Effects of Reduced Dietary Crude Protein and Amino Acids on the Performance, Carcass Characteristics and Intestinal Morphology of Broiler Chickens

A factorial experiment with a completely randomized design was carried out to examine the effects of reducing dietary crude protein (CP) and incorporating threonine, arginine, valine, isoleucine, and tryptophan synthetic amino acids supplements (SAA) on broiler chickens. The experiment involved 180 Ross 308 broilers divided into six treatments with six replicates each. The experimental treatments were as follows: 1- Standard diet, 2- Standard diet + SAA, 3- Diet with 2% reduced CP, 4- Diet with 2% reduced CP + SAA, 5- Diet with 4% reduced CP, and 6- Diet with 4% reduced CP + SAA. The 4% CP reduction diet decreased body weight gain in the starter and finisher periods (P < 0.05). The 4% lower CP also decreased feed intake in the grower, finisher and whole of the experiment (P < 0.05), and the same effect was observed for the 2% reduced CP diet only in the grower and entire experiment (P < 0.05). The same negative effects of lower dietary CP were also found for feed conversion ratio (FCR) (P < 0.05). The SAA supplements improved weight gain in the starter and the whole experimental period (P < 0.05). Feed intake did not show any change following SAA incorporation; however, SAA had a significant positive effect on FCR (P < 0.05). The only significant effect of experimental factors on small intestine morphology was a higher villus thickness in birds fed 2% less CP compared to the control (P < 0.05). The lower dietary CP led to increased serum cholesterol, triglyceride and HDL-c concentrations (P < 0.05). The serum total protein and albumen in the group fed 2% less CP was higher than the two other groups (P < 0.05). The only effect of SAA was an increased serum HDL level (P < 0.05). The results suggest that SAA supplementation could compensate for the negative effects of 2% but not the 4% lower dietary CP.