Genetic Associations Betweeen Age at First Calving With Reproductive Efficiency and Neonatal Performance in Nellore Cattle

Age at first calving (AFC) is an important indicator of reproductive efficiency in beef cattle. Studies that simultaneously estimate genetic parameters for reproductive traits and neonatal performance in Zebu populations are still scarce. This study aimed to estimate variance components and genetic parameters for AFC, calving interval (CI), longevity (LONG), productive life (PL), neonatal vigor (VIG), and pre-weaning mortality (MT) in Nellore cattle. Data from 33,445 animals were analyzed, with a pedigree of 67,970 animals and genotypes of 2,623 individuals evaluated using a medium-density SNP panel. Single-trait linear and threshold animal models and two-trait models were fitted using Bayesian inference. The posterior heritability estimates were 0.19 ± 0.03 for AFC, 0.13 ± 0.02 for CI, 0.23 ± 0.03 for LONG, 0.17 ± 0.03 for PL, 0.31 ± 0.07 for VIG, and 0.14 ± 0.04 for MT, indicating low heritability for most traits, except for VIG, but with sufficient genetic variability to allow selection response. Posterior estimates of genetic correlation coefficients between AFC and the other traits were 0.35 ± 0.13 (AFC–CI), −0.27 ± 0.11 (AFC–LONG), −0.28 ± 0.15 (AFC–PL), −0.19 ± 0.16 (AFC–VIG), and 0.47 ± 0.13 (AFC–MT), indicating that females with a lower AFC tend to have shorter first calving intervals, remain productive in the herd for longer, and produce calves with lower mortality before four months of age. These results pointed out that management and selection strategies aimed at reducing age at first calving may contribute to more efficient and economically sustainable production systems.