Evaluation of Different Levels of Canola Meal on Performance, Organ Weights, Hepatic Deiodinase Gene Expression and Thyroid Morphology in Broiler Chickens

Abstract

This study was carried out to determine the effects of dietary inclusion level of canola meal (CM) on performance, organ weights and hepatic type I deiodinase gene expression in broilers. A completely randomized design with 4 levels of CM (0, 10, 20 and 30%) as a substitute for soybean meal (SBM) was utilized with 5 replicates of 9 birds each. The results showed that body weight gain (1 to 42 d) decreased linearly (P<0.01) as the inclusion of CM increased. An increase in dietary level of CM also resulted in a linear (P<0.05) increase in feed conversion ratio (1 to 42 d). Proportion of thyroids (P<0.05) and liver (P<0.01) increased linearly with increased levels of CM. A significant linear increase in right ventricular weight: total ventricular weight ratio (P<0.01) and heart weight (P<0.05) were observed by substituting CM for SBM. The concentration of plasma triiodothyronine and triiodothyronine: tetraiodothyronine ratio decreased linearly (P<0.01) with increasing level of CM. Expression of hepatic type I deiodinase gene (D1) decreased linearly (P<0.01) as inclusion level of CM in diets increased. Moreover, increasing linear (P<0.01) and quadratic responses (P<0.05) were observed in follicles number and epithelial thickness in broilers thyroids followed by increased levels of CM. In addition, increases in dietary CM inclusion led to a linear (P<0.01) increase in thyroid follicles diameters. In conclusion, the results of this study indicate that feeding increasing CM inclusions from 0 to 30% negatively affect growth performance of broiler chickens. From this study, it can also be concluded that substitution of CM for SBM adversely interferes with thyroid and liver functions and decrease D1 gene expression, likely because of higher dietary concentration of glucosinolates.