Abstract
This study aimed to establish the effect of dietary supplementation in broiler chickens of organic and inorganic selenium on the weight and structure of the thymus, bursa of Fabricius and spleen. Three dietary regimes were studied in Flex and F15 Hubbard chickens: (i) control, (ii) diets containing 0.5 mg organic selenium/kg by selenized yeast, (iii) diets supplemented with 0.5 mg ionic selenium/kg (sodium selenite). The results showed that the feed additives did not affect the relative weight of the immune system organs, i.e. bursa of Fabricius, thymus and spleen. The organic selenium in the F15 resulted in thinning of the thymic cortex and partial depletion of the lymphoid cells. Moreover, both the organic and inorganic selenium supplementation resulted in depopulation of bursal medulla from lymphocytes in the F15 group. In contrast, in Flex chickens no significant differences in histological structure and morphometric values of lymphoid organs between chickens fed organic and inorganic selenium were found.