This study was conducted to assess the effect of whey powder and physical form of feed on humoral immunity and transcript abundances of interleukin-4(IL-4) and interferon-gamma (In-γ) genes on 240 Ross-308 day-old-chickens. The experiment was conducted in a completely randomized design in 6 treatments in factorial arrangement (2×3), whey powder at three levels (0, 4,8%) and physical form in two levels (mash, pellet) in broiler chicken diet with 4 repeats and 10 chickens per replicate. The diets formulated based on nutritional requirements of Ross strain-308 (2009) and were fed to the birds in three periods. To determine the immunity titer of ND, IBV, IBD and influenza blood samples were collected at day 10, 31 and 42. At the end of periods, one chicken was selected from experimental units and slaughtered; lymphatic organs were weighted and gene expression of IL-4 and In-γ measured after mRNA extraction and cDNA synthesis. It was found that the addition of whey powder did not have a significant effect on the weights of the spleen and bursa of Fabricius, but the pelleting in the growing stage had a significant effect on the weight of spleen (p<0.01). Pelleting and adding whey to diet in the growing period increased the IL-4 gene expression (p<0.05). In-γ expression was not influenced by whey powder, but pelleting increased its expression during the starter (p<0.01) and grower (p<0.01) stages.

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