Effects of a high level of phytase on broiler performance, bone ash, phosphorus utilization, and phytate dephosphorylation to inositol.

An experiment was conducted to evaluate how the addition of microbial phytase influenced growth performance, bone mineralization, tissue P content, apparent digestibility and retention, and inositol phosphate (IP) concentrations in broilers fed diets with varying mineral matrices from 2 to 23 d of age. At 2 d of age, chicks were randomly allotted to receive 1 of 6 experimental diets arranged as a 3 × 2 factorial of mineral matrix [control diet with 1.0% Ca and 0.5% non-phytate phosphorus (NPP); mineral matrix 1 with 0.84% Ca and 0.35% NPP; and mineral matrix 2 with 0.77% Ca and 0.29% NPP] and phytase supplementation (0 or 1,500 FTU/kg). Feed intake was influenced (quadratic, P = 0.012) by the mineral matrix, but no interaction or main effect of phytase were observed. Phytase increased (P = 0.011) BW gain regardless of the mineral matrix applied. Feed efficiency was not influenced (P > 0.05) by mineral matrix, phytase, or their interaction. Phytase increased bone ash content differentially across matrices (interaction, P < 0.01), and tibia P content was lowest in birds fed matrix 2 and highest in the control (linear, P < 0.05). Concentrations of P in muscle, spleen, and liver were not affected by treatment. An interactive effect (P < 0.01) was observed for apparent ileal digestibility (AID) of P, where phytase increased AID in matrix 1. An interactive effect (P < 0.01) was observed for apparent retention of P and Ca, where phytase reduced P and Ca retention in the control diet. A main effect (P < 0.01) of mineral matrix was observed for AID of Ca, with birds fed matrix 1 having the lowest AID of Ca compared with control and matrix 2 treatments. Phytase influenced (P < 0.05) IP concentrations differently across matrices. Overall, phytase and the mineral matrix, either as main effects or in an interactive manner, influenced growth performance, apparent nutrient digestibility and retention, bone and IP concentration responses in broiler chicks.