Continuous infusion of gonadotrophin-releasing hormone (GnRH) advances the onset of oestrous cycles in thoroughbred mares on Australian studfarms.

This research article investigates the impact of continuous gonadotrophin-releasing hormone (GnRH) infusion on hastening the onset of oestrous cycles in thoroughbred mares found on Australian studfarms, ultimately advancing their fertility period.

Objective of the Study

• The main goal of this research is to demonstrate how the continuous infusion of Gonadotrophin-releasing hormone (GnRH) could potentially advance the start of oestrous cycles in thoroughbred mares who are anoestrous (inactive sexually) during a seasonal period.
• The study also aims to transit the use of this treatment method from controlled experimental conditions to real-world commercial applications on Thoroughbred stud farms in Australia.

Methodology

• The hormone, GnRH, was introduced subcutaneously to the mares through osmotic minipumps (OMP) at dose rates of 100 ng/kg/h and 200 ng/kg/h.
• Equine ovaries were examined on the day of OMP insertion and blood samples were taken twice a week from a portion of mares in the study for analysis of plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone levels.

Findings

• The research demonstrated that mares treated in this way showed a significantly short span from the commencement of GnRH infusion to the first ovulation, compared to untreated mares.
• The time span to first ovulation following GnRH treatment was also found to correlate negatively with the total volume of the ovary and the diameter of the largest follicle at the onset of the treatment.
• The GnRH infusion triggered an immediate rise in plasma LH concentrations which peaked during ovulation.
• Progesterone profiles showed that the induced corpus luteum – the temporary endocrine structure involved in ovulation and early pregnancy – had a normal lifespan and intact progesterone-secreting capability.
• The study also found a significant increase in the mean areas under the LH and FSH response curves in treated mares compared to control mares.

Conclusion

• The study concluded that continuous infusions of GnRH induced ovulation in a significant proportion of seasonally anoestrous mares on commercial Thoroughbred stud farms, thus potentially offering a viable method to advance fertility periods in thoroughbred mares.