GENETIC ASSOCIATION OF ANNUAL PRODUCTIVITY INDEX WITH REPRODUCTIVE AND GROWTH TRAITS IN BEEF CATTLE

The reproductive performance of the cow and its maternal ability affect the profitability of the cow-calf production systems. The objective of this study was to estimate components of (co) variance, heritability (h(2)) for the annual productivity index (PI), age at first calving (AFC), calving interval (CI) and weaning weight (WW), and genetic correlations (r(g)) among these traits, as well as the response to the selection in PI. The PI was calculated as the WW of the calf times 365, divided by the CI. The performance records used are from Brangus Negro (BN), Salers (SA) and Suizo Europeo (SE) cattle, coming from ranches in several Mexican states; the pedigree included 68 474 (BN), 15 594 (SA) and 187 294 (SE) animals. Univariate and bivariate analysis, which consider the animal model, were performed to estimate components of (co) variance and genetic parameters using the restricted maximum likelihood method, with the ASReml program. The direct h(2) for PI varied from 0.06 to 0.12, for AFC from 0.01 to 0.15, for CI from 0.07 to 0.12 and for WW from 0.15 to 0.23. The estimators of r(g) ranged from -0.09 to -0.76 for PI-AFC, from -0.90 to -0.93 for PI-CI and from 0.17 to 0.97 for PI-WW. The selection for WW resulted in higher PI correlated changes (between 0.06 and 1.53 kg cow(-1) year(-1)) than those obtained when using the direct selection for PI. The genetic correlations of PI with the other traits were favorable. The selection for WW, and then for PI, can genetically improve the annual productivity of cows.