FIXED EFFECTS IN THE FORMATION OF A COMPOSITE LINE OF BEEF-CATTLE .2.PREWEANING AND POSTWEANING GROWTH AND CARCASS COMPOSITION

Generation, age of dam, sex of calf, and certain covariates were studi ed to elucidate their effect on traits related to growth and carcass c haracters measured on individuals from a stabilized three-breed compos ite (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 diffe rent from zero (P > .05) for birth weight, weaning weight, and prewean ing ADG. There were few important differences between generations for carcass traits as well. This may have been caused by confounding of in dividual and maternal heterotic effects with direct and maternal compo nents of the model, or the partial confounding of years, age of dam, a nd generation. Birth weight was curvilinear with respect to calving da y (P < .01). Age of dam was important for all growth traits except pos tweaning ADG. In general, growth of calves increased with increasing a ge of dam, as did carcass weight and predicted retail product. Individ ual breed additive effects (differences between calves sired by C and T sires mated to RA dams) were positive for birth weight (P < .01), we aning weight (P < .05), carcass weight (P < .05), and predicted retail product (P < .05). Maternal breed additive effects (differences betwe en 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). Individual heterosis was large and positive for birth weight (P < .01) , final weight (P < .01), and postweaning ADG (P < .01) and all carcas s traits except fat depth. Maternal heterosis was noted for birth weig ht (P < .05); final weight (P < .05); postweaning ADG (P < .05); kidne y, pelvic, and heart fat (P < .01); and marbling score (P < .01).