Study of relations among age at first calving, average weight gains and weights from weaning to maturity in Nellore cattle

Data from 23,120 Nellore animals were used to estimate genetic parameters for age at first calving, average gains from weaning to yearling and from yearling to after yearling, weaning weight, yearling weight, after yearling weight and weight at 2 and 5 years of age. Animal models were fitted by Restricted Maximum likelihood Method. Estimate heritability for age at first calving, weaning to yearling weight gain, yearling to after yearling weight gain, weight at weaning, yearling weight, after yearling weight and weight from 2 to 5 years of age were 0.17 +/- 0.01; 0.23 +/- 0.03; 0.25 +/- 0.03; 0.28 +/- 0.02; 0.26 +/- 0.03; 0.30 +/- 0.03; 0.32 +/- 0.02 and 0.36 +/- 0.04, respectively. The genetic correlation estimates between age at first calving and weight traits ranged from -0.26 to -0.14. The genetic correlation estimates between age at first calving and average gains were also negative, but higher (-0.29 and -0.32). In general, these results indicate that selection for average gains will promote changes in age at first calving and female mature weight. Improvement in reproductive performance could be obtained with the inclusion of the age at first calving in the selection index.