Figure 1.

Predicted effect of graded concentrations of phytate P (x) and log doses of phytase (v) on broiler growth performance from hatch to day 21. A. Feed intake (FI) in grams was predicted with the equation: y = 754.7 + 921.8x − 1,670x² + 204.2v − 37.05v², adjusted R²=0.33, RMSE=37.5, P < 0.0001. Maximum FI was achieved at 561 phytase units (FTU)/kg of phytase, regardless of dietary phytate P concentration or ≤0.275% phytate P, regardless of phytase concentration in the diet. B. Body weight gain (BWG) in grams was predicted with the equation: y = 409 + 1,369x − 2,324x² + 172.7 − 27.72v², adjusted R²=0.55, RMSE=29.7, P < 0.0001. Maximum BWG was achieved at 1,285 FTU/kg of phytase, regardless of the dietary phytate P concentration or ≤0.294% phytate P, regardless of phytase concentration in the diet. C. Feed conversion ratio (FCR) was predicted with the equation: y = 1.593 − 1.117x + 1.772x² − 0.033v, adjusted R²=0.66, RMSE=0.02, P < 0.0001. Optimum (lowest) FCR was achieved at 2,000 FTU/kg of phytase, regardless of the phytate P concentration or ≤0.319% phytate P, regardless of the phytase concentration in the diet.