The effect of vaccination on the development of immune formations in the esophagus of turkeys

Vaccination of poultry provides protection against a range of bacterial and viral pathogens and depends on the development of immune structures within the digestive organs, where immune responses arise under the influence of antigens. These responses are manifested by the production of antibodies, the appearance of effector cells, and the formation of immunological memory specific to a given foreign agent. The aim of the present study was to examine the development of immune structures in the oesophagus and its dilated part – the crop – and to determine the timeline of their complete morphofunctional maturation in vaccinated and unvaccinated birds. For histological examination, material was collected from 66 Big-6 turkeys aged from 1 to 50 days, divided into an experimental (vaccinated) group and a control (unvaccinated) group. Classical histological staining methods were applied, including haematoxylin and eosin, Van Gieson, Mallory, and Weigert techniques, as well as silver impregnation with silver nitrate according to Kelemen. In vaccinated turkeys, immune formations in the oesophagus and crop were first observed at 20 days of age and were represented by local aggregations of diffuse lymphoid tissue, with the crop also containing pre-nodular structures. These formations were located beneath the epithelial layer in the lamina propria of the mucosa, within the submucosa, near the oesophageal glands, and directly within the glandular tissue. Migration of lymphoid cells into the lower layers of the epithelium was observed from the surface of these aggregations. By 30 days of age, the lymphoid tissue in this group was morphofunctionally mature, with the presence of lymphoid nodules both with and without germinal centres. In unvaccinated turkeys, immune structures in the oesophagus and crop were first detected at 30 days of age and were represented by diffusely distributed lymphocytes. Morphofunctional maturity of these structures, indicated by the presence of all levels of lymphoid tissue organisation, was observed at 40 days of age. The obtained results are of practical importance and should be considered during the planning and implementation of prophylactic and therapeutic measures in turkey rearing