the body composition and net protein and energy requirements for weight gain of 5/8 hostein-zebu crossbred cattle raised in brachiaria decumbens spaft pasture were evaluated. in total, 16 bulls with 10 months of age and body weight (bw) of 180 ± 19.95 kg were used. the animals were kept with free access to pasture or with restricted grazing (from 6 to 10 h). four animals were slaughtered at the beginning of the experimental period to estimate the empty body weight (ebw) and the initial body composition of the remaining animals. the other animals were slaughtered at the end of the 84-day trial period. the logarithm equations of the protein and energy body content were adjusted according to the logarithm of the empty body weight ebw. from these equations, the net protein and energy requirements for weight gain were estimated. there was an increase in fat (from 37.17 to 59.08 g/kg ebw) and energy (from 1.68 to 1.94 mcal/kg ebw) concentrations, with increase in body weight from 150 to 250 kg. the protein and energy requirements for gaining 1 kg of ebw increased with the increase in body weight or empty body weight. the relationship between fat concentration in gain and protein requirements also increased, indicating that as the bw or ebw increase, more fat deposition in the gain is observed.