Crop Morpho-Histological Peculiarities in Domesticated Pigeons (Columba livia domestica), Cattle Egret (Bubulcus ibis) and Domesticated Ducks (Anas platyrhynchos domestica)

Abstract

The crop architecture varies among different avian species consistent with their feeding habits. Therefore, twenty-one of mature healthy male pigeons (granivorous), cattle egrets (carnivorous), and ducks (omnivorous), seven per species, were utilized for the histological, immunohistochemical, and ultrastructural analyses. Histologically, the mucosal folds were covered by non-keratinized stratified squamous epithelium in the three investigated species. The mucosal glands are only peculiar to the crops of the cattle egrets as well as the ducks, while the pigeons' crops were devoid of any secretory units. Morphometrically, the optical densities of the Alcian blue (AB) and periodic acid Schiff (PAS) reactions in the secretory glands, the area % of collagen fibers, the thickness of the tunica musculosa were measured and declared significant differences among the three studied avian species. Immunohistochemical reaction revealed ki-67 immuno-positive reactivity in the nuclei of basal cell layers of the crop epithelium in pigeons only. Regarding ultrastructure investigation, the covering epithelium of all studied species had been shown to be the basal layer of cuboidal to tall columnar cells with desmosomal junctions at the level of their cellular interdigitation, intermediate layers of large irregular polygonal cells with obviously increased cytokeratin filaments especially in the ducks and cellular interdigitation in between. The superficial layer of flat-shaped cells in the three investigated species manifested by desmosomal junctions in between but at the level of the surface squamous cells of the superficial layer, a fine lateral process is only inspected in the pigeons. In conclusion, the crop glands characterized by supranuclear electron dense secretory granules in the cattle egrets and electron-lucent in ducks.