Characterization of follicle populations in mare ovaries: From preantral to preovulatory follicles

Abstract

Introduction: The equine ovary is peculiar in that, unlike other mammalian ovaries, its germinal surface, where follicles and oocytes are found, is located at the organ’s central portion, while its conjunctive tissue and vessels are found in the external layer. The purpose of this study was to describe morphological and quantitative aspects of preantral and antral follicles in the equine ovary. Materials and Methods: Of the 189 mare ovaries evaluated, six were collected from necropsied mares and sliced lengthwise parallel to the ovulation fossa. The slices were fixed and processed for histological evaluation under light microscopy. Preantral follicles were classified according to developmental stage and as morphologically normal or degenerated. For the remaining 183 ovaries, obtained from an abattoir, antral follicles were measured, punctured and oocytes evaluated. Oocyte recovery rates were calculated for each follicle size category. A total of 490 preantral follicles were examined. Results: Primary follicles were in greater number than primordial follicles. No secondary follicles were found. A total of 518 antral follicles were punctured and evaluated. Total oocyte recovery rate was 47.6. Preantral follicles were scarce in the equine ovary. Conclusion: Oocyte recovery rate was higher for smaller-diameter antral follicles.