Asociación entre características reproductivas y producción de leche, en novillas mestizas

Abstract

This research was carried out in heifers from a crisscrossing program between theredHolstein and Brahman breeds, inVenezuela. (Co)variance components were estimated and the relationship between milk yield (P305), age (AGE1) and fertility at first service (FERT1) in virgin heifers was investigated. The analysis methodology was restricted maximum likelihood (REML),under a multivariate animal model. The mixed model included: the random effect of the animal; and the fixed effects of racial group, year-seasons of the event occurrence; for P305, the duration of lactation was also included as a covariate in quadratic form. Heritabilities were: 0.498 ± 0.022; 0.436 ± 0.020 and 0.024 ± 0.008, for P305, AGE1and FERT1 respectively. Genetic correlations between: P305-AGE1; P305-FERT1 and AGE1-FERT1, were: -0.281±0.040; 0.238 ± 0.117 and -0.076 ± 0.123, these results suggest a favorable genetic association between P305-AGE1, as well as,between P305-FERT1. Weighted regression analysis of the averages breeding valueson years, showed an improvement in P305 of 10.85 kg/year and a reduction of -0.1150 month/year in AGE1 representing 0.60 and 0.41% of the population means for those traits (p < 0.01);the annual genetic change for FERT1 was not significant (p > 0.05). The phenotypic changes in P305 and AGE1were not significant (p > 0.05). It is concluded that there is no genetic antagonism between P305 and FERT1 and that it is possible to reduce AGE1 for decreasing the costs for generating replacement heifers, improving the rate of genetic change in P305.