Evaluation of growth curves of Brahman cattle of various frame sizes.

Partial stage and complete life-cycle growth curves of Brahman cattle were obtained for small, medium, and large frame sizes for a herd under grazing conditions in a subtropical environment. Data were grouped into three stages : birth to weaning (stage 1), weaning to 20 mo (males) or 32 mo (females) of age (stage 2), and 32 mo of age to maturity (females only ; stage 3). Within each stage, multiplicative growth models were developed for each frame size and sex. Body weight growth on age t was represented as exp(a + bt + ct 2 ) for stages 1 and 2, and as exp(A + B exp(kt)) for stage 3. The effects of sire and progeny within sire were considered in all models. For stages 2 and 3, the effect of season was also included. To obtain complete life-cycle curves, a growth stage-multiplicative model with stages 1 and 2 was defined ; stage 3 was also included for females. Due to a 1-mo adaptation period after weaning, a transition stage between stages 1 and 2 was defined and represented by the model exp(a + bt). In stage 1, the shape of the growth curve differed (P <.05) among frame size groups ; sex did not affect the shape of the growth curves, but bull calves had heavier ( P < .05) weights than heifer calves. In stage 2, the shape of the growth curves did not differ among frame sizes, but BW differed among frame sizes ( P <.05) and sex affected ( P <.05) the shape of the growth curves. In stage 3, the shape of the growth curves differed ( P < .05) among frame sizes. There were sire effects (P < .05) for stages 1 and 2, but sire effects were not significant for stage 3. Season effects were important (P <.05) for stages 1 and 2. These results suggest that variability in growth patterns provides an opportunity to use management and nutrition to improve production efficiency in cattle of different frame sizes.