Abstract
This study was performed to evaluate the effect of supplementation of low crude protein (CP) corn-soybean meal diets which contained low ME levels with lysine (Lys), methionine (Met) and threonine (Thr) above that recommended by the National Research Council (NRC, 1994) on broiler performance, carcass characteristics and serum constituents from 12 to 33 d of age. A total of 100 Ross chicks were randomly distributed in a randomized complete block design among 20 cages with 5 replicate cages / treatment with four dietary treatments: T1=Control diet (21% CF and 3150 kcal/kg ME); 12, T3 and 14 contained 19.5% CF and 115% of Lys, Met and 108% of Thr compared to the NRC requirements; 12, 13 and 14 contained 3150, 3100 and 3050 kcal of metabolizable energy (ME)/kg, respectively. Cumulative feed intake, body weight gain and feed conversion ratio from 12 to 33 d of age was not affected by treatment. Birds which had received T2 and T3 had a higher dressing percentage compared to those which had received T1. Breast muscle yield followed the same trend; heavier breasts were obtained from birds which had received T2 and T3. Serum uric acid concentration was influenced by treatment; it was significantly higher for birds which had received the control diet compared to all other treatments. Based on presented evidences, it can be concluded, that by fortifying crystalline amino acids to broilers diet at this stage of production, dietary CP and ME could be reduced to 19.5% and 3050 kcal/kg; respectively.