Impact of the phenotypic and genetic merit of growth, reproduction, and carcass traits on sexual precocity in Nelore heifers using multivariate analysis techniques

The aim was to verify, using multivariate techniques, which growth and carcass traits, and their variations throughout the reproductive season, are related to the sexual precocity of Nellore heifers. Data from ANCP (Ribeirão Preto, SP) and Bacuri farm (Barretos, SP) were used from heifers exposed to reproduction between 10 and 14 months of age, recording pregnancy status (pregnant and empty). Phenotypic values and Genomic Estimated Breeding Values (GEBV) for growth, reproduction, and carcass traits were evaluated. Variance and discriminant multivariate analyses were performed to assess the effect of variables on early pregnancy. Significant statistical differences (P < 0.05) were observed between the groups of pregnant and empty females for live weight at the end of mating season (WF: 363.63±36.21 and 352.57±35.35 kg), rump fat thickness (RFT: 6.62±2.27 and 4.43±1.71 mm), and rump fat thickness gain during mating season (G:RFT: 0.04±0.01 and 0.02±0.02 mm). These traits showed significant discriminant power for early pregnancy. The GEBVs for probability of early calving and age at first calving were significant (P < 0.05) for discriminating early pregnancy, as well as the GEBV for rib eye area. Thus, heavier heifers with greater carcass finish at the end of mating season and genetic merit for sexual precocity determine the success of early pregnancy. Therefore, environmental conditions leading to greater fat deposition in the carcass and genetic selection for traits related to sexual precocity can be used as strategies to reduce puberty age and increase the rate of early pregnancy.