Reproductive seasonality in the mare: neuroendocrine basis and pharmacologic control.

This research investigates the seasonal reproduction patterns in mares, mainly revolving around hormonal activity and potential pharmacological interventions. The most important influencing factor noted is the variation in daylight, which impacts synthesis and secretion of a certain hormone known as LH, subsequently affecting ovarian cycles in mares. The paper explores the use of a specific type of hormone, GnRH, for potential control over these cycles, but highlights the need for a commercially suitable delivery method.

Understanding Reproductive Seasonality in the Mare

• The research discusses how the reproductive cycle in mares is impacted by seasonal changes, with the most influential determinant being day length. As the days shorten with the approach of autumn, there’s a marked decline in the synthesis and secretion of LH (luteinizing hormone). This hormonal shift halts the ovarian cycles in most mares by winter solstice.
• The synchronization of endogenous reproductive rhythms in mares, like many other seasonal animals, comes as a response to periodic cues from the environment, with light exposure playing the main role. Supplemental lighting schemes have been utilized for many years as a management tool to modify the timing of reproductive cycles in these animals.

The Role of Neuroendocrine Signals

• The study has sought to understand the biological foundations of these seasonal rhythms, with a particular focus on the roles of different synaptic and humoral signalling pathways, especially those related to GnRH (gonadotropin-releasing hormone), and their impact on the reproductive behavior in mares.
• Recent attention has been given to a new neuropeptide identified as RF-related peptide 3 (RFRP3). This peptide has the potential to inhibit GnRH secretion or alter gonadotrope responsiveness, though the results have been varied across different mammalian females and null in the mare.

Pharmacological Intervention and Future Prospects

• Despite ongoing research gaps, the researchers highlight that the necessary knowledge to pharmacologically control seasonal anovulation (non-occurrence of ovulation) has existed for over two decades. The continuous infusion of native GnRH is identified as a reliable and efficient mechanism for accelerating reproductive transition, uniquely applicable to horses.
• However, the authors point out that its practical application has not been realized due to the absence of a suitable and commercially acceptable delivery vehicle for GnRH, implying an area of focus for future research and development.