Influence of ovaries and photoperiod on reproductive function in the mare.

This research article examines how light exposure and the presence of ovaries affect reproductive behavior in mares. The study finds that a longer photoperiod can advance the start of the ovulation period, and also explores the role of ovaries in regulating hormone changes and fertility cycles.

Photoperiod and Ovulatory Season

In this study, the researchers investigated the relationship between daily photoperiod and the start of the ovulatory season. Mares exposed to a 16-hour daily photoperiod experienced a hastened start to their ovulatory season. Key findings include:

• The changes in gonadotrophin levels and follicular activity prior to ovulation were similar in both mare groups, regardless of light exposure.
• A drop in Follicle Stimulating Hormone (FSH) levels prior to the ovulatory season anticipated a decrease in 15-25mm follicles and an increase in Luteinizing Hormone (LH), aligned with the growth of an ovulatory follicle.

Seasonal Changes in Hormone Concentrations

The researchers observed seasonal shifts in FSH and LH levels in mares without ovaries; these changes were also influenced by light exposure. Notable observations include:

• No ovarian influence on gonadotrophin concentrations was detected during the anovulatory season.
• During the ovulatory season, the ovaries enhanced LH levels during oestrus (the period of fertility) and decreased them during dioestrus (the period of sexual inactivity).
• The ovaries had a negative effect on FSH levels throughout the entire oestrous cycle.

Influence of Ovaries and Photoperiod on Ovulation Start

The research reveals that the start of the ovulatory season happens when there is a sustained increase in LH levels; this increase is driven by both seasonal factors, such as lengthening photoperiod, and ovarian influence. The observations suggest that both these factors work together in triggering the ovulatory season.