Grass greenness flush can influence breeding phenology and fertility in equatorial thoroughbred mares in the absence of photoperiod variation.

The study investigates the influence of grass greenness on the breeding patterns of thoroughbred mares in Ecuador, where there’s no significant variation in daylight hours. The data suggests that mares are more likely to become pregnant after the rise in grass greenness at the start of the year, despite breeders attempting to schedule pregnancies at two different times in the year.

Research Background

• Reproductive phenology, which refers to the timing of breeding cycles in animals, is often influenced by environmental factors. For horses, the key environmental stimulus traditionally is the variation in daylight hours.
• However, at the equator, there’s minimal variation in daylight hours year-round, meaning other factors may influence breeding patterns. In this study, the availability and greenness of grass across different seasons were examined as a potential influencing factor.

Methodology

• The researchers collected data from 929 services to mares between 2006 and 2011 on an equine farm in Ecuador, an equatorial region that experiences strong grass seasonality.
• They were not able to use actual birth data to track natural breeding rhythms because the timings of these births were influenced by human management decisions.
• Instead, they tracked shifts in the probability of pregnancy after service as a gauge of a mare’s natural breeding cycle.

Findings

• The data showed that mares tend to become pregnant more frequently following periods of green-grass availability, which peaks at the start of each year (around February).
• This occurred despite the fact that farm managers attempted to schedule pregnancies to occur in two distinct periods throughout the year, suggesting that grass availability might be a natural cue for breeding in equatorial regions.

Implications and Applications

• This research could have significant implications for managing breeding schedules on equine farms, particularly in equatorial regions. By providing green-grass stimuli during the right season, breeders may improve the success rates of their services and enhance the welfare of the animals.
• The findings reiterate the importance of considering environmental factors in managing breeding schedules, reflecting the natural selection pressures that have shaped animal reproductive patterns over time.