Body composition and energy and protein requirements for weight gain of bulls from four Zebu breeds

The body composition and the requirements for weight gain of energy and protein of cattle from four Zebu breeds (Gyr, Guzera, Mocho-Tabapua and Nellore) were estimated with 63 bulls averaging 24 months of age and 366 kg LW initial. Fifteen animals, four from Gyr, Guzera and Mocho Tabapua breed and three from Nellore breed, were slaughtered at the beginning of the trial and the remaining were allotted to three groups, with three animals from each breed, which were individually full fed a diet containing 50% concentrate(%DM), to reach target live weights of 405, 450 and 500 kg, respectively. Regression of the log of body content in energy, fat, and protein on log of the empty body weight (EBW) was fitted to estimate the total body content of those constituents for any EBW inside the range included in the research (250 to 450 kg). By differentiation of those regressions, the composition of EBW weight gain was rejusted. The animals from the four breeds did not differ regarding to body composition of fat, protein and energy. The requirements of protein and net energy for the rejusted weight gains were similar to the adopted by NRC (1996) and the metabolizable energy as the adopted by AFRC (1993).