Abstract
Background:
The reproductive biology of the Muscovy duck (Cairina moschata forma domestica) remains incompletely characterized, particularly regarding qualitative, cycle-dependent histological remodeling of the oviduct. While previous research has mainly focused on morphometric measurements, detailed descriptions of epithelial organization, mucosal folding, and cellular composition across reproductive stages are limited.

Aim:
This study aimed to qualitatively characterize histological changes in the oviduct of adult Muscovy ducks across different reproductive stages.

Methods:
Oviducts from 35 adult female Muscovy ducks representing non-laying, laying, and brooding stages were examined using routine histological techniques. Segment-specific epithelial architecture, mucosal folding, and cellular composition were assessed along the infundibulum, magnum, isthmus, uterus, and vagina.

Results:
Segment-specific epithelial architectures were observed throughout the oviduct. Proximal segments (infundibulum, magnum, and isthmus) showed pronounced morphological plasticity across reproductive stages, whereas distal segments (uterus and vagina) remained comparatively stable. In the magnum and isthmus, epithelial morphology was heterogeneous during the non-laying phase, became more uniform during laying, and simplified during brooding. In contrast, the uterus and vagina exhibited minimal structural changes. Mucosal folding displayed regional and stage-dependent variation, with consistently strong folding in the infundibulum and notable changes in the magnum and uterus. During the non-laying stage, the epithelium was mainly pseudostratified columnar with basal, goblet, and ciliated cells, while the vagina showed a stratified epithelium. During laying, the magnum and isthmus became more homogeneous with increased goblet cell activity. During brooding, the magnal epithelium simplified and was dominated by ciliated cells, whereas distal segments remained structurally stable.

Conclusion:
The Muscovy duck oviduct exhibits clear region-specific and reproductive stage-dependent histological remodeling, with greater epithelial plasticity in proximal segments and relative stability in distal regions. These structural changes likely reflect functional adaptations to shifting reproductive demands, where dynamic epithelial reorganization in the infundibulum, magnum, and isthmus may support processes such as oocyte capture, secretion, and egg component formation during active laying. Conversely, the relative stability of the uterus and vagina suggests a consistent role in egg transport and expulsion. Collectively, these findings provide new insights into the functional significance of oviductal mucosal remodeling and highlight its potential role in optimizing reproductive efficiency across different physiological stages.

Key words: Epithelial morphology; Histology; Mucosal folding; Muscovy duck; Reproductive cycle.