Substitution of Soybean Meal with Canola Meal either with or without Exogenous Enzymes: Influence upon the Growth Performance, Carcass Characteristics and Plasma Thyroid Hormone Concentrations

Three hundred and sixty broiler chicks (Ross 308) were employed in an experiment from 6 to 49 days of age to evaluate the effect of replacing canola meal for soybean meal either with or without enzyme supplementation. Dietary treatments included 5 substitution levels (0, 25, 50, 75 and 100%) at two enzyme concentrations of: 0 and 400 g/ton in a 5×2 factorial layout experiment. The enzyme mixture contained mainly ?-glucanase activity and to some extent xylanase activity. Data were analyzed in a completely randomized design. Body weight gain during 6 to 21d was significantly (P<0.05) reduced by raising of canola meal substitution level and while enzyme addition successfully restoring the situation so that main effect of enzyme addition was observed as significant (P<0.05). However, body weight gain during 6 to 49d was not affected by treatments (P>0.05). The effect of substitution level was significant with respect to feed intake during the starting (6-21d) and growing (21-42d) periods whereas it was not significant during the finishing (42-49d) period and the entire the experiment (6-49d). Feed conversion ratio was significantly (P<0.05) influenced by substitution level in all the feeding periods. Main effects and interaction of treatments were not found significant for carcass traits and plasma thyroid hormone concentrations. Feed cost per unit of gain was linearly reduced by increasing the proportion of Canola Meal (CM) at the cost of SBM in the diet. Enzyme addition did not significantly affect feed cost per unit of gain. The optimal substitution level in terms of feed cost per unit of gain was 100%.