Body weight records from 90 to 450 days of age of Nellore animals from the Southeast and Center West of Brazil were used do estimate covariance structures of age dependent random effects for each region using random regression models. Covariance components of the regression coefficients were estimated by EMREML using the software REML90. The fixed effects of contemporary groups and additive genetic, additive maternal and permanent environment random effects were modeled by quadratic Legendre polynomials. The comparisons included structures of covariance and correlation of random effects, direct and maternal heritabitability and the ratio between genetic variances from different regions. The heritability, covariance and correlation structures showed similar patterns for both regions. Residual variance and permanent environment variances were smaller for Center West region as well as the maternal genetic additive from 150 to 400 days of age. Fixed effect trajectories in function of age of different contemporary groups showed different patterns, suggesting the necessity of specific set of regression coefficient estimates for each contemporary group. The maternal additive genetic variance showed higher heterogeneity between regions than the direct additive genetic variance.
beef cattle; covariance function; growth trajectory; random regression
