A mare’s heat cycling is natural, and she’s entitled to it. However, we don’t have to put up with a mare that’s so uncomfortable she’s moody to the point it interferes with her performance or she becomes dangerous. Usually, veterinarians suggest using Regumate.
Regumate is progesterone, the hormone that is high during pregnancy and in human PMS (whose equivalent would be midcycle for a mare, not when she is in season). Progesterone can cause depression. Regumate makes your mare stop cycling and showing “heat.” However, Regumate works against building muscle, favors water retention and can lower the efficiency of the immune system. When a mare comes off Regumate, the same problems will return in full force, if not worse, and you may want to consider using hCG or vitex agnus-castus instead.
The hormone hCG, human chorionic gonadotropin, is given by your veterinarian as a single injection. It causes follicles to ovulate within 36 hours. It is often used when breeding mares in an effort to make sure they ovulate close to the time of insemination. When repeated at two-week intervals, the rapid ovulation of smaller-than-normal ovulatory-size follicles keeps the mare from showing season. The first injection can be given as soon as the mare begins to show early signs of estrus, with subsequent injections 14 days after the first.
Because this is a human hormone, some mares may develop antibodies that eventually make it ineffective. However, most mares can be maintained on hCG injections throughout the breeding season.
There are no reproductive side effects. Normal cycles resume when the hormone is stopped. A few mares may show allergic reactions, but they respond well to treatment and can be prevented on subsequent injections by corticosteroid or Banamine administration at the same time.
Vitex agnus-castus berries have been used to treat reproductive-cycle abnormalities in people and animals. The active compounds help normalize imbalances in the reproductive hormones. Mares experiencing unusually short intervals between cycles or prolonged periods of behavioral estrus may respond well to it. Vitex will not keep your mare from cycling.
Vitex agnus-castus products are available without a prescription (Equi-Naturals, www.blueridgetexas.com/equi.natural.products.htm, 972-784-7106 and Emerald Valley Botanicals www.emeraldvalleybotanical.com, 888-638-8262). You can also purchase the seeds (www.herbalcom.com, 888-649-3931 Chaste Tree Berries) and grind them yourself. Feed one ounce per day.