Gonadotropin releasing hormone (GnRH) affects precopulatory behavior in testosterone-treated geldings.

The research paper puts forward an investigation on the effects of Gonadotropin releasing hormone (GnRH) on pre-mating behaviors in geldings (castrated male horses), particularly those supplemented with testosterone. The findings propose that GnRH, in the presence of testosterone, can significantly alter key pre-copulation behaviors.

Methodology of the Study

• The study was designed using twelve pony geldings, split into two groups based on whether they were treated with testosterone replacement or not. Testosterone replacement represents a dose of 200 micrograms/kg of testosterone propionate in oil, administered subcutaneously every 48 hours.
• Within each of these two core groups, subjects were further divided based on whether they received Gonadotropin releasing hormone (GnRH; at a dose of 25 micrograms, delivered subcutaneously every three hours) or merely a control treatment.

Observational Criteria

• Researchers observed sexual behavior during a four-minute exposure to a mare in estrus (heat), three times each week for two weeks before treatment, three weeks during treatment, and three weeks after the treatment was stopped.
• The sexual behaviors specifically looked at consisted of the flehmen response (a behavior in which the animal curls back its upper lip and inhales), attention duration, vocalization frequency, and erection duration.

Findings

• Among geldings treated with both testosterone and GnRH, there was a notable increase in flehmen response frequency and attention duration, as well as a decrease in vocalization frequency and erection duration, in contrast to geldings that received testosterone alone.
• In geldings not supplemented with testosterone, it was observed that GnRH did not provide a detectable effect on sexual behavior.

Conclusion

The researchers concluded that the results support an hypothesis of a testosterone-dependent, central-nervous-system-mediated impact of GnRH on pre-mating behavior in stallions (adult male horses). These results can aid in better understanding of animal behavior and may have potential implications in domestic and wild horse management.