Six Nellore bulls, with initial body weight of 420 kg, were assigned to a duplicated 3x3 Latin square design to evaluate the effects of replacing a true protein source (soybean meal), of high biological value, in a rumen degradable protein (RDP) deficient diet, by urea or starea (a supposedly slow release nonprotein nitrogen source), both in a RDP adjusted diet. In natura sugarcane bagasse as the only source of forage (20% of DM). Evaluated parameters were: rumen ammonia-N concentration, plasma urea-N, glucose and nitrogen balance. Experimental treatments were: 1) soybean meal (SBM); 2) urea and 3) starea (A-150S). Diets were isonitrogen (13% CP). The rumen ammonia-N concentration was higher in the treatment with urea, compared to the treatment with SBM, and starea showed no difference compared to the others. Starea had higher loss of urinary N. N retention (g/d and % of consumed) and protein biological value (N retention, % of N digestible) were higher for urea treatment, compared to the others. There was no difference on plasma urea-N and glucose concentration among treatments. Total replacement of SBM by urea, adjusting PDR in diets for growing beef cattle, demonstrated to be viable. Conventional urea showed advantage compared to starea.
starea; blood parameters; nitrogen balance; ruminal ammonia-N; beef cattle
