Evaluation of the productive and reproductive performance of sexual precocity at different ages in Nellore heifers.

This study aimed to investigate the differences between productive and reproductive performance traits of sexually precocious and non-sexually precocious Nellore heifers and to evaluate the genetic correlation of sexual precocity with traits of economic importance. For this purpose, 300,000 Nellore heifers were evaluated for reproductive traits: heifer pregnancy (HP) at 14 (HP), 18 (HP), and 24 (HP) months; heifer rebreeding (HR); number of progenies up to 53 months (NP); and probability of the cow remaining in the herd until 76 months with at least 3 progenies (Stay). The growth-related traits evaluated included female yearling weight (YW); average daily gain from weaning to yearling (ADG); weight at maturity (MW); weaning weight of first progeny (WW); and female visual scores at yearling for conformation (Conf), precocity (Prec) and muscling (Musc). The effects of female YW and ADG in six categories on HP, HP, and HP were analyzed using Generalized linear mixed models (GLMM). Furthermore, a linear mixed model was used to evaluate the impact of HP on WW, MW, and reproductive performance (NP and Stay). Genetic correlations of HP evaluated in different months with growth and reproductive traits were estimated using a bivariate animal model. Precocious heifers (HP) were lighter for YW and MW but had greater ADG than HP and HP. The probability for HP, HP, and HP increased as the classes of YW and ADG increased. However, heifers weighing more than 326 kg had a slight reduction in the probability of becoming pregnant at HP and HP. Precocious heifers (HP and HP) produced their first progeny by 3 % lighter than HP, although they had a greater NP. Precocious heifers at 18 months (HP) were 3 % and 6.8 % more likely to remain in the herd than HP and HP heifers, respectively. Genetic correlations between growth traits (WW, YW, ADG and MW) and heifer pregnancy (HP, HP, and HP) ranged from weak (r = 0.27 ± 0.05) to moderate (r = -0.47 ± 0.07). The genetic correlation between HR and HP was stronger for HP (0.75) against HP (0.58) and HP (0.64). Although, the genetic correlation between NP and Stay with HP was higher (r = 0.53 and 0.45) than those observed for HP (r = 0.46 and 0.38) and HP (r = 0.35 and 0.39). The genetic correlation estimates between HP and visual scores were moderate and favorable for HP. Selecting HP is beneficial for production systems because it increases the NP during the productive life without compromising heifer productivity or reproductive performance. However, attention should be given to improving the HR of heifers who become pregnant early.