Effect of the stage of the oestrous cycle on the follicular population in pony mares.

This article investigates how the stage of the oestrous cycle in pony mares impacts the population of their follicles. It concludes that the number and health of follicles varied depending on the day of the oestrous cycle, with certain stages exhibiting more large and healthy follicles.

Methodology

• The study was conducted during the middle of the breeding season on 16 pony mares, four each day, on four different days of the oestrous cycle (days 6, 14, 17, and the preovulatory day). Day 0 was taken as the day of the last ovulation.
• The researchers performed histological examinations on all the ovaries. They then studied the number, size, and atresia (identified by granulosa cell pyknosis) of all follicles larger than 1 mm in diameter using a Kryotome-video recorder-TV system.

Findings

• The follicular distribution across various sizes (1-5 mm, 5-10 mm, and greater than 10 mm in diameter) was similar in the right and left ovaries.
• The ovary with a luteal structure had fewer healthy follicles larger than 10 mm when compared to the other ovary.
• On day 6, all follicles larger than 10 mm in diameter were atretic. By day 14, however, the number of normal follicles larger than 10 mm increased significantly.
• Although the size of the largest normal follicle increased from day 14 to day 17, the number of follicles undergoing early atresia also increased significantly.
• Aside from the large preovulatory follicle, all follicles larger than 10 mm were atretic just before ovulation.
• A relationship was found between the follicular population and the length of the follicular phase. There was a high correlation (R = -0.56; P less than 0.02) between the number of normal follicles 1-10 mm in diameter and the length of the follicular phase.

Conclusion

• The research indicates that the health and quantity of follicles in the ovaries of pony mares fluctuate with the stages of the oestrous cycle, with different stages either enhancing or diminishing follicle health and numbers.