Light and Electron Microscopic Examination of the Cervical Portions of the Esophagus in the Muscovy Duck (Cairina moschata)

Objective: The esophagus in poultry serves as a primary conduit for food transport and, in many species, a specialized organ for temporary storage and conditioning. This study aimed to elucidate the anatomical, histological, and surface ultrastructural features of the esophagus and crop in the Muscovy duck, focusing on regional specializations related to its feeding ecology. Materials and Methods: Tissue samples were collected from ten healthy adult Muscovy ducks across three distinct regions: the cervical esophagus (Region 1), the crop (Region 2), and the post-crop esophagus (Region 3). The samples were processed for light microscopy (H&E and PAS staining) and scanning electron microscopy (SEM) to evaluate the mucosal architecture and glandular distribution. Results: Histological examination revealed that the entire esophageal tract is lined with a protective stratified squamous epithelium. A significant regional variation was observed in the density of esophageal glands, which were markedly more abundant in Region 1, suggesting an intensive lubrication requirement during the initial stages of deglutition. In the crop (Region 2), the tunica muscularis was notably thinner, facilitating the organ's expansion for food storage. A unique finding was the close anatomical association between the mucosal glands and lymphoid follicles, indicating a specialized local immune barrier. SEM analysis demonstrated intricate microridge patterns on the epithelial surface of transport zones, whereas the crop exhibited prominent glandular openings and a dense mucociliary network designed for food softening. Conclusions: The findings indicate that the Muscovy duck esophagus is a morphologically dynamic organ with distinct regional adaptations. The high glandular density and robust lymphoid presence highlight a dual specialization for both efficient food processing and mucosal defense, reflecting the evolutionary requirements of a surface-feeding waterfowl.