Pregnant Mare Exercise: No Negative Effect on Fetuses in Study

It's human nature to do everything to protect an unborn baby--even an equine baby. And humans that we are, some of us tend to think that means we should keep a broodmare's physical efforts down to a minimum. But new research is showing that even nine months into pregnancy, mares can handle moderate-level exercise with no detrimental effects to themselves or their foals.

"Moderate exercise that is performed on a limited basis is fine, as it does not appear to produce evidence of stress (in the fetus)," said study co-author Kenneth H. McKeever, PhD, FACSM, professor, equine exercise physiologist, and associate director of the Equine Science Center at Rutgers the State University of New Jersey.

Most notably, the heart rates of 9-month-old fetuses remained unchanged during and after maternal exercise. The study mares, six unfit Standardbred broodmares, were trotted on an inclined treadmill at various speeds for one-minute intervals.

The mares' heart rates did rise, but not as high as they did during the same exercise tests six months after delivery. Furthermore, plasma cortisol and plasma lactate concentrations were lower for the pregnant mares than for the same mares post-partum for the same exercise tests. These results indicate that the pregnant mares managed the exercise better and were actually less stressed during exercise than non-pregnant mares, study authors said. It also means the unborn foals are not being stressed by the exercise, either.

"If the mare's cortisol goes up and crosses the placenta and enters fetal circulation, the fetus would begin to break down lean tissue, increase its own metabolic demand, and thus increase heart rate," said Robert A. Lehnhard, PhD, associate professor at the Department of Exercise Science at the University of Maine, and primary author of the study. "But clearly that's not what's happening here."

So even if human nature tells you to pamper your pregnant mare, be reassured that moderate exercise is perfectly safe for her and her unborn foal.

The study, "Maternal and foetal heart rates during exercise in horses," was published in 2009 in Comparative Exercise Physiology. The full text is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.