Journal of animal physiology and animal nutrition-zeitschrift fur tierphysiologie tierernahrung und futtermittelkunde vol:73 issue:4 pages:213-223
Over 2 consecutive years, 24 and 51 Belgian white-blue double-muscled bulls, respectively, were used to study the influence of three protein levels, during a liveweight interval from 375 to 720 kg, on performance and carcass and meat quality. The diets contained 77 (L), 85 (M) and 97 (H)g DPI (digestible protein in the intestine) per kg dry matter, respectively, and 137, 146, and 166 g crude protein. Initially, the dairy liveweight gain of the lowest protein group was slightly lower: 1.41 kg vs. 1.48 kg for M and H. Afterwards, the animals of group L achieved a partial compensatory gain, so that the average daily gain for the entire experimental period hardly differed (p > 0.05) among groups (L: 1.30 kg; M and H: 1.34 kg). Daily dry matter and net energy intake per kg metabolic weight were not influenced by the increasing protein intake, while feed efficiency was only slightly improved. No differences in carcass-quality parameters were observed. A protein level of 77 g DPI or 137 g crude protein in the dry matter of the complete diet may suffice to attain optimum beef production with white-blue double-muscled bulls during a finishing period from 375 to 720 kg. Higher protein levels decreased serum thriiodothyronine and increased thyroxine. Mean N-retention at 400 and 600 kg was 32 % higher for the H ration (54.3 g/day) compared with the L ration (41 g/day), but the effect was not significant due to a large variation. The H ration also increased N-excretion.