This work was toevaluate the effects of different forage levels in the diet on the efficiencyof metabolizable energy (ME) utilization for maintenance and weight gain, andthe requirements of ME, total digestible nutrients (TDN) and metabolizable protein(MP). Forty-four pure Holstein bulls calves, 60 days old with initial averagelive weight (LW) of 78 kg were used. Eight reference animals were slaughteredat the beginning of the feeding trial. The remaining 36 animals were allottedin the treatments in a complete randomized experimental design, in four groupsof 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 andfour with 300 + 10 kg LW. The net energy (NE) contents of rations and the efficiencyof utilization of ME for maintenance and weight gain were calculated. The efficienciesof ME for weight gain were estimated by regression analysis, between net energyfor weight gain in function of dietary ME. The daily requirements of ME, TDNand MP were estimated. ME requirements for 1 kg of empty body weight (EBW) gainincreased with the EBW of the animals. The efficiency of EM utilization forweight gain were estimated as: .45, .40, .40 and .39, respectively for EM concentrationsof 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 TDNfor animals with 100, 200 and 300 kg LW were 10.06, 14.45, and 18.12 Mcal/dayand of 2.79, 4.00 and 5.02 kg/day, respectively. The efficiency of ME utilizationfor weight gain was greater for diets with low levels of forage.
