A trial was carried out to evaluate the effect of low crude protein (CP) diets, supplemented with amino acids, on the starting barrows performance. Forty barrows genetically improved, of commercial dam line, were allotted to an experimental randomized complete block design, with four treatments, five blocks and two animals per experimental unit. The four treatments were: 18.73% P .96% L - corn-soybean meal diet containing 18.73% of CP and 0.96% of digestible lysine; 16.86%P + L - it was constituted of a diet with 10% lower CP than previous and the lysine level was corrected; 16.86%P +L+M+T - it was formulated a diet with 10% lower CP than first treatment. The lysine, methionine + cystine and threonine level were corrected, with synthetic amino acids, to reach the ideal protein pattern; 17.79%P+L+M+T - it was similar to previous, however with 5% lower CP than that one obtained in the first treatment. There was no effect on performance, in the periods 0-14, 14-21 and 0-21 days of evaluation. The CP reduction was effective to decrease the plasma urea nitrogen (PUN). The cost in diet, per kilogram of gained live weight, was the same for all the treatments. The results indicated that diets with low crude protein, with synthetic amino acids supplementation, based on the ideal protein concept, do not impair the performance and economic variables, and furthermore provided the reduction in the nitrogen excretion.
synthetic amino acids; slurry; low protein; blood components; environmental pollution
