This work was to evaluate the effects of different forage levels in the diet on the efficiency of metabolizable energy (ME) utilization for maintenance and weight gain, and the requirements of ME, total digestible nutrients (TDN) and metabolizable protein (MP). Forty-four pure Holstein bulls calves, 60 days old with initial average live weight (LW) of 78 kg were used. Eight reference animals were slaughtered at the beginning of the feeding trial. The remaining 36 animals were allotted in the treatments in a complete randomized experimental design, in four groups of nine animals, in function of forage levels in the diet: 10, 25, 40 and 55%, on the DM basis, using chopped coast-cross (Cynodon dactylon) grass, ground corn and soybean meal, which constitute diets with approximately 16% CP. Five animals from each treatment were slaughtered with 190 + 10 kg LW and four with 300 + 10 kg LW. The net energy (NE) contents of rations and the efficiency of utilization of ME for maintenance and weight gain were calculated. The efficiencies of ME for weight gain were estimated by regression analysis, between net energy for weight gain in function of dietary ME. The daily requirements of ME, TDN and MP were estimated. ME requirements for 1 kg of empty body weight (EBW) gain increased with the EBW of the animals. The efficiency of EM utilization for weight gain were estimated as: .45, .40, .40 and .39, respectively for EM concentrations of 2.98, 2.76, 2.64, and 2.53 Mcal/kg of DM, obtained for the diets with 10, 25, 40, and 55 % of forage in the diets. The mean requirements of ME and TDN for animals with 100, 200 and 300 kg LW were 10.06, 14.45, and 18.12 Mcal/day and of 2.79, 4.00 and 5.02 kg/day, respectively. The efficiency of ME utilization for weight gain was greater for diets with low levels of forage.
Holstein calf; efficiency; metabolizable energy; forage level; protein