Fixed effects in the formation of a composite line of beef cattle: II. Pre- and postweaning growth and carcass composition.

Generation, age of dam, sex of calf, and certain covariates were studied to elucidate their effect on traits related to growth and carcass characters measured on individuals from a stabilized three-breed composite (1/2 Red Angus [RA], 1/4 Charolais [C], 1/4 Tarentaise [T]). There was evidence that sires had been selected for yearling weight. Thus, an animal model was fitted to the data to estimate the effects free of bias due to selection. Differences between generations were not different from zero (P > .05) for birth weight, weaning weight, and preweaning ADG. There were few important differences between generations for carcass traits as well. This may have been caused by confounding of individual and maternal heterotic effects with direct and maternal components of the model, or the partial confounding of years, age of dam, and generation. Birth weight was curvilinear with respect to calving day (P < .01). Age of dam was important for all growth traits except postweaning ADG. In general, growth of calves increased with increasing age of dam, as did carcass weight and predicted retail product. Individual breed additive effects (differences between calves sired by C and T sires mated to RA dams) were positive for birth weight (P < .01), weaning weight (P < .05), carcass weight (P < .05), and predicted retail product (P < .05). Maternal breed additive effects (differences between calves out of C x RA or T x RA dams) were also positive for weaning weight (P < .05), carcass weight (P < .05), and fat depth (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)