Seasonal changes in ovarian activity: lessons learnt from the horse.

The research article focuses on the annual reproductive cycle in horses, specifically how changes in daylight duration affect ovarian activity, and its implications for breeding horses earlier in the year. The study also explores the various factors (endocrine stimuli, local growth factors) that influence this process.

Understanding the Effects of Daylight on the Equine Reproductive Cycle

• The research emphasizes on how short days or reduced daylight during winter play a critical role in the annual reproductive cycle of horses. This comes into play as a reduction in ovarian activity which results in the absence of ovulation.
• This phenomenon has implications for the equine industry, particularly for breeders who wish to breed mares early in the year. With the lack of ovulatory activity in winter, this becomes a significant challenge.

Role of the Hypothalamus-Pituitary Axis

• The anovulatory season in horses is the result of a decrease in the secretion of pituitary gonadotropin, the hormones that regulate the functions of the ovaries. This reduction is triggered by the inhibitory effects of short photoperiod or reduced daylight on the hypothalamus-pituitary axis, a system that plays a key role in many functions of the body, including reproduction.

Response of the Ovaries to Various Stimuli

• Studies show that ovarian responses to endocrine stimuli during the anovulatory season are influenced not only by the circulating concentrations of trophic hormones but also by locally produced growth factors. These factors are proposed to be modifiers of follicular responses to gonadotropins, hormones that stimulate the growth and function of the ovaries.
• Therefore, the regulation of the reproductive process during the anovulatory season of horses, particularly the ovarian dynamics, is not only systemic but can also be influenced at a local level by these growth factors.

Summary of Current Research

• The article provides a concise summary of the current knowledge on the dynamics of ovarian activity during the equine anovulatory season including the regulatory mechanisms involved both at the systemic (involving the whole body or system) and the local levels.