Follicle Diameter and Systemic Hormone Interrelationships during Induction of Follicle Collapse with Intrafollicular Prostaglandin E2 and F2α in Mares.

This research investigates if injecting prostanoids (PGE2 and PGF2α) within the ovarian follicle of mares could accelerate the follicle collapse process and also explores the differences in hormone features relating to natural and stimulated follicle collapses.

The Research Method

• Six mares were monitored for two oestrous cycles each. When a follicle diameter of 30-35mm and mild to moderate endometrial swelling were observed, a single 0.5 ml dose containing 500 μg PGE2 and 125 μg PGF2α was administered to the mares (treatment cycle) or a placebo (0.5 ml of water for injection; control cycle) into the preovulatory follicles (hour 0).
• Blood samples were taken and recurring ultrasound examinations were made up until the follicle collapsed.

Findings of the research

• The collapse of the follicles in treated mares happened significantly earlier (20.0 ± 5.9 hours) than in the control mares (72.0 ± 10.7 hours).
• No difference was observed in the concentrations of LH (Luteinizing Hormone), progesterone, total oestrogens, and oestradiol among both groups.
• But a noticeable rise in progesterone concentration occurred between 48 and 72 hours after the injection into the follicle in the treatment group compared to the control group.

Conclusion from the research

• The findings confirmed that the intrafollicular treatment with PGE2 and PGF2α accelerates the follicle collapse in mares, even without using an ovulation inducer.
• Despite the early induction of follicle collapse, the profiles of LH and oestradiol were unimpacted.
• This suggests that prostaglandins play a role in the process of the rupture and collapse of the follicle wall, thereby hinting at the possibility of this occurrence even prior to the sharp rise in circulating LH at the final stage of the ovulatory surge.

This research therefore provides invaluable insights into the influence of prostaglandins in the ovulation process in mares, particularly regarding the timing and characteristics of follicle collapse.