The effects of different dietary levels of olive leaf powder (OLP) as a natural antioxidant on growth performance, carcass traits, some blood parameters, small intestinal morphology and feed digestibility in broiler. A total of 300 one-day-old Cobb500 broilers were studied in a completely randomized design with 5 treatments, 3 replicates and 20 chicks for each replicate, up to 42d. The experimental diets included: corn-soybean meal basal diet (negative control), basal diet supplemented with 250 mg/kg of alpha-Tocopheryl acetate (positive control) and three basal diets containing 2, 2.5 and 3 percent OLP. The results showed that during total experimental period (1-42d), weight gain decreased (P<0.05) in OLP groups in comparison to the positive control. Feed intake during 1-42d period was lower (P<0.05) in the group which was treated by 3 percent OLP in comparison to the positive control group. In starter period, feed conversion ratio increased (P<0.05) in all groups treated by OLP in comparison to negative and positive controls. Dietary inclusion of different levels of OLP increased (P<0.05) length of villi, crypt depth and villus surface in comparison with the negative or positive controls. A significant decrease (P<0.05) was observed in serum concentrations of the triglycerides, cholesterol and low-density lipoproteins in OLP treated groups in comparison to negative or positive controls. Based on the results, dietary inclusion of OLP (up to 2 percent) in the broiler diets is recommendable, because it reduces blood lipids and also improves intestinal morphology.

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