Fig. 2
Fitted linear broken-line plots of the average apparent total tract digestibility (ATTD) of P in diets as a function of phytase inclusion level. The optimum concentration of phytase determined by linear broken-line model was 1,215 (SE = 328.1) units of microbial phytase (FTU)/kg of feed; [Y = 72.1 − 0.035 × (1,215 − X)] where X is less than 1,215, with r2 = 0.932 and P < 0.05. The SE for the estimates of the intercept and second parameter were 3.55 and 0.012, respectively