Comparative study of the oviduct of pre-laying and laying Egyptian balady ducks (Anas boschas domesticus) using morphometry, immunohistochemistry, scanning, and transmission electron microscopy

Egyptian balady duck (Anas boschas domesticus) is a breed of domestic duck native to Egypt of great economic importance. The present study investigated micromorphological, ultrastructural, and immunohistochemical aspects of the oviduct as well as serum estrogen and progesterone levels in pre-laying and laying Egyptian balady ducks. The oviduct comprised five segments: infundibulum, magnum, isthmus, uterus, and vagina. The mucosa was thrown into longitudinal folds throughout the oviduct, except for the vagina, where the folds appeared transverse. The folds were further split into secondary and tertiary folds. A significant age-associated increase in fold thickness was observed in the magnum and uterus. The surface epithelium appeared pseudostratified ciliated columnar, permeated by openings of the proprial glands. The secretory units of the proprial glands showed extensive branching in the magnum of laying ducks. Ultrastructurally, they revealed enhanced activity of Golgi apparatus and rough endoplasmic reticulum together with numerous spherical-shaped electron-dense granules in laying ducks compared to non-laying ones. Intracytoplasmic vacuoles were prominent in the surface epithelium, especially in the uterus, of pre-laying ducks and outnumbered those of laying ones. In contrast, the secretory cells of the surface epithelium appeared loaded with several electron-lucent granules concentrated toward their luminal side in laying ducks. CD3-immunoreactive T cells densely populated both the epithelium and lamina propria. A significantly higher presence of T cells was detected in the lamina propria than in the epithelium, regardless of duck age. Significantly higher serum estrogen and progesterone levels were detected in laying ducks compared to non-laying individuals, which may suggest a hormonal basis of the structural and ultrastructural differences between the two studied ages. The present study reported structural changes involving the oviduct associated with egg laying. This study improves the understanding of factors regulating avian oviduct health and productivity.