Growth performance, nutrient utilisation and carcass composition respond to dietary protein concentrations in broiler chickens but responses are modified by dietary lipid levels

A total of ten experimental diets with protein concentrations ranging from 154 to 400 g/kg and two lipid levels (46 and 85 g/kg) with identical energy densities were offered to 240 male Ross 308 broilers from 7 to 28 d post-hatch. Growth performance was monitored and nutrient utilisation (apparent metabolisable energy (AME), N-corrected AME (AMEn), AME daily intake, AME:gross energy ratios, N retention) was determined. The weight gain response of broiler chickens to dietary protein concentrations in diets containing high and low lipid levels was diverse, with the relevant quadratic regressions being significantly different (PP>0·05). AMEn was also linearly (PPr 0·933, PR2=0·93, P