Q: Can you supply me with a veterinary explanation on whether a mare that is in foal can come back into season? We have had many discussions about this subject at my barn and are still divided on the answer.

Trialee

A: Mares in late pregnancy will occasionally show signs of heat, such as elevation of the tail, frequent urination, and “winking” of the lips of the vulva. They will stand stretched out, as if receptive to being bred. It is likely that these signs are the result of hormones produced by the developing gonads of the fetus that is being carried. Mares are more likely to show this behavior when they are in groups.

While these are behavioral signs of heat, there are no accompanying changes in the ovaries or relaxation of the cervix. So by a strict definition, they are not truly in estrus.