ABSTRACT
Experiment I: T1-1 = basal diet with 25% crude protein (CP) + limiting amino acids (LA); T1-2 = 20% CP + LA; T1-3 = 20% CP + LA + L-glycine; T1-4 = 20% CP + LA + L-glutamate; T1-5 = 20% CP + LA + L-glycine + L-glutamate. Experiment II: T2-1 = basal diet with 22% CP + LA; T2-2 = 20% CP + LA; T2-3 = 17.6% CP + LA + L-glycine; T2-4 = 17.6% CP + LA + L-glutamate; T2-5 = 17.6% CP + LA + L-glycine + L-glutamate. The reduction of dietary protein based on the concept of ideal protein decreases nitrogen excretion in quails when L-glycine is added to the diets. Quails fed diets supplemented with L-glutamate as the non-specific nitrogen source equivalent to the nitrogen level of the control diet had increased nitrogen excretion. However, quails had reduced nitrogen excretion in both experiments when L-glycine was added to diets with L-glutamate. Carcass fat was increased by reducing dietary protein, but fat deposition was reduced by adding L-glutamate and L-glycine, or both. The dietary addition of L-glutamate and L-glycine in quails based on the ideal protein concept is not necessary (Exp. I). Although the total nitrogen, electrolytic balance and glycine level were adjusted in diets, quails had decreased performance. Therefore, other hypotheses besides protein reduction need to be studied (Exp. II). Protein reduction with supplementation of only limiting essential amino acids does not affect quail performance. Dietary addition of L-glycine reduces nitrogen excretion.
