COMPONENTS OF (CO) VARIANCE OF THE WEANING WEIGHT IN THE CUBAN ZEBU BERMEJO BEEF CATTLE

Abstract

SUMMARY With the objective of estimating the components of (co)variance of weaning weight in Cuban Zebu Bermejo cattle, a sample of 5120 records was taken of female and male animals that were born between 1988 and 2007 in three flocks located in the provinces of Cienfuegos, Camagüey and Granma. Six different statistical models were used, which had in common as fixed effects the group of contemporaries (year-herd-period-sex) and the co-variables; linear weaning age, age of the mother at linear and quadratic birth. The random effect of the animal was common to all of the models, the maternal, genetic, additive and environmental effects were alternated according to the case, along with the additive genetic co-variance among the direct and maternal effects. Weaning weight reached a mean of 159.7 kg, with a standard deviation of 26.7 kg. Three criteria were used (log L, AIC and BIC) for comparing the models. Model 1 had the worst fit considering the three criteria. Taking into account criterion log L, models 5 and 6 do not differ significantly from each other and were the best with respect to the rest. Criteria AIC and BIC indicate model 5 to be the best. The heritability for the direct additive effect (0.320) in model 1 was much higher than that estimated for the rest of the models (0.023-0.061), which indicates that ignoring the maternal effects produced an overestimation of this parameter. The heritabilities estimated for maternal effects in the models with the best fit reached values of 0.059 (model 5) and 0.045 (model 6), which, although higher than those of the direct effect, were also low. The effects of the permanent environment determined between 10.9 % (model 6) and 15.4 % (model 3) of the total variability. The genetic correlation between the direct and maternal effects reached values of 0.534 and 0.614 for models 4 and 6, respectively, although it should be considered with caution. Results indicate that there is little possibility of improving weaning weight by selection in the present population.