Effect of dietary dexamethasone on the morphologic and morphometric adaptations in the lymphoid organs and mortality rate in broilers.

Background: Thymus, bursa of Fabricius and spleen are the major lymphoid organs of avian species that plays a crucial role in their immunity. Though glucocorticoids are reportedly used as growth promoters, they also suppress the immune system. Objectives: The objective of this study was to investigate the morphologic and morphometric adaptations in the lymphoid organs as well as the mortality rate in broilers in response to long‐term treatment with dexamethasone (DEX). Methods: A total of 80 one‐day‐old broiler chicks (Cobb 500) were randomly divided into four homogenous groups (control – C and treatment groups – T1, T2, and T3). The treatment groups received DEX at the rate of 3, 5, and 7 mg/kg commercial feed. Samples, i.e. thymus, bursa of Fabricius, and spleen, were collected on 7, 14, 21, and 28 days of the experiment. Relative weight of the organs was calculated on each sampling day. The tissues were then processed and stained with haematoxylin and eosin stain for morphological and morphometric study. Results: The relative weight of lymphoid organs was found substantially (p < 0.05) less in the DEX‐treated groups. Significant (p < 0.05) reduction in lobular size and the cortical‐medullary ratio was observed in the thymus of the DEX‐treated broilers. Follicular atrophy and massive depletion of lymphocytes were evident in the bursa of Fabricius. The mortality rate was also increased which was largely dependent on the dose and duration of DEX treatment. Conclusions: The study results indicate that DEX treatment can alter the morphology and morphometry of lymphoid organs which might result in severe immunosuppression and increased mortality rate in broilers. [ABSTRACT FROM AUTHOR]