The objective of this work was to evaluate the effects of different forage levels in the diet on the body composition, net energy for maintenance and weight gain and net protein requirements for weight gain. Fifty-two 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. Another group of eight animals were fed diet with 90% of forage and 10% of concentrate to meet the requirements slightly above maintenance (maintenance group). 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) requirement for maintenance was estimated from the regression equations between the logarithms of produced heat and the metabolizable energy intake (MEI), assuming MEI equal to zero. Regression analysis, of the logarithm of the amounts of fat, protein and energy, in function of the logarithm of empty body weight (EBW) were fitted. The energy requirement for maintenance was in average 110.46 kcal/kg.75. The amount of fat and the energy content of weight gain increased as the animal LW increased, for all forage levels of the diet and in overall. The net energy and protein requirements for 1 kg of EBW gain were 2.83 Mcal/day and 183.20 g/day, respectively. The net energy and protein requirements for weight gain of Holstein calves increased with the increase of the empty body weight.
Holstein calf; body composition; energy; nutritional requirements; protein