Figure 3.

Predicted effect of graded concentrations of phytate P (x) and log doses of phytase (v) on broiler tibia parameters at day 21. A. Tibia ash weight in grams was predicted with the equation: y = 1.063 − 1.572x + 1.204v − 0.206v², adjusted R²=0.53, RMSE=0.17, P < 0.0001. Maximum tibia ash weight was achieved at 822 phytase units (FTU)/kg of phytase, regardless of dietary phytate P concentration or ≤0.24% phytate P, regardless of phytase concentration in the diet. B. Tibia ash concentration (%) was predicted with the equation: y = 33.32 + 78.79x − 133.3x² + 1.512v, adjusted R²=0.47, RMSE=1.69, P < 0.0001. Maximum tibia ash concentration was achieved at 2,000 FTU/kg of phytase, regardless of the dietary phytate P concentration or ≤0.296% phytate P, regardless of phytase concentration in the diet. C. Tibia calcium concentration (%) was predicted with the equation: y = 33.22 + 13.31x − 33.42x², adjusted R²=0.54, RMSE=0.79, P < 0.0001. Maximum tibia calcium concentration was achieved at ≤0.24% phytate P, regardless of phytase dose in the diet. Tibia phosphorus concentration and bone breaking strength were not determined due to the poor fit of the model.