Abstract
The effect of feeding two levels of dietary crude protein (21 vs. 23%) in combination with or without two levels of GT 1.5 and 3 g/kg diet or one level of OTC at 0.1 g/kg was investigated on performance, carcass characteristics, organs weights, immunological response and meat quality traits in a factorial (2 x 4) experimental design. Each treatment was replicated four times with six chicks each. Birds were housed in a room with controlled environment and the experiment lasted from 1 to 45 days of age.
Decreasing dietary crude protein level to 21% had no adverse effect on growth rate, meanwhile, GT supplementation at 1.5 g/kg diet increased growth rate at 45 d of age and improved FCR by 10.4%. Dressing percentage of group fed diets containing 21% CF was increased compared to those of 23% one. Feeding 23% CP level significantly increased WBC's at 45 d of age and antibody response to TB at 21 d of age, while OTC supplementation to 23% CF level significantly increased WBC's compared to those supplemented with GT at both protein levels. Dietary CP did not significantly affect plasma total lipid and cholesterol, while increasing CP level significantly increased plasma triglyceride at both 21 and 45 d of age. Supplementation of low CF diet with 1.5 and 3.0 g GT or 0.1 g OTC/kg diet improved the sensory criteria of breast meat, whereas, feeding low CP diet supplemented with 3.0 g GT/kg diet improved the panel test criteria for thigh meat. In conclusion, broiler chickens may be fed 21% CP diet containing adequate methionine and lysine levels based on NRC (1994) when supplemented with 1.5 GT/kg diet from 1-45 d of age without negative effect on productive performance and meat quality. This may contribute to decreased environmental pollution by decreased nitrogen excretion and to more consumer safety in regard to AGP.