Unraveling ovarian histology: The key morphological aspects that spur the development of the Fossa ovarii in equine.
Abstract: 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.
© 2026 The Author(s). The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.
Publication Date: 2026-01-16 PubMed ID: 41542794DOI: 10.1002/ar.70131Google Scholar: Lookup
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- Journal Article
Summary
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Overview
- This study investigates the unique structural development of the equine fetal ovary, particularly focusing on how the ovulation fossa forms during gestation.
- The research tracks the histological changes in fetal ovaries from early to late gestation, providing insights into when and how key ovarian features emerge.
Introduction to Equine Ovarian Structure
- The equine ovary is distinct compared to other domestic species, mainly because of:
- Its ovulation fossa, a specialized groove where ovulation occurs.
- An inversion of the usual cortical (outer) and medullary (inner) ovarian layers seen in most species.
- Understanding these features is important for insights into equine reproductive biology and health.
Study Objectives
- To investigate the morphostructural (shape and cellular) development of the fetal equine ovary during different stages of gestation.
- To emphasize the formation process of the ovulation fossa, which is unique to horses.
Methodology
- Sample collection:
- 14 female equine fetuses were collected from a commercial abattoir.
- Gestational ages ranged from 70 to 200 days, covering early to late fetal development.
- Histological examination involved studying tissue morphology including cells and overall ovarian structure changes.
Key Findings
- Ovarian growth:
- There was a noticeable increase in ovarian volume as gestation progressed.
- Histological changes included:
- Proliferation (increase) of interstitial cells, which are supporting cells within the ovary.
- Organization of germ cells into ovigerous cords, which are clusters of cells that will develop into eggs.
- At the site where the ovulation fossa develops:
- There was cortical thickening (outer layer becoming thicker).
- Surface invagination (an inward folding of the ovary surface) was observed.
- However, important adult ovarian features were absent during fetal development:
- No cellular differentiation indicative of full ovulation fossa maturation.
- No inversion of cortical and medullary layers, which in adults is a key characteristic.
Interpretation and Conclusions
- Initial histological signs of the ovulation fossa appear before birth, meaning the foundation starts during fetal development.
- Complete formation of the ovulation fossa, including cortical-medullary inversion and cellular differentiation, seems to occur after birth.
- The findings enhance understanding of ovarian development in horses, offering a baseline for future research.
- This knowledge has implications in areas such as:
- Horse reproductive physiology.
- Diagnosis and study of ovarian pathologies.
- Improved management of equine breeding and reproduction.
Significance of the Study
- Gives detailed temporal and morphological information about an unusual equine ovarian feature.
- Fills gaps in knowledge about fetal ovarian development in horses, a less-studied domestic species.
- Provides histological data that could help interpret developmental abnormalities or fertility issues involving the ovulation fossa.
Cite This Article
APA
Ver Goltz L, Gomes SP, Schimming BC, Abdala FCM, Miglino MA, de Castro Sasahara TH.
(2026).
Unraveling ovarian histology: The key morphological aspects that spur the development of the Fossa ovarii in equine.
Anat Rec (Hoboken).
https://doi.org/10.1002/ar.70131 Publication
Researcher Affiliations
- Departamento de Cirurgia, Setor de Anatomia dos Animais Domésticos e Silvestres, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo (USP), São Paulo, Brazil.
- Departamento de Cirurgia, Setor de Anatomia dos Animais Domésticos e Silvestres, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo (USP), São Paulo, Brazil.
- Departamento de Biologia Estrutural e Funcional, Instituto de Biociências, Universidade Estadual Paulista (UNESP), Botucatu, Brazil.
- Departamento de Cirurgia, Setor de Anatomia dos Animais Domésticos e Silvestres, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo (USP), São Paulo, Brazil.
- Postgraduate Program in Animal Health, Production and Environment, University of Marilia (UNIMAR), Marilia, Brazil.
- Departamento de Biologia Estrutural e Funcional, Instituto de Biociências, Universidade Estadual Paulista (UNESP), Botucatu, Brazil.
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