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 unde r grazing conditions in a subtropical environment. Data were grouped i nto 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 (fe males 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 ex p(A + B exp(kt)) for stage 3. The effects of sire and progeny within s ire were considered in all models. For stages 2 and 3, the effect of s eason was also included. To obtain complete life-cycle curves, a growt h 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 w eaning, a transition stage between stages 1 and 2 was defined and repr esented 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 t he shape of the growth curves, but bull calves had heavier (P < .05) w eights 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 importa nt (P < .05) for stages 1 and 2. These results suggest that variabilit y in growth patterns provides an opportunity to use management and nut rition to improve production efficiency in cattle of different frame s izes.