Energy and protein nutritional requirements for Nellore bulls

The objective of this study was to determine the nutritional requirements of energy and protein and estimate the efficiencies of metabolizable energy utilization for fat and protein deposition, as well as for maintenance (k(m)) and growth (k(g)). An experiment of comparative slaughter was carried out with thirty-seven 14-month-old (+/- 1 month) Nellore bulls with 259 +/- 24.9 k(g). Animals were divided as follows: five to reference, four to maintenance level and twenty-eight bulls feeding ad libitum. Bulls were also grouped in 4 different feedlot periods (42, 84, 126 and 168 days) for slaughter. The diet was composed of corn silage and concentrate, at a 55: 45 ratio. After the slaughter, the left half carcasses were totally dissected for determination of body composition. The energy requirements for maintenance were obtained by exponentially relating the heat production and the metabolizable energy intake, while the energy requirements for gain (NEg) were obtained according to empty body weight (EBW) and EBW gain (EBG). The net protein requirements for gain (NPg) were estimated according to EBG and retained energy (RE). The net (NEm) and metabolizable (MEm) energy requirements for maintenance were 76.5 and 113.84 kcal/EBW0.75/day, respectively. The k(m) was 0.67. The equations for NEg and NPg were: NEg (Mcal/day) = 0.0555 x EBW0.75 x EBG(1.095) and NPg (g/day) = 263.37 x EBG - 23.21 x RE. The k(g) was 0.33. The efficiencies to deposition of energy as protein and fat were 0.18 and 0.71, respectively. The model obtained for the percentage of retained energy as protein (% REp) was % REp = 2.4221 x (RE/EBG)(-1.6472). The net and metabolizable energy requirements for maintenance of Nellore bulls were 76.5 and 113.84 kcal/EBW0.75/day. The energy and protein requirements for gain could be obtained by the respective equations: NEg (Mcal/day) = 0.0555 x EBW0.75 x EBG(1.095) and NPg (g/day) = 263.37 x EBG - 23.21 x RE.