Effects of low doses of oestradiol, testosterone and dihydrotestosterone on the immune response of broiler chicks.

Administration of either 1 microgram kg-1 BW oestradiol 17 beta (E2), 0.1 mg kg-1 BW testosterone (T) or 0.2 mg kg-1 BW dihydrotestosterone (DHT) in feed to broiler chicks for 50 days caused increased serum concentration of the hormones compared to the control birds that were given no drugs. E2 and T but not DHT resulted in a significant decrease of the total number of leukocytes, lymphocytes and the weight of bursa of Fabricious. The hormones significantly reduced the macrophage phagocytic activity compared to controls. It is suggested that prolonged administration of low doses of E2 and T but not DHT to chicken may induce immunosuppressant effect.