Comparative study between pony mares and ewes evaluating gonadotrophic response to administration of gonadotrophin-releasing hormone.

The research article compares the hormonal responses between pony mares and ewes when given a hormone-related treatment. It finds that mares continue to respond effectively to the treatment, but ewes show a decrease over time, implying a unique hormonal system in mares.

Study Objective and Methodology

• The research was conducted to compare the hormonal responses between pony mares and ewes in their LH (luteinising hormone) secretory patterns when subjected to GnRH (gonadotrophin-releasing hormone) treatment.
• Dioestrous mares and ewes (reproductive phase where the female is not receptive to mating) were injected with GnRH continuously for 15 hours.
• Simultaneously, ovariectomized mares and ewes, primed with progesterone, were subjected to either pulsatile (in regular pulses) or continuous GnRH for 5 days.

Findings in Mares

• Mares that received continuous GnRH had a continued LH secretion, signifying positive hormonal response. This effect was noted irrespective of whether the GnRH was administered in a pulsatile pattern or continuously for 5 days.
• The elevated plasma LH concentrations by day 5, and the absence of difference in mean LH concentrations and time-response curves, underscore a sustained response to GnRH treatment.

Findings in Ewes

• Contrary to mares, the LH concentrations in ewes initially increased after treatment, then declined and remained low. This pattern implies a possible GnRH receptor desensitization or downregulation, leading to reduced hormonal response over time.
• Further, ewes treated with continuous GnRH exhibited LH secretory patterns indicative of GnRH receptor downregulation as early as day 1 of treatment.
• No significant difference was observed in the LH concentrations in ewes treated with pulsatile GnRH as compared to controls.

Conclusion

• The study concluded that pony mares showed a continuous response to GnRH treatment, irrespective of the method of administration (pulsatile and continuous).
• On the other hand, ewes treated with continuous GnRH experienced a reduced LH secretion over time, which hints at a unique hypothalamic-pituitary axis operation in pony mares when compared to ewes.