Variance components and breeding values for post weaning growth traits of Nellore cattle, from different statistical models

Data from the Genetic Improvement Program of the Nellore Breed of Genetic Department-USP were used to estimate genetic parameters and breeding values for weights at 365 (P365) and 455 (P455) days of age. Four animal models were used to obtain REML estimates of genetic parameters aiming to evaluate the effect of the inclusion of a random maternal genetic effect and a permanent environmental effect on variance component estimates. The model 1 included genetic and residual random effects; model 2 and model 3 were based on model 1 but included permanent environmental (2) and maternal genetic (3) effects; model 4 included genetic, maternal and permanent environmental effects. The heritability estimates for P365 were 0.48, 0.32, 0.28 and 0.27 using models 1, 2, 3 and 4, respectively. For P455, the values were 0.48, 0.38, 0.35 e 0.34 with the same models. The results suggest that maternal effects may be of slight importance for yearling weight but of no importance for P455.