A trial involving nineteen zebu steers with initial live weight of 270 kg were conducted with the objective of determining their energy requirements and the efficiency of utilization of the metabolizable energy for gain (k g) and maintenance (k m). Four steers were slaughtered at the beginning of the trial, performing the reference group, three were fed at maintenance level and the remaining were uniformly allotted to a complete randomized design, in three treatments, with different levels of concentrate in the diets (5, 35 and 65%, in the total dry matter basis). Haylage of Brachiaria brizantha and Cynodon sp was used as roughage. The diets were isonitrogenous and the animals were fed ad libitum. The net energy requirement for maintenance (NEm) was estimated as the antilog of the intercept of the equation obtained by the linear regression between the logarithm of heat production (HP) and the metabolizable energy intake (MEI). It was also determined as the "a" coefficient of the exponential equation obtained between HP and MEI of the animals from the treatment with 35% of concentrate plus the animals from the maintenance group. The amount of energy and fat in the gain increased as the body weight of the animals increased. The identity test of models showed no differences among the treatments. The daily energy requirement for maintenance was 68.60 kcal/LW0.75. The estimated value for k m was 0.66 and the calculated k g were 0.26, 0.41 and 0.46, respectively, for contents of metabolizable energy of 2.31, 2.47 and 2.62 Mcal/kg DM, corresponding to the levels of 5, 35 and 65% concentrate in the diet. The daily requirements of metabolizable energy (ME) and total digestible nutrients (TDN) for maintenance of a steer with 400 kg of live weight were, respectively, 9,30 kcal and 2.57 kg.
bovine requirements; digestible energy; metabolizable energy; net energy; utilization efficiency; zebu cattle
