Post-hatch Development of the Adrenal Gland in Chickens (<i>Gallus gallus domesticus</i>): Insights From Histology, Immunohistochemistry, Transmission Electron Microscopy, and Catecholamine Level Analysis

This study is the first to describe posthatching morphological changes in chicken adrenal glands using histology, immunohistochemistry, transmission electron microscopy, and catecholamine levels. The study involved 30 chickens in 3 posthatching stages: Juvenile (1 day old), immature (2 months old), and mature (6 months old). The results showed no demarcation between cortical and medullary, with the interrenal tissue comprising most of the adrenal parenchyma. The 1-day-old chickens did not exhibit the zoning of interrenal tissue into subcapsular and inner zones, while as they aged, the proportion of medullary tissue increased. The norepinephrine-secreting cells exhibited a significantly higher number of secretory granules compared to the epinephrine-secreting cells across the different stages. The plasma levels of catecholamines increased with advancing age. Chromogranin immunoactivity increased with age during the development of the adrenal gland. It can be concluded that the adrenal gland undergoes significant structural and functional changes during various posthatching developmental periods. In general, the study provides valuable insights into the growth and maturation of the adrenal glands in posthatch chickens, potentially aiding in understanding their maturation and their role in controlling catecholamines. In conclusion, the findings suggest that optimizing stress responses in chickens could enhance poultry production, potentially leading to the development of new stress management strategies.