Unraveling ovarian histology: The key morphological aspects that spur the development of the Fossa ovarii in equine

The equine ovary exhibits unique structural and developmental features that distinguish it from those of other domestic species, including the presence of an ovulation fossa and an inversion of cortical and medullary layers. This study aimed to investigate the morphostructural development of the equine fetal ovary, with particular emphasis on the formation of the ovulation fossa. Fourteen female equine fetuses, ranging from 70 to 200 days of gestation, were collected from a commercial abattoir. Results revealed a progressive increase in ovarian volume and marked histological changes throughout gestation, including the proliferation of interstitial cells and the organization of germ cells into ovigerous cords. Although cortical thickening and surface invagination were observed at the presumptive site of the ovulation fossa, neither cellular differentiation nor cortical-medullary inversion-hallmarks of the adult ovary-were evident. These findings suggest that while initial histological differentiation of the ovulation fossa occurs prenatally, its complete formation likely takes place postnatally. This study contributes to a better understanding of ovarian development in horses and provides new data for future studies in areas such as physiology, pathology, and animal reproduction.