Morphological Analysis of the Digestive Tract of Cockatiels (Nymphicus hollandicus)—Oesophagus to Colorectum

Cockatiels (Nymphicus hollandicus) are birds present in several countries, commonly kept as pets and, therefore, are frequently encountered as patients in veterinary hospitals. Knowledge of the morphology of the cockatiel's digestive tract is essential for understanding its digestive problems and clinical care. The objective of this study is to describe the digestive tract morphology of these birds. Six cockatiels were dissected and all parts of the digestive tract were measured and processed for histological analysis. The measured data were highly variable for some parts. The oesophagus is divided into a cervical part with the ingluvies (crop) and celomic portion. Mucosal folds and a stratified non-cornified epithelium in the oesophagus and ingluvies were observed. No oesophageal glands were observed in the cervical portion and ingluvies, however, in the celomic portion submucosal glands were abundant. The cockatiel's stomach is subdivided into a glandular and a muscular part. The glandular stomach has a simple columnar epithelium with PAS+ cells and gastric glands. The muscular stomach exhibits a gastric cuticle, and simple columnar epithelium with branched tubular glands, and its muscular layers are organised in inner circular and outer longitudinal bundles. The intestine of cockatiels is subdivided in the small intestine with duodenum, jejunum, ileum and the short large intestine is represented by the colorectum. The Tunica mucosa of the small intestine forms villi lined with simple columnar epithelium with goblet cells. Simple tubular glands extend into the lamina propria mucosae. The wall of the large intestine contains simple tubular glands and a circular and thin layer of smooth muscles. Despite the absence of lymph nodes, there are numerous lymphocytes in the lamina propria. The digestive tract and histological characteristics observed are consistent with other avian species, however, well-defined species-specific particularities were observed.