Six Nellore bulls,with initial body weight of 420 kg, were assigned to a duplicated 3x3 Latinsquare design to evaluate the effects of replacing a true protein source (soybeanmeal), of high biological value, in a rumen degradable protein (RDP) deficientdiet, by urea or starea (a supposedly slow release nonprotein nitrogen source),both in a RDP adjusted diet. In natura sugarcane bagasse as the onlysource 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 comparedto the others. Starea had higher loss of urinary N. N retention (g/d and % ofconsumed) and protein biological value (N retention, % of N digestible) werehigher for urea treatment, compared to the others. There was no difference onplasma urea-N and glucose concentration among treatments. Total replacementof SBM by urea, adjusting PDR in diets for growing beef cattle, demonstratedto be viable. Conventional urea showed advantage compared to starea.
