Effect of dietary protein level on performance of early-weaned double-muscled calves1

The effect of the protein content of the concentrate on the performance during a 20-week rearing period was investigated, using thirty-two male and thirty-seven female newborn double-muscled calves, belonging to the Belgian White–Blue breed. A restricted milk diet was fed. Weaning occurred when daily concentrate consumption reached 0.5 kg. The crude protein content of the concentrate amounted to 15% (LP) or 18% (HP) on an as-fed basis. Concentrate and grasshay were fed from a 2-week age onward. Daily concentrate intake was limited to a maximum of 3 kg, while hay was freely available. Weaning occurred at a similar live weight (LP: 80.1 vs. HP: 80.7 kg) and after a similar number of experimental days (LP: 60.5 vs. HP: 57.4 days). Total dry matter (DM) intake during the entire period (LP: 260.2 vs. HP: 267.2 kg) was not affected by dietary crude protein. Liveweight gain after weaning (LP: 0.98 vs. HP: 1.05 kg/d) and during the entire rearing period (LP: 0.78 vs. HP: 0.84 kg/d) was increased when the HP concentrate was fed. DM and net energy were more efficiently used in calves fed the HP concentrate, while protein was less efficiently converted at the higher dietary protein level. Higher dietary protein also increased serum urea concentration. Based on an increased liveweight gain and a better conversion of DM and net energy, on the one hand, and a reduced protein efficiency and a higher serum urea concentration on the other hand, it is concluded that a dietary level of 200 g crude protein (CP) or 114 g true protein digested in the small intestine (DVE) per kg DM is near the optimum in early-weaned double-muscled calves. It improved daily liveweight gain and feed conversion, compared to 167 g CP or 100 g DVE per kg DM. These results give evidence that the optimal dietary protein level in early-weaned double-muscled calves seems to be higher than in non-double-muscled calves.