Gonadotropin-releasing hormone treatment induces follicular growth and ovulation in seasonally anestrous mares.

This research investigates the impact of gonadotropin-releasing hormone (GnRH) on the development of follicles and ovulation in standardbred mares that are seasonally anestrous, discovering that infusion of GnRH stimulates these processes quite effectively.

Introduction and Methodology

• The study aimed to test the efficiency of GnRH pulse infusion in instigating follicular growth and subsequent ovulation in standardbred mares experiencing seasonal anestrus (a period in which a female is not in a state of sexual receptivity and fertility).
• Seventeen mares with a previously normal reproductive history were selected and were kept under a photoperiod of 8 hours light to 16 hours dark, starting one week before the experiment.
• The study was initiated in the second week of January.
• The mares were divided into three groups: those that received 20 micrograms of GnRH/hour, those that received 2 micrograms of GnRH/hour, and mares that were only subjected to photoperiod treatment with no added hormones (control).

Results and Findings

• The serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone in the control group did not change. Neither did they show any notable follicular development or ovulation over the experimental period of 60 days.
• In contrast, the GnRH-treated groups showed a prominent rise in LH and FSH serum concentrations within just a day of starting the infusion.
• In the mare group treated with 20 micrograms of GnRH/hour, a follicle size of 25 mm or more was observed on average after approximately 7.4 days from the start of the infusion, and ovulation was recorded after an average of 12 days.
• On the other hand, the group treated with 2 micrograms of GnRH/hour showed a slightly quicker response with the presence of a 25 mm follicle detected typically after 5.7 days and ovulation after 10 days of treatment.
• After every ovulation, a functional luteal phase was observed, indicated by the patterns of progesterone secretion.

Conclusion

• The GnRH treatment resulted in follicular growth and induced ovulation, with higher doses leading to a slightly slower response than smaller doses.
• These results suggest that GnRH treatment effectively stimulates reproductive responses in seasonally anestrous mares.