Exercise May Affect Embryo Quality and Recovery Rate in Mares

Does exercise have a detrimental effect on reproduction in mares? And if so, are there certain times in the reproductive cycle or intensities of exercise that are more damaging than others?

Many horse owners continue to ride pregnant mares throughout the gestation period, and it’s not unheard of for someone to buy a mare, keep her in some sort of regular training or exercise program, and then be surprised by the unexpected birth of a completely healthy foal some months later. Finally, there are some reports of racing mares that actually improved in performance after they had been bred and confirmed in foal.

A recent study conducted by researchers at Clemson University and the University of Florida looked at the impact of work on mare reproductive health.

In the study, mares were divided into three groups that performed no exercise (control), partial exercise, or full exercise. Mares in the partial exercise group performed moderate exercise for 30 minutes a day during the time around ovulation and then were rested for seven days after ovulation. Mares in the full exercise group were exercised for 30 minutes a day with no rest days after ovulation. Mares in both exercise groups were found to have greater concentrations of cortisol, a hormone that can affect reproduction.

Embryo recovery rates were lower in exercised horses compared to the control group. There was no significant difference in embryo recovery rates for the partial exercise and full exercise groups. The partial exercise group had the lowest embryo quality score. This result suggests that exercise around and just after the time of ovulation might be detrimental to the well-being of ova and early embryos.

A possible explanation is that altered hormone concentrations could have an effect on the mare’s ooctyes, making them less able to be fertilized and altering normal development of the early embryo. This finding could have implications for natural pregnancies and mares used for embryo transfer. Further research may clarify these findings and their importance.