Effect of low protein diet supplemented with crystalline amino acids on broiler chickens was allocated. 96 female commercial broiler chicks were chosen at 10 days of age based on body weight and used for 21 days of this experiment. This study was conducted in completely randomized design with 20, 18, and 16% crude protein supplemented with crystalline amino acids. Treatments received the same basal diets(corn-soybean meal). The experimental units were allocated to 3 dietary treatments with 4 replicates and 8 chicks per replicate. Birds fed diets in which crude protein was in a stepwise manner from 20 to 16% . Ileal digestible quantities of all essential amino acids were almost equal in the diets and maintained at above NRC (1994) recommendations. Body weight gain, feed intake, feed conversion ratio were measured at the end experiment. At 31 days of age 8 birds from each treatment with a body weight close to the replicate mean were randomly taken for carcass weight, and abdominal fat, liver, gizzard, as percents of carcass weight. Significant effect (P<0.05), was observed among percentages of crude protein diets. Fortifying a low crude protein diet with essential amino acid resulted in more increase in body weight gain, feed intak and favorable decrease in feed conversion ratio. The relative weight of abdominal fat increased significantly(P <0.05) in low crude protein diets. The amount of excreted nitrogen was reduced(P<0.05), with decrease crude protein levels. This research indicated that dietary crude protein can be decrease until 16% (supplemented with crystalline amino acids).
