Genetic and environmental effects on Nellore cattle growth in Paraiba

Records on 6,674 Nellore cattle weight, born from 1975 to 1990 in two farms located in Paraiba State were used to study environmental effects and to estimate genetic parameters for average daily gains from birth to 205 days, from 205 to 365 days and from 365 to 550 days. The SAS(R) program was used to study the environmental effects. The model included the random effect of sire and the fixed effects of year-month-sex, farm and age of the cow at calving as linear and quadratic covariate. The (co)variance components used to estimate direct and maternal heritabilities were obtained by Derivative Free Restricted Maximum Likelihood using the MTDFREML program, under an animal model. All effects used were significant, but the farm effect for pre-weaning daily gain. The estimated means for average daily gains were 0.575+/-0.089, 0.231+/-0.114 and 0.283+/-0.110 kg for pre-weaning daily gain, daily gain from 205 to 365 days and daily gain from 365 to 550 days of age, respectively. The heritabilities estimated for direct effect were 0.12, 0.42 and 0.21 and for maternal effect were 0.29, 0.00 and 0.00. The estimates of heritability show that selection based on daily gain from 205 days to yearling could allow considerable genetic gain.