The efficacy of recombinant equine follicle stimulating hormone (reFSH) to promote follicular growth in mares using a follicular suppression model.

This study examines the effects of a new single chain recombinant equine follicle stimulating hormone (reFSH) in stimulating follicle growth in mares, taking into account estrus syncing and hormonal suppression conditions.

Methodology

• The research involved 15 mares in breeding season. Their estrus cycles were synched using prostaglandin F(2alpha) or PGF(2alpha).
• Starting the day after ovulation, the mares were treated daily with progesterone and estradiol (P&E) for two weeks.
• PGF(2alpha) was re-administered on day 6 of the synced estrus cycle to induce luteolysis (the degradation of the corpus luteum, a structure that develops in the ovary after ovulation).
• The mares were then divided into three groups and began treatment on the eighth day after ovulation.
• Two groups were given small or large doses of reFSH, while the control group received saline. All treatments were administered intravenously twice a day concurrently with the final week of P&E treatment.
• When a follicle or group of follicles reached 35mm in diameter, the mares were given recombinant equine luteinizing hormone (reLH) to stimulate ovulation.

Measurements and Observations

• Blood was sampled each day to measure for FSH, LH, estradiol, progesterone, and inhibin using a method called a radioimmunoassay (RIA).
• On the first day of reFSH or saline treatment, periodic blood samples were collected for six hours post-injection to check for changes in FSH concentration.
• Ultrasonography and a stallion were utilized to monitor daily follicular activity, estrus, and ovulation.

Results

• A significant increase was observed in the diameter of the largest follicle in reFSH-treated mares compared to controls, from treatment end day till day 21 post-ovulation.
• reFSH-treated mares developed more follicles of sizes within the ranges of 20-29mm, 30-34mm, and above or equal to 35mm.
• Mares receiving reFSH treatment generated 2-3 times more pre-ovulatory follicles in a shorter time than control mares.
• Despite reFSH treatment resulting in more follicular growth, the number of successful ovulations in treated and control mares remained similar due to increased incidence of ovulation failure in the treated group.
• Mares treated with reFSH showed higher concentrations of plasma FSH, inhibin, and estradiol compared to controls. Meanwhile, their plasma LH concentrations were suppressed and did not exhibit the ovulatory surge of controls.

Conclusion

• The study proved that using the novel reFSH increases the number of total and pre-ovulatory follicles in mares where natural pituitary gonadotropins are suppressed.
• The use of reFSH was found to be efficacious in promoting the development of more pre-ovulatory follicles, even when the mares were undergoing a regimen of P&E that suppressed follicular growth.