Oviduct Histopathology of Internal Laying and Egg-Bound Syndrome in Laying Hens

SIMPLE SUMMARY: Internal laying and egg-bound syndromes are avian reproductive disorders that reduce egg productivity in laying hens. To date, the understanding of the importance of peristalsis abnormality in the smooth muscle of oviducts has been focused on the pathogeneses of internal laying and egg-bound syndrome, and the histopathology of the oviductal epithelium has not been explored. In this study, we histologically examined the oviductal ciliated epithelium of aged laying hens. We observe that the epithelial region lacking cilia is larger in the oviducts of hens with internal laying and egg-bound syndrome than in those of healthy hens. In addition, the lamina propria of the oviducts of hens with internal laying and egg-bound syndrome is affected by the infiltration of CD3-positive T-cells. The histological alternation of the ciliated epithelial cells in the oviducts owing to the oviductal inflammation is suggested as the underlying cause of the pathogeneses of internal laying and egg-bound syndrome. ABSTRACT: In the egg industry, common reproductive disorders, such as internal laying and egg-bound syndrome, not only reduce egg productivity but also cause deaths in severe cases. In this study, we focused on the oviduct histology of the pathogenesis of internal laying and egg-bound syndrome. We divided the aged laying hens into four groups according to the observation of the abdominal cavity and oviductal lumen: healthy, internal laying, egg-bound, and intercurrent. The percentages of healthy, internal laying, egg-bound, and intercurrent groups were 55%, 17.5%, 15%, and 12.5%, respectively. In all parts of the oviduct (i.e., infundibulum, magnum, isthmus, and uterus), the oviductal epithelium was composed of ciliated epithelial cells and secretory cells. The epithelial region lacking cilia was larger in the entire oviduct of the internal laying, and intercurrent groups than in the healthy group. In the internal laying, egg-bound, and intercurrent groups, significant T-cell infiltration was observed in the lamina propria of the entire oviduct. The morphological alteration of ciliated epithelial cells in the oviducts caused by inflammation may be the underlying cause of the pathogenesis of internal laying and egg-bound syndrome.