In humans, moderate exercise in pregnancy seems to do no harm and may help limit excessive weight gain and maintain fitness for the birth. What about horses? Many pregnant mares are ridden and subject to moderate training up to the later stages of pregnancy.
A research team from the University of Maine and the Equine Science Center, Rutgers University, New Jersey compared the response of pregnant and non-pregnant mares to a graded exercise test.
Six unfit standardbred mares were assessed when nine months pregnant and again eight months later after weaning. The exercise test was carried out on a treadmill inclined at 6%. The speed increased in steps of one minute each at 4m/s, 6m/s and 7m/s.
At each stage of the graduated exercise test, mares had lower heart rates when pregnant than after weaning. Plasma lactate concentrations rose less in response to exercise when mares were pregnant than when they were not. The researchers speculate that this might be due to greater cardiovascular efficiency during pregnancy.
Resting plasma cortisol levels were lower during pregnancy than when the mares were not pregnant.
When exercised, pregnant mares showed no increase in cortisol levels. In contrast, when they were not in-foal, the mares showed a normal increase in plasma cortisol during and after the exercise test.
Neither did exercise have an effect on foetal heart rate. This suggests that the unborn foal is not stressed by the mare undertaking moderate exercise.
The researchers conclude: “these data suggest that pregnant mares benefit from greater cardiovascular efficiency during pregnancy. They should be able to perform limited moderate exercise without any major deleterious effects on their unborn foals or themselves during late gestation.”