Anatomical and histological insights into gastrointestinal adaptations of adult Egyptian quail.

Coturnix coturnix is widely used as a laboratory model due to its small size, ease of care, and rapid maturation. This study examined the relationship between the structure of its alimentary tract and feeding habits using anatomical, morphometric, histological, histochemical, and ultrastructural analyses. The stomach comprised a glandular proventriculus and a muscular gizzard, while the ileum was the longest intestinal segment. Paired, well-developed caeca were present at the ileocecal junction. Histologically, the alimentary canal showed the typical four layers: mucosa, submucosa, muscularis, and serosa. The proventriculus contained superficial tubular glands in the lamina propria and deeper compound glands in the submucosa. The gizzard featured a thick keratinoid koilin layer and three smooth muscle layers. The intestinal mucosa formed spatula-shaped villi, with goblet cells increasing in number toward the caecum. Histochemical analysis revealed positive PAS and Alcian Blue reactions in the proventriculus, koilin layer, intestinal epithelium, and goblet cells, indicating the presence of neutral and acidic mucins. Bromophenol Blue staining confirmed protein content in the intestinal epithelium and lamina propria, while Masson's Trichrome demonstrated collagen distribution in connective tissues. Ultrastructurally, proventricular cells showed abundant secretory granules, rough endoplasmic reticulum, and mitochondria. The gizzard exhibited well-developed muscle fibers, and the intestinal epithelium displayed microvilli and junctional complexes, supporting efficient digestion and absorption. These findings highlight the structural adaptations of the digestive tract in relation to functional demands.