Thirty-three 39 crossbreed Holstein-Gyr steers were used in a research aiming to evaluate the effects of feed restriction prior to the confinement on the changes in body composition and in the net requirements of energy for maintenance and weight gain, and protein for weight gain. Thirty animals were submitted to a high grazing pressure, while the remaining nine steers had unrestricted access to forage (continuous gain group), after what, six animals from the first group and three from the second group were slaughtered, and the remaining animals were confined. From 24 animals of the compensatory growth group, 12 were fed ad libitum (compensatory growth group) and 12 were fed 15% above the maintenance level (maintenance group), while six animals from continuous gain group were fed the same ad libitum diet. The diet was constituted by corn silage and 26% of concentrate. The net energy requirement for maintenance was determined by regression of the heat production, in function of the metabolizable energy intake (ME), adjusting for heat production at zero level. Regression equations of the log of the body contents of fat, protein and energy in function of the log of the empty-body weight (EBW) were fitted. The average maintenance net energy requirements for the animals in the compensatory growth group was 47,50 kcal/kg0.75/day. The total fat and energy content in body-weight-gain increased as body live weight increased. The net requirements of energy and protein for 1 kg of EBW gain were 3.13 Mcal/day and 189.4 g/day, respectively, for a 300 kg live weight steer.
bovine; body content; energy; nutritional requirements; protein
