Figure 3.

Predicted effect of graded concentrations of phytate P (x) and log doses of phytase (v) on glycine digestibility in 21-day-old broilers. (a) Apparent ileal glycine digestibility (AID) was predicted with the equation: y = 315 − 1613x + 2426x² − 171v + 30.7v² + 1176xv − 1842x²v − 211xv² + 336x²v², adjusted R² = 0.88, RMSE = 1.46, P < 0.0001. In the absence of phytase, the AID of glycine was predicted to decrease in a non-linear manner from 75.3, 68.1, or 66.8% in birds fed diet containing 0.24, 0.345, or 0.45% phytate P, respectively. However, the inclusion of phytase at > 2,000 FTU/kg (log dose 3.301) was predicted to increase the AID of glycine in a non-linear-log manner, regardless of the phytate P content of the diet, and the maximum could not be predicted. (b) Apparent digestible glycine intake (g/D) was predicted with the question: y = 2.35 − 12.8x + 17.9x² − 1.17v + 0.17v² + 7.8xv − 11.2x²v − 1.17xv² + 1.67x²v², adjusted R² = 0.84, RMSE = 0.01, P < 0.0001. In the absence of phytase, the digestible intake of glycine was predicted to decrease in a non-linear manner from 0.38, 0.31, or 0.32 g/D in birds fed diets containing 0.24, 0.345, or 0.45% phytate P, respectively. The inclusion of phytase was predicted to increase the digestible intake of glycine in a non-linear-log manner, with 618 (log dose 2.791), 1,416 (log dose 3.151), or 724 FTU/kg (log dose 2.86) of phytase predicted to maximize the digestible intake of glycine in birds fed diets containing 0.24, 0.345, or 0.45% phytate P, respectively.