This study was carried out to evaluate the effects of different levels and sources of oregano leaf in starter diets for broilers. The 10 different dietary treatments included 1) a nonsupplemented corn-soybean meal diet (negative control); 2) the basal diet + 55 mg/kg of penicillin (positive control); 3 to 6) 2.5, 5.0, 10.0, and 20.0 g of oregano of Mexican origin/kg of diet; and 7 to 10) 2.5, 5.0, 10.0, and 20.0 g of oregano of Mediterranean origin/kg of diet, respectively. Each diet was fed to 6 replicate pens of 5 male birds in battery brooders for 18 d. Broiler chicks fed diets containing penicillin had higher BW at 18 d and improved FE from 1 to 18 d of age compared with those fed the negative control diet or those fed different levels of oregano leaf of both origins. In addition, different levels of oregano leaf had no effects on BW, FCR, or mortality rate. Birds fed the diet with 20.0 g/kg of oregano of Mediterranean origin were intermediate in feed conversion to birds fed the negative and positive control diets. Higher levels of oregano than used in this study in a more challenging rearing environment may be needed to elicit a stronger positive response to oregano leaf in broiler diets.
