highly significantP < 0.0001
The models were highly significant ( P < 0.0001), and the “Lack of Fit” of the models were not significant ( P > 0.05), which demonstrated the RSA and improved DMD were proper parameters representing the starch digestibility of the broilers, and the models were applicable to the optimization of exogenous carbohydrases for higher RSA and improved DMD in diets for the broilers.