The influence of photoperiod on gonadotrophin-releasing hormone stimulated luteinising hormone release in the anoestrous mare.

This study investigated how the length of daylight, or photoperiod, can influence the reproductive cycles in horses, particularly the transition from an inactive (anoestrus) to a receptive (oestrus) state for breeding. The researchers found that artificial extension of daylight could stimulate a faster response to gonadotrophin-releasing hormone, which plays a crucial role in triggering reproductive activities in the animals.

Objective and Methodology of the Research

• The researchers aimed to examine if extended daylength, either natural or artificial, could speed up horses’ response to gonadotrophin-releasing hormone (GnRH), a hormone that helps regulate reproductive processes.
• To do this, they monitored nine non-reproducing (anoestrous) mares that were subjected to either natural (ambient) or artificial long lighting starting January 7th over a four-month period.
• The experiment was structured in three-day sequences repeated every 21 days. On the first day of each sequence, the mares’ ovaries were assessed through rectal palpation. On the second day, a saline solution was given intravenously, while on the third day, GnRH was administered.
• Blood samples were collected at different time intervals after the saline or GnRH treatment and were analyzed to determine luteinising hormone (LH) levels, a helpful marker of reproductive activity.

Results and Implications

• The research showed that mares under artificial long light conditions responded to GnRH within six weeks, while mares under ambient lighting took approximately 12 weeks to show a similar response.
• This suggests that increasing the photoperiod can stimulate a quicker transition from aninactive to a receptive state for breeding in mares, potentially influencing the timing of reproductive cycles in the species.
• The reason for this accelerated response to GnRH could be due to several factors, such as changes in LH levels in the pituitary gland, increased ovarian activity or adjustments in other hormone levels within the brain-pituitary system.

Significance and Future Directions

• This study provides valuable insights into how artificial lighting could be used to manipulate the breeding cycles in horses, which could have profound implications for horse breeders and the equine industry.
• Further research is needed to fully understand the underlying mechanisms that enable the faster transition to the breeding state under extended photoperiods, as well as to assess any potential long-term effects or risks associated with the use of artificial lighting on horse health and wellbeing.