The effects of five dietary concentrate levels on the body composition and on the net requirements of protein and energy for weight gain were evaluated. Twenty nine F1 Simental Nellore bulls, averaging 17 months of age and initial 354 kg LW, were used. Five animals were slaughtered at the beginning of the experiment, as a reference, to estimate the initial empty body weight (EBW) and the initial concentrations of fat, protein and energy. The remaining animals were allotted to a completely randomized design, according to the dietary concentrate level: 25, 37.5, 50, 62.5 and 75%. Animals were full fed until a pre-established slaughter weight of 500 kg. The logarithm of amount of fat, protein or energy were regressed on the logarithm of the EBW, for each concentrate levels and for all levels of concentrate. By deriving those regression equations, the composition of the EBW gain was obtained. The amount of fat and the energy content in the weight gain increased as the animal LW increased. The body content of protein increased with the LW increasing, but the concentration in g/kg of EBW decreased. The net energy requirements for an animal with 400 kg EBW to gain 1 kg EBW were in an average 3.96 Mcal/day. The net energy requirements for weight gain increased whereas those of protein reduced with the increase of the body weight.
crossbred bovines; nutritional requirements; concentrate diet
