Dietary crude protein reductions in wheat-based diets with two energy densities compromised performance of broiler chickens from 15 to 36 days post-hatch
Shemil P. Macelline, Peter V. Chrystal, Mehdi Toghyani, Peter H. Selle, Sonia Yun Liu
Abstract
This study was designed to investigate the impacts of two energy densities (13.0 and 12.5 MJ/kg ME) in wheat-based diets with three tiers of CP concentrations (210, 190, 170 g/kg) on the performance of broiler chickens. The parameters assessed included growth performance, (15 to 36 days post-hatch), carcass traits, nutrient utilisation, starch-protein digestive dynamics, apparent ileal amino acid digestibility coefficients and the free amino acid and ammonia (NH3) 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% (1890 versus 2158 g/bird) and FCR by 5.33% (1.501 versus 1.425). The 0.5 MJ energy density reduction compromised FCR by 3.25% (1.525 versus 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 non-bound amino acid inclusions) linearly associated to increased plasma ammonia (NH3) concentrations (r = -0.607; P = 0.010) and plasma NH3 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 NH3 concentrations have profound implications for the successful development of reduced-CP, wheat-based broiler diets.