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 (HP₁₄), 18 (HP₁₈), and 24 (HP₂₄) months; heifer rebreeding (HR); number of progenies up to 53 months (NP₅₃); 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_W-Y); weight at maturity (MW); weaning weight of first progeny (WW_prog); and female visual scores at yearling for conformation (Conf), precocity (Prec) and muscling (Musc). The effects of female YW and ADG_W-Y in six categories on HP₁₄, HP₁₈, and HP₂₄ were analyzed using Generalized linear mixed models (GLMM). Furthermore, a linear mixed model was used to evaluate the impact of HP on WW_prog, MW, and reproductive performance (NP₅₃ and Stay). Genetic correlations of HP evaluated in different months with growth and reproductive traits were estimated using a bivariate animal model. Precocious heifers (HP₁₄) were lighter for YW and MW but had greater ADG_W-Y than HP₁₈ and HP₂₄. The probability for HP₁₄, HP₁₈, and HP₂₄ increased as the classes of YW and ADG_W-Y increased. However, heifers weighing more than 326 kg had a slight reduction in the probability of becoming pregnant at HP₁₄ and HP₁₈. Precocious heifers (HP₁₄ and HP₁₈) produced their first progeny by 3 % lighter than HP₂₄, although they had a greater NP₅₃. Precocious heifers at 18 months (HP₁₈) were 3 % and 6.8 % more likely to remain in the herd than HP₁₄ and HP₂₄ heifers, respectively. Genetic correlations between growth traits (WW, YW, ADG_W-Y, and MW) and heifer pregnancy (HP₁₄, HP₁₈, and HP₂₄) ranged from weak (r_g = 0.27 ± 0.05) to moderate (r_g = −0.47 ± 0.07). The genetic correlation between HR and HP was stronger for HP₂₄ (0.75) against HP₁₄ (0.58) and HP₁₈ (0.64). Although, the genetic correlation between NP₅₃ and Stay with HP₁₄ was higher (r_g = 0.53 and 0.45) than those observed for HP₁₈ (r_g = 0.46 and 0.38) and HP₂₄ (r_g = 0.35 and 0.39). The genetic correlation estimates between HP and visual scores were moderate and favorable for HP₁₄. Selecting HP₁₄ is beneficial for production systems because it increases the NP₅₃ 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.