritability estimates obtained in the multivariate analysis were high, especially at 3 and 5 years of age, suggesting better partition of genetic and environmental variances compared to uni and bivariate analyses but, high computer demands can still hinder its use in large databases.
beef cattle; body weight; genetic correlation; weight at maturity
