In order to estimate the crude protein (CP) equivalence value of Natuzyme-p (NP) enzyme by using regression response equations, two experiments were carried out using Ross (308) broiler chicks. Graded levels of dietary CP (while amino acids levels were kept constant) and NP enzyme were used to derive the regression equation in the first experiment. Four levels of dietary CP and NP enzyme were fed to 160 feather-sexed male broiler chicks during the starter (0-28 d of age) and grower (28-42 d of age) period. Each diet was offered to four replicates of five chicks in a completely randomized design. Results obtained in experiment one failed to fit a regression equation between BW, dietary CP levels and NP enzyme. In experiment two, graded levels of CP changed along with the levels of lysine (Lys), Met+Cys and threonine (Thr). Regression equations between BW and dietary CP and NP enzyme were derived. Nonlinear and linear equations were generated for enzyme and CP. Based on an assessment of r and P value, nonlinear equations were used to determine enzyme equivalence. The derived regression equations of body weight for CP were set to be equal with those obtained for NP and were solved; enzyme equivalence value for CP was calculated by subtracting the obtained value from CP content of basal diet. Crude protein equivalence value of NP at 28 and 42 d of age was estimated to be 0.96 and 0.38 %, respectively.
