The objective of this work was to estimate the efficiency of metabolizable energy utilization (ME) for weight gain, and the requirements of metabolizable energy and total digestible nutrients in F1 Simental x Nellore bulls fed diets containing different concentrate levels. Twenty-nine animals averaging 17 of age and initial live weight of 354 kg were used. Five animals were slaughtered in the beginning of the experiment, as a reference, and the remainders were full fed and allotted to a completely randomized design, according to the dietary concentrate level: 25, 37.5, 50, 62.5, and 75%. Animals were slaughtered when they reached 500 kg. The dietary net energy concentrations were calculated, and the utilization efficiencies of the metabolizable energy for weight gain were estimated by regression analysis, among the net energies for gain, on the dietary metabolizable energy (ME). The ME requirements for 1 kilogram of empty body weight gain increased as the animal body weights raised, and decreased for the same live weight as the dietary concentrate levels increased. The efficiencies of metabolizable energy utilization estimated for weight gain were: .27, .26, .36, .39, and .42. The concentrate level improved the efficiency of ME utilization for weight gain.
crossbred bulls; efficiency; metabolizable energy; level of concentrate; diets
