Reproductive performance of cows and genetic correlation with weight gains and principal components of traits used in selection of Nelore cattle

Abstract

The objectives of this study were to estimate heritability and genetic correlations for female traits (HR: heifer rebreeding; NC53: number of calves at 53 months of age; HP: heifer pregnancy at 18 months of age; AFC: age at first calving) and weight gains (BWG: from birth to weaning; WYG: from weaning to yearling) in Nelore cattle. Additionally, the relationship of these female traits with four principal components (PC) of predicted breeding values for traits used as selection criteria in this population was evaluated (i.e., weaning and postweaning weight gain, visual scores of conformation, finishing precocity and muscling, and scrotal circumference). The PC were obtained in previous analyses using phenotypic data from 600,132 animals. Low to moderate heritability were estimated for the females traits (HR: 0.12 ± 0.01; NC53: 0.13 ± 0.01; HP: 0.33 ± 0.02; AFC: 0.20 ± 0.01) and weight gains (BWG: 0.24 ± 0.01 and 0.14 ± 0.04 for direct and maternal effects; WYG: 0.21 ± 0.01). The genetic correlations between female traits were favorable, with positive and high estimates between HR, NC53 and HP (0.83 ± 0.03–0.94 ± 0.01) and negative between HR, NC53 and HP with AFC (-0.66 ± 0.02–−0.98 ± 0.01). Heifer rebreeding showed a moderate and negative genetic association with BWG and a positive association with WYG. The genetic association of NC53 with weight gains was positive and favorable (0.31 ± 0.03 with BWG and 0.42 ± 0.04 with WYG). Low genetic correlations were obtained between weight gains with HP and AFC. The first PC, with positive coefficients for all traits, showed a low and favorable genetic association with HP and AFC, but zero with HR and NC53. The second PC, which contrasted weaning and yearling traits, was genetically associated with HR (−0.17 ± 0.03). The third PC, related to early maturity, showed low and negative (favorable) genetic correlations with HR, NC53 and HP (−0.09 ± 0.01–−0.14 ± 0.02) and a positive genetic association with AFC (0.13 ± 0.01). The combination PC showed positive and low genetic correlations with HR and HP (0.12 ± 0.03 and 0.19 ± 0.02, respectively), and negative with NC53 and AFC (−0.08 ± 0.01 and −0.18 ± 0.02, respectively). In general, no relevant genetic antagonism was observed between female traits and weight gains; thus, simultaneous genetic improvements in these traits are possible. The selection based on principal components to achieve a particular breeding objective can provide low or no genetic gains in female traits. Our results thus reinforce the need to use reproductive traits measured directly in females as selection criteria to obtain improvements in sexual precocity and longevity of beef cows.