Interrelationships among follicles during the common-growth phase of a follicular wave and capacity of individual follicles for dominance in mares.

This research examined the relationship and growth rate of follicles in mares, suggesting that the first follicle to emerge usually maintains dominance unless it is removed, in which case the second-largest follicle can take over.

Methodology

• The researchers observed 59 mares over a period following ovulation. They removed follicles with a diameter equal to or larger than 6.0 mm ten days after ovulation and tracked the growth of the four largest follicles.
• The follicles were ranked from D1 to D4, with D1 being the largest in diameter at the expected beginning of deviation (anything larger or equal to 20mm). They were also ranked as E1 to E4, depending on the order in which they emerged at a diameter between 6.0 to 6.9 mm.
• The emergence period of the follicles was recorded, and deviation began approximately 6.5 days after initial observation.

Findings

• The study found that the first follicle to emerge, E1, became the largest follicle in 61% of cases. This was significantly more than E2 (25%), E3 (9%), and E4 (5%).
• There was no difference in the growth rates among all four follicles throughout the common-growth phase, which averaged at 2.8 mm/day.
• Differences in diameters between follicles E1 and E2 three and six days after ablation were similar, indicating consistent growth patterns.
• When a larger follicle was removed, the largest remaining follicle became dominant in 76% of observations. If the largest follicle was ablated one or two days after the beginning of deviation, the second-largest follicle became dominant in 67% of instances.

Conclusions

• The researchers concluded that the first follicle to emerge typically retains its diameter advantage and dominance, and that all follicles exhibit similar average growth rates.
• They suggested a hypothesis – that all the four largest follicles at the beginning of deviation have similar potential for dominance, but a smaller follicle is unable to dominate if a larger follicle is present.
• The ability for the second-largest follicle to become dominant, in most cases, continues for up to two days after the beginning of deviation.