Effects of artificial light on the oestrous cycle of the mare.

The study explored the impact of artificial light on the reproductive cycles of mare ponies. The researchers found that exposure to simulated environmental conditions reflecting a different time of year led to significant changes in ovary function and sexual behaviour, suggesting that light can play a critical role in regulating reproductive processes in these animals.

Research Context and Methodology

• The researchers conducted a controlled experiment using 14 pony mares, which were divided into two groups.
• The experiment lasted for 120 days, from October 17 to February 15.
• All ponies were stationed in the University Biotron where factors like temperature and daily photoperiod (daylight hours) were adjusted.
• One group was kept under normal environmental conditions for that time period (control group).
• The second group was subjected to simulated photoperiod conditions typically present from March 1 to July 1 (treated group).
• The mares’ follicular growth, ovulation rate, and oestrous behaviour were observed on a daily basis. This was done via rectal palpation and by evaluating their interactions with a male horse (stallion).

Key Findings

• By day 69 of the experiment, significant differences were observed in the ovarian metrics of the treated mares compared to the control group. These include the number of follicles larger than 10mm and 20mm, the average follicle diameter, and the diameter of the largest follicle.
• Oestrous behaviour, which refers to the period when female mammals are sexually receptive to males, was recorded in all mares from the treated group. Remarkably, this behaviour was not seen in any mares from the control group. Moreover, two mares from the treated group ovulated.

Impact of Experimental Conditions Post-Removal

• After the mares were removed from the environmental control chambers, the researchers continued to monitor their reproductive activities.
• The first ovulation in the experimental and control groups occurred at an average of 147 days and 227.6 days respectively, after the initiation of the study.
• Mares from both groups synchronously followed their reproductive cycles after the first ovulation, falling into anoestrus (a period of sexual inactivity) during the subsequent winter at approximately similar times.

Conclusion

• The results of this research suggest that photoperiod manipulation, through artificial light, can influence the reproductive rhythms of mares, specifically their follicular growth and sexual behaviour.
• This has implications for understanding the reproductive biology of these animals and could potentially influence practices in animal husbandry and equine breeding.