An experiment was carried out to study the immune response and ileal microflora in broilers fed wheatbased diet with or without enzyme Endofeed W (EEW) and supplementation of thyme essential oil (TEO) or probiotic PrimaLac® (PP). Hypersensitivity, antibody production, haematology and immune organ weights were considered as the immune response and Lactobacillus, Bifidobacterium, and Escherichia coli were enumerated in ileum. A 2×3 factorial arrangement with two levels of EEW (0.0 and 0.05%) and two types of growth promoters (unsupplemented or supplemented with TEO or PP) was designed. Each of the six dietary treatments was fed to four groups with 12 chicks each from 0 to 42 days. Addition of EEW, TEO or PP to the wheat-based diet improved (P<0.05) immunity in terms of hypersensitivity response and heterophil to lymphocyte ratio as compared to the control group. Antibody production against sheep red blood cells (SRBC) antigen and other haematological analysis were numerically (P > 0.05) enhanced by the addition of EEW or TEO to diet, whereas total and IgG anti-SRBC altered significantly with administration of PP and white blood cells count was increased (P < 0.05) by the inclusion of growth promoters (TEO or PP) to the control diet. All feed additives induced competitive exclusion efficiently, in terms of increase (P< 0.05) in Lactobacillus and Bifidobacterium and reduction (P < 0.05) in E. coli counts.

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