Dietary crude protein reductions in wheat-based diets with two energy densities compromised performance of broiler chickens from 15 to 36 days post-hatch

This study was designed to investigate the impacts of 2 energy densities (13.0 and 12.5 MJ/kg ME) in wheat-based diets with 3 tiers of CP concentrations (210, 190, and 170 g/kg) on the performance of broiler chickens. The parameters assessed included growth performance (15–36 d posthatch), carcass traits, nutrient utilization, starch–protein digestive dynamics, apparent ileal amino acid digestibility coefficients, and the free amino acid and ammonia (NH(3)) concentrations in systemic plasma. Also, the feasibility of substituting soybean meal with canola meal in 190 g/kg CP diets was investigated. The dietary CP reduction from 210 to 170 g/kg significantly compromised weight gain by 12.4% (1,890 vs. 2158 g/bird) and FCR by 5.33% (1.501 vs. 1.425). The 0.5 MJ energy density reduction compromised FCR by 3.25% (1.525 vs. 1.477; P = 0.013) in birds offered 170 g/kg CP diets. Reducing dietary CP and energy densities interactively influenced (P = 0.027) apparent metabolizable energy (AME) and nitrogen corrected metabolizable energy (AMEn) (P = 0.022) such that reducing dietary CP increased these parameters but reducing dietary energy densities decreased AME and AMEn. The 150 g/kg canola meal inclusion with the elimination of soybean meal displayed some promise. Dietary CP reductions (and increased nonbound amino acid inclusions) linearly associated with increased plasma ammonia (NH(3)) concentrations (r = −0.607; P = 0.010) and plasma NH(3) was linearly related to depressed weight gains (r = −0.565; P = 0.018). The association of dietary non–protein-bound amino acid (NPBAA) inclusions and elevated plasma NH(3) concentrations have profound implications for the successful development of reduced-CP, wheat-based broiler diets.