Abstract: This experiment was conducted to evaluate the effects of additional supplementation of the diet with vitamin A, vitamin E and zinc, on blood cells, organ weights and humoral immune response of broiler chickens fed a wheat-soybean meal based diet. In a completely randomized design with 2×2×2 factorial arrangement, 224 day-old male broiler chicks were assigned to 32 groups. Factors and their levels were as follows: vitamin A (basal diet, basal diet supplemented with 10,000 IU kgG1 retinol acetate); vitamin E (basal diet, basal diet supplemented with 50 IU kgG1 \"-tocopherol acetate) and Zinc (basal diet, basal diet supplemented with 60 mg kgG1 Zn using zinc oxide). Sampling for blood and organ weights were done at 21 day of age. Humoral immune response were evaluated by intramuscular injection of Sheep Red Blood Cells (SRBC) at 21 day of age followed by bleeding at 7 and 14 day post injection. Supplementation of the diet with vitamin A, vitamin E, or zinc significantly (p = 0.001) increased the number of White Blood Cells (WBC); but had no effect on Red Blood Cell (RBC) counts, Hematocrit (Ht) and Haemoglobin (Hb). Vitamin A supplementation significantly (p = 0.016) decreased the proportion of monocytes in total number of counted monocytes, lymphocytes and heterophils. Supplementation with zinc significantly decreased (p = 0.003) the ratio of heterophils to lymphocytes. A significant vitamin A × vitamin E × zinc interaction was found for WBC counts and for the proportions of lymphocytes and heterophils (p = 0.001). Supplementing the diet with either vitamin A or vitamin E had no significant effect on relative weights of liver, bursa and spleen. However, addition of zinc to the diet significantly (p = 0.019) increased relative weight of spleen. Supplementation of the diet with vitamin E or zinc (but not with vitamin A), significantly increased total antibody titres against SRBC. The results suggest that additional supplementation of the diet with vitamin A, vitamin E, or zinc can be effective in general immune responses by affecting blood cell proportions and also indicated that zinc can be considered as an anti-stress nutrient, regarding the heterophil to lymphocyte ratio index. It also, indicates that vitamin E is more important than vitamin A or zinc in persistency of an immune response.

Keywords