Estimation of (co)variances for growth traits in Nellore cattle raised in the Humid Tropics of Brazil by random regression

Random regression models are currently used in genetic evaluation of beef cattle, because they allow changes in the mean and variance of the trait over time as well as estimation of (co) variances between any points along the growth curve. This study aimed to estimate (co)variances and genetic parameters for growth traits of Nelore cattle by random regression using models with heterogeneous and homogeneous residual variance. We utilized 23,278 weight records from birth to 550 days of age, from animals born between 1993 and 2010. The best-fitting model considered direct genetic, maternal genetic, permanent environmental animal and maternal permanent environmental effects, adjusted by fourth, third, sixth and fourth order polynomials, respectively. Heritability estimates for direct genetic effect increased from 120 to 450 days of age and then decreased at 550 days of age. Values at 120, 210, 365, 450 and 550 were 0.23, 0.23, 0.38, 0.52 and 0.43, respectively. Estimates of maternal heritability were low for all ages analyzed, ranging from 0.01 to 0.08. The genetic correlations were moderate to high, even at age extremes.