Parâmetros e tendências genéticas para peso ao sobreano de animais Nelore criados no estado do Paraná, Brasil

Environmental effects and genetic parameters were estimated for weights at 365 and 550 days for Nellore cattle raised in the Parana State. Least Squared Means methodology, was used to estimate environmental effects. The model included as fixed effects year and month of birth calf, sex and age of dam at calving as a covariate and error as random effects. The variance components were estimated using an animal model considered as fixed effects contemporary group and age of dam. As random effect were composite of direct and maternal genetic additive effects and permanent environment. The genetic trends for direct and maternal effects were estimated by the regression of annual breeding value means on the animals’ year of birth. The heritability were 0.24±0.03 and 0.35±0.05 for direct genetic effect and 0.08±0.03 and 0.03±0.04 for maternal heritability for weights at 365 and 550 days, respectively. The genetic trends of the direct and maternal effects were 0.506 kg/year and -0.184 kg/year for weights at 365 days; and 0.712 kg/year and 0.187 kg/year for weights at 550 days. The results indicate the existence of adequate genetic variability to enable successful selection of breeding stock and realization of genetic gain.