Parâmetros genéticos para peso da vaca à desmama do bezerro

Abstract

The selection of weight traits in young animals leads to greater weight in adult animals, which in turn generates animals with a higher maintenance cost, thus making the production process more expensive, especially with respect to the matrices that remain in the herd for a longer time. In this sense, the present study aimed to estimate genetic parameters for weight of cow at calf weaning in Nelore cattle. A total of 7,891 calf weight of cow at calf weaning (WCW) of 2,190 Nelore animals born between 1964 and 2015 were analyzed. The genetic analysis was performed under a multi-trait animal model considering WCW as a distinct trait for each year of age of the cow at calving. The model included the effects of contemporary group (herd and year of calf weaning, total of 105 levels), and the calf's month of birth. The age of the calf at weaning and cow's age at calving were considered as covariates (linear and quadratic). Animal and residual effects were considered as random. The heritability estimate of WCW was lower when the animal was younger (0.83), higher at maturity (0.94 at 8 years), decreasing with age (0.88). Genetic and phenotypic correlations were positive and mostly of high magnitude. It was observed a tendency of reduction in the correlation estimates between the WCW at more distant ages. With these results it can be affirmed that the WCW is a trait that is largely controlled by genetic component. Thus, the WCW can respond satisfactorily to the selection. The high genetic correlations observed for WCW indicate that selection for this trait at a given age should lead to the correlated response in the same sense at all other ages.