This work was carried out to estimate the efficiency of metabolizable energy utilization (EMEU) for maintenance (km) and weight gain (kf) and the requirements of metabolizable energy (ME) and total digestible nutrients (TDN) of Nellore bulls. Thirty-five animals, averaging 330 kg and 20 months old, were used. After the period of adaptation (40 days), five animals were slaughtered as reference. The remaining animals were allotted, in a completely randomized design, to the treatments (12.5, 25.0, 37.5, 50.0, 62.5, and 75.0% of concentrate), in dry matter basis. The kf estimate was effected from the regression among net energy contents for gain, in function of dietary ME, and also grouping data relative to the animals of the present work and the ones of the 29 F1 Simental x Nellore bulls. The kf were also estimated as the coefficient of the linear regression between the retained energy (RE) and the ME intake (MEI). The estimated km was .56. The estimated kf using the first methodology were .45, .35, .54, .50, and .54, respectively, for the concentrations of 2.11, 2.35, 2.51, 2.59, and 2.52 Mcal/kg DM. The kf estimated by means of the second methodology were .32, .33, .44, .49, and .69, respectively. The ME and TDN requirements to maintain a 400 kg LW animal were 11.94 Mcal/kg EBWG and 3.30 kg/kg EBWG, respectively, while for weight gain, the requirements for the diets with 2.4 Mcal/kg DM, were 9.84 Mcal/kg EBWG and 2.72 kg/EBWG. For the diets with ME concentration of 2.6 Mcal/kg DM, the ME and TDN requirements were7.28 Mcal/kg EBWG and 2.01 kg/EBWG, respectively.
concentrate; efficiency; metabolizable energy, total digestible nutrients
