An experiment was conducted to estimate standardised ileal threonine (SID Thr) equivalency of a commercial multi-enzyme and its effects on broiler chick’s performance. The 10 treatments included a basal diet containing 0.56% and 0.46% SID Thr in starter and grower periods; treatments 2 to 5 were supplemented with graded levels (0.07%, 0.14%, 0.21% and 0.28%) of L-threonine and treatments 6 to 10 were basal diet supplemented with 0.1, 0.2, 0.3, 0.4 and 0.5 g/kg of multi-enzyme. Supple menting diets with multi-enzyme significantly (P<0.01) improved the feed conversion ratio at 28 and 42 d of age. Multi-enzyme addition linearly increased body weight gain (P<0.05) at 28 d of age and the immune response (P<0.05) at 36 d of age. Breast, thigh and abdominal fat relative weights were not affected by supplementing the multi-enzyme. Nonlinear and linear equations were generated for the multienzyme and graded levels of threonine. Based on an assessment for the r 2 and P values of the equation, body weight gain, immune response and feed conversion ratio were sensitive measurements of responses to multi-enzyme addition. The nonlinear or linear response equation with the higher r 2 values for added L-threonine and the equation for added multienzyme were set to be equal and were solved. The body weight gain and feed conversion ratio responses from 0.5 g multi-enzyme per kg of diet at 28 and 42 d of age was therefore equal to 0.08%, 0.05%, 0.16% and 0.07% SID Thr, respectively, and the immune response from 0.5 g multi-enzyme per kg of diet was equal to 0.14% SID Thr.
