Our objective was to estimate the energy and protein requirements of Holstein young calves up to 87 days old. Forty-two Holstein calves aged 4 days were used. From these, ten were randomly selected and slaughtered to compose the baseline slaughter (BS) group. The remaining calves were randomly assigned to eight treatments in a 4 × 2 factorial using a completely randomized design. The treatments were 2, 4, 6, and 8 kg/day of milk (297 g/kg CP; 319 g/kg of fat) fed twice daily, and then harvested at 59 or 87 days of age. Calves were fed a starter (193 g/kg CP; 133 g/kg NDF) ad libitum in all treatments. The calves slaughtered at 87 days of age had milk replaced by Coast-cross (Cynodoon sp.) hay (125 g/kg CP; 728 g/kg NDF). The net requirement of energy for maintenance (NEm) was 0.36 MJ/kg EBWG, with efficiency of utilization of energy for maintenance (k m) of 59.4 %. The equation obtained to estimate the net requirement of energy for gain (NEg; MJ/d) was 4.40 × EBW(0.099), with the efficiency of utilization of energy for gain (k g) equal to 46.5 %. The observed requirements of net and metabolizable protein for maintenance (NPm and MPm) were 3.67 and 3.88 g/kg BW(0.75), respectively. The efficiency of use of metabolizable protein for maintenance (k pm ) was 94.6 %. The predicted requirements were higher than those observed in the literature, and this study demonstrated that the requirements of newborn calves are higher than the recommended.
Keywords: Comparative slaughter; Efficiency of utilization; Growth; Maintenance; Metabolizable energy; Metabolizable protein.