Effect of environmental factors and changes in the body condition score on the onset of the breeding season in mares.

The research article investigates the effects of various environmental factors and changes in body condition score on triggering the breeding season in mares. The study found that increased daylight intensity and artificial photoperiod exposure significantly advanced the first spring ovulation, while factors such as ambient temperature and body condition score had little effect.

Study Design and Methodology

• The research was designed to evaluate the role of ambient temperature, daylight intensity, and changes in body condition score (BCS) on the onset of the breeding season for mares, specifically looking at the timing of the first ovulation after winter anestrus (a period during winter when mares don’t cycle).
• 211 mares were kept in barns with different ambient temperatures and daylight exposure, but they were all exposed to the same artificial photoperiod, apart from a control group that was exposed to a natural photoperiod.

Key Findings

• The results showed that an artificial photoperiod and an increase in BCS over the winter significantly advanced the first spring ovulation. This means that mares exposed to artificial light started their breeding season earlier compared to those on a natural light cycle.
• The BCS at the start and end of the anestrus period, as well as a modest increase in the ambient temperature in the barn, had no effects on the interval to the first ovulation.
• One of the most important findings was that the intensity of light during daytime significantly advanced the first spring ovulation. Higher light intensity during the daytime led to an earlier onset of the breeding season.

Conclusions and Implications

• The study suggests that greater exposure to sunlight, especially to the blue light spectrum, advances the onset of the breeding season. This effect is likely due to the biological effect of short wavelength blue light, which impacts melatonin suppression and biological rhythms.
• The researchers propose that mares should be exposed more directly to the blue light component of daylight to improve their response to the artificial photoperiod.
• This research can help enhance the conditions that lead to an efficient spring transition of breeding mares, hence proving beneficial in optimizing breeding schedules in horses.