“My mare does not seem to come into heat. What can be done about this?”

During the breeding season, some mares may show no signs of estrus, or period of heat, particularly if they are stabled. This is not a matter to worry about, unless you intend to breed from the mare. Hormone treatments that can either suppress or initiate estrus in mares is now available. Estrus suppressants are useful if a mare is very hard to manage while in heat, but are not permitted for animals that are entered in competitions. It should also be remembered that pregnancy is a possible cause that a mare will not come on heat. It is imperative that you know whether or not the mare is pregnant before the administration of any hormone-altering medications. Any possibility that the mare could be in foal should be thoroughly checked by a veterinarian before such treatment is given; drugs used to induce estrus cause abortion if a mare is already pregnant.

“My mare seems to always be on heat or tries to mount other mares. Should I be concerned?”

Although geldings may sometimes attempt to mount mares, other mares usually do not. Mares show prolonged estrus early in the year, but if this occurs later in the season it may be a sign of a hormone problem in the ovaries. Some mares do not show estrus behavior and may also develop “stallion-like” tendencies. These tendencies include attempting to mount other mares or exhibiting a thickened neck or “crest.” These symptoms may be caused by an ovarian tumor, and a veterinarian should be contacted if any of these behaviors begin to develop.

“My mare keeps coming back into heat in spite of being covered by a stallion. Is something wrong?”

This is usually a sign that the mare has a genital infection. Mares are usually “swabbed” before they visit a stallion to make sure that no infection is present which may infect the stallion and be transmitted to other mares. However, “clean” mares may become infected at covering and require treatment afterwards. Poor confirmation of the vulva (if it is sloping, slack, or damaged at foaling) causes some mares to suck air into the vagina. This creates infection and prevents them from getting in foal. Simple stitching by a veterinarian can remedy this problem.

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