Energy and protein requirements for Angus and Nellore young bulls

Thirty-two animals with initial body weight (BW) of 380±5.2 kg were used to determine energy and protein requirements of Nellore and Angus young bulls using the comparative slaughter technique. Four animals per breed were slaughtered at beginning of the experiment. The remainder were housed in individual stalls, where eight animals per breed were fed ad libitum a silage/concentrate (SC) diet (300 g/kg of silage and 700 g/kg of a concentrate based on corn and soybean meal, DM basis). Another 4 animals per breed were fed the SC diet at 55% of their dry matter intake adjusted for the metabolic BW of animals that received the SC diet ad libitum. Intake was measured daily and a metabolism trial was conducted with total collection of feces and urine. The data were used then to estimate the metabolizable energy intake. After 84 d of growth the cattle were slaughtered.The data were analyzed using the GLM and NLIN procedures of SAS adopting significance level of 0.05. The metabolizable energy requirements for maintenance differed between Angus and Nellore: 0.580 versus 0.456 MJ/kg BW0.75·d−1 when calculated by logarithm model and 0.559 versus 0.483 MJ/kg BW0.75·d−1 when calculated by nonlinear model. There was no difference between breeds in the nutritional requirements for growth. Our results support that Zebu bulls have lower net energy requirements for maintenance than Bos taurus taurus bulls.