Heritability estimates of age at first calving in Nelore cattle

The aim of this study was to verify estimated heritability for age at first calving (AFC) and age at first calving with non-calved females (AFC_P). Heifers were born from 1995 to 2014 and were from Nelore Qualitas Breeding Program. Records of 23,489 and 44,717 heifers were considered in the analysis for AFC and AFC_P, respectively. Non-calved cows received a predicted phenotype according to higher observed record within contemporary group (CG). The CGs were formed on the basis of herd, year and season of birth, weaning management group and postweaning management group. Poorly representative CGs with fewer than 10 animals and fewer than two sires were eliminated. The pedigree file included all animals with an observation plus their parents and grandparents and a total of 75,595 animals in the relationship matrix. The AFC and AFC_P traits were analyzed by the use of animal model in single-trait analysis. Random effects of genetic additive and residual and fixed effect of contemporary group were included in the model. The variance components were estimated using WOMBAT program according to the AIREML algorithm. The estimates of heritability were 0.10 ? 0.01 and 0.05 ? 0.00 for AFC and AFC_P, respectively. The results of heritability estimates showed that inclusion of non-calved female records in the analysis did not improve the identification of genetic differences between the studied animals.