Evaluation of the responses of broiler chickens to varying concentrations of phytate phosphorus and phytase. Ⅰ. Starter phase (day 1–11 post hatching)

Growth performance, tibia ash, apparent ileal digestibility (AID), and total tract retention (TTR) of nutrients responses of broiler chickens fed diets containing varying concentrations of phytate P (PP) and a novel consensus bacterial 6-phytase variant (PhyG) from d 1 to 11 post hatching were evaluated with 1,152 broiler chicks. Diets were a nutrient-adequate positive control diet (PC) with 2.8 g PP/kg or one of 15 nutrient-reduced negative control (NC: PC minus 88 kcal/kg ME, 0.8 g/kg dig. Lys, 2.0 g/kg available P, 1.8 g/kg Ca and 0.5 g/kg Na) diets with 3 PP (g/kg) levels, mainly from rice bran, at 2.3 (NC1), 2.8 (NC2), or 3.3 (NC3) and 5 PhyG supplementation at 0, 500, 1,000, 2,000, or 4,000 FTU/kg in a 1 + 3 × 5 factorial. All treatments had 6 replicate cages with 12 birds per cage. Despite comparable PP levels, birds fed the PC diet had greater (P ≤ 0.01) body weight (BW), feed intake (FI), tibia ash, AID of energy, AA, P, and Ca as compared with birds fed the NC2 without phytase. There was no interaction between PP and phytase for all responses. Increasing PP concentrations linearly decreased (P < 0.01) BW, FI, AID, and TTR of P and Ca. With phytase supplementation, there was a quadratic response (P < 0.05) in BW, FI, tibia ash, and a linear increase (P < 0.05) in the AID of energy, nitrogen, and all the measured AA. Increasing phytase dose from 0 to 4,000 FTU/kg increased (P < 0.01) AID of P and Ca by 88 and 18%, respectively. There was also a quadratic response (P ≤ 0.05) on TTR of P and Ca with increasing phytase dose. In conclusion, increasing levels of PP reduced growth performance and most nutrient utilization responses of broiler chickens while phytase supplementation positively impacted the responses of broiler chickens during d 1 to 11 post hatching.