Spaying Your Mare: Is It a Good Idea?

“My mare acts terrible when she’s in heat.” How often do owners of mares repeat these words? While some mares don’t have any problems when they come into heat, others show misbehaviors ranging from mild skittishness and inability to pay attention, through bucking and squealing, to dangerously violent or aggressive acts toward humans and other horses.

Physical discomfort may trigger misbehavior in fillies and mares. Some mares have quite a bit of discomfort before ovulation when large follicles develop, putting pressure on the ovary. In rare cases, ovulation causes bleeding into the ovary or abdomen. Irritation from the blood is painful, causing the horse to act sour or colicky.

Even when physical discomfort doesn’t seem to be present, hormonal changes during estrus can make mares act jumpy and unable to pay attention to the rider. Some ovarian tumors secrete testosterone, a male hormone, leading mares to develop stallion characteristics including herding other mares and fighting horses and people that approach the group.

Spaying—in equines, the surgical removal of a mare’s ovaries—sometimes puts a stop to physical problems and emotional mood swings related to estrus. However, because each horse has a different personality, spaying won’t turn every witchy mare into a pleasure mount. One way to judge whether spaying is a good idea for your mare is to observe her behavior in the late fall, winter, and very early spring when she is not cycling. If she’s well-behaved and cooperative during this period of ovarian inactivity but impossible from mid-spring through early fall, it’s likely that some of her problems are hormone-related. On the other hand, mares that bite, kick, or are generally rebellious and hard to get along with all year long probably won’t be helped by spaying. Spaying will also have no effect whatsoever on the behavior of horses that are poorly trained or handled by inexperienced or ineffective riders.

If you think your mare is a candidate for spaying, first get a veterinarian’s opinion as to whether the mare’s problems may be due to other causes such as back pain, lameness, or another condition that can be treated. Your veterinarian may suggest a course of synthetic progesterone to see whether suppressing the mare’s normal estrous cycle is followed by an improvement in temperament and behavior. If the decision to spay is made, there are several ways to perform the surgery including laparoscopic removal of the ovaries through flank incisions; intravaginal incision; or a procedure in which the ovaries are left in place but their blood supply is banded off, causing the ovaries to degenerate.

Except for the possibility of infection or bleeding, there are relatively few complications after spaying. Recovery time depends on the type of surgery but most mares can return to work after three or four weeks. Behavioral changes will probably happen somewhat more slowly, but the worst problems can be expected to abate at least partially in about 75% of spayed mares.