Growth Performance, Bone Mineralization, and Nutrient Retention Responses of Chicks to Dietary Crude Protein and Non-phytate Phosphorus Concentrations

Abstract

The objective of this study was to investigate possible interactions between dietary crude protein (CP) and phosphorus (P) in broiler chicks. Two CP levels including an adequate NRC-recommended 230 g/kg or an amino acid-supplemented reduced CP 180 g/kg and 4 level - 4.0, 4.5, 5.0, or 5.5 g of non-phytate P (NPP)/kg in a 2 X 4 factorial arrangement were fed to 6 replicate cages of 6 chicks per cage from 10 to 22 d of age. There were main effects of CP (P < 0.001) and NPP (P < 0.05) concentration on final body weight (FBW), body weight gain (BWG), and gain-to-feed ratio. There was a linear reduction (P < 0.05) in feed intake as dietary NPP level increased. Generally, FBW, BWG and FI were linearly reduced (P < 0.05) with increasing NPP. Gain-to-feed ratio was lower (P < 0.05) for chicks fed the AA-supplemented reduced CP diet than those fed the adequate protein diet. Tibia ash was increased linearly (P < 0.05) with increased dietary NPP, but was not affected by CP. There were both linear and quadratic effects (P < 0.05) of NPP on retention of dry matter and energy. At either CP level, retention of nitrogen and phosphorus was reduced (P < 0.05) with increase in dietary NPP. Retention of P was linearly reduced with increasing NPP concentration and highest in chicks fed the adequate CP diet. These results provide support for an integrated strategy for reducing manure N and P excretion by broiler chickens.