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