Energy and protein requirements of young Holstein calves in tropical condition.

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.