How to Deal With a Mare in Heat

Three Parts:Recognizing When Your Mare Is in HeatUsing Hormone Therapy to Deal with a Mare in HeatWorking With Your Mare When She is in Heat

Normally, your mare is reasonable, responsive to your instruction, and generally pleasant to be around. When she is in heat (‘estrus’), however, your mare’s behavior can change drastically and you may wonder what’s going on with her and when she’ll settle back down. Although your mare’s hormones can cause her to act pretty strangely when she is in heat, there are some things you can do (with your veterinarian’s guidance) to help you effectively deal with your mare during this time.

Part 1
Recognizing When Your Mare Is in Heat

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    Learn about a mare’s reproductive cycle. Mares are seasonally polyestrous, meaning their reproductive cycles occur at certain times of the year.[1] Typically, a mare’s cycling season will last from April through September. During these months, each cycle will last 18 to 23 days and the mare will be in heat for about 5 of those days.[2]
    • A mare’s cycling may begin as early as March and end as late as October or November. Some mares may have a transition period before the start of the cycling season or at its end, causing them to show signs of being in heat for weeks at a time.[3]
    • The part of a mare's cycle when she is not in heat is called diestrus.[4]
    • Rarely, certain medical conditions (ovarian tumors, equine Cushing’s disease, uterine infection, poor nutrition) can cause abnormal cycling behavior.[5]
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    Keep a daily journal of your mare’s behavior. During the course of one reproductive cycle, your mare’s behavior will ebb and flow. Recording her behavior—the good, the bad, and the ugly—each day will help you estimate where she is in her cycle, especially when she is in heat. Make recorded observations specific. For example, instead of writing ‘She misbehaved,’ write the details of her bad behavior (‘didn’t follow instructions,’ ‘tried to kick’).[6]
    • Keep the diary for about a month. Remember to include your mare’s behavior around other horses, especially stallions.[7] This will help you and your veterinarian devise a strategy for managing your mare when she is in heat.
    • Make the journal a team activity. Whoever is around your mare (yourself, trainers, caretakers) should record her behavior. It may even help to make a video recording of her behavior.[8]
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    Identify which behaviors may be associated with being in heat. Mares can display a range of behaviors during their cycles. Behaviors associated with estrus include elevating the tail, ‘winking’ the vulva (vulva opens and closes), and squirting urine and mucus during a squat. A mare in heat may also decrease her overall activity level.[9]
    • Gait abnormalities can also occur when a mare is in heat.[10]
    • You may find that your mare is very distracted when she is in heat. She probably won’t follow your instructions very well when you are riding or training her.[11]
    • When she in heat, your mare may also become more irritable and easily startled, as well as very sensitive to the touch. Ovulation can be painful, making your mare more sensitive.[12]
    • Be aware that some of her bad behavior may actually be associated with her coming out of heat.[13]
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    Take your mare to your veterinarian. If your mare's behavior when she is in heat becomes dangerous to herself, other horses, or you, consider taking her to your veterinarian. He or she will evaluate your mare for reproductive soundness and determine whether reproductive abnormalities or other medical conditions are causing your mare’s dangerous behavior.[14]
    • Your veterinarian will likely take blood samples and perform rectal palpitations on your mare to accurately determine where she is in her cycle.[15]
    • It may take several veterinary visits before your veterinarian can accurately diagnose your mare and devise an effective treatment plan.[16]
    • Your mare may also need veterinary evaluation if her heat-related behaviors are affecting her ability to train and compete.
    • Bring your daily journal to your veterinary visits.

Part 2
Using Hormone Therapy to Deal with a Mare in Heat

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    Discuss hormone therapy with your veterinarian. Hormone therapy is a great way to deal with a mare in heat, particularly if her heat-related behaviors are negatively affecting her training schedule or ability to compete. Progesterone has been shown to be the most effective hormone to suppress a mare’s heat, but estradiol (a form of estrogen) and oxytocin can also be effective.[17][18] Following examination, your veterinarian will be able to recommend the ideal hormone therapy treatment plan for your mare.
    • Since these synthetic hormones mimic your mare’s naturally circulating hormones, it is unlikely that you will run into problems with competition drug rules.[19] However, you should still check the rules before starting your mare on hormone therapy.
    • If your mare's heat-related behaviors are merely annoying, and don't have a major impact on her training or competitiveness, then hormone therapy is probably not necessary.
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    Give your mare progesterone. Naturally, progesterone is highest during diestrus. The synthetic form of progesterone will keep your mare in diestrus and prevent her from entering estrus. The most common form of commercially available progesterone is Regu-Mate, a daily synthetic progestin.[20]
    • Regu-Mate comes in an oral formulation, which you can either add to your mare’s feed or administer directly into her mouth via a syringe. The oral formulation is oily and can be messy, so adding it to her feed may be a little easier.[21]
    • Regu-Mate is also injectable. However, the daily intramuscular injection could cause soreness and scar tissue development at the injection site.[22]
    • With the injectable formulation, it will take about 24 hours to see an effect.[23] Heat is usually suppressed within 3 days with the oral formulation.[24]
    • You can stop giving Regu-Mate at any point. When you stop giving it, your mare will return to heat within about 5 days.[25]
    • You must wear nonporous gloves when giving your mare Regu-mate! It can absorb into human skin and cause abnormal cycles in women, as well as infertility in both men and women.[26]
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    Add estradiol to your mare’s hormone therapy. On its own, progesterone may not be very effective in reducing your mare’s irritability or other behavioral issues when she is in heat.[27] This is because progesterone does not stop your mare’s ovarian activity, meaning that follicles can continue to develop in her ovaries. The addition of estradiol 17ß would suppress follicular activity and thus may help address the behavioral problems.[28]
    • A progesterone + estradiol hormone therapy regimen can be given in either a short- or long-acting formulation.[29] Your veterinarian will let you know which would be best for your mare.
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    Consider giving your mare oxytocin. Oxytocin is another hormone that can prevent your mare from coming into heat by keeping her in diestrus. It is an injectable formulation that should be given twice a day for 14 days after your mare has ovulated (your veterinarian can help you make that determination). Oxytocin can keep your mare in diestrus for up to 30 days. She would likely tolerate the daily injections because of the small amount of drug that you would inject.[30]
    • Oxytocin does not have many side effects and may actually be less expensive than other hormone therapy options.[31]
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    Explore non-hormone therapy options. There are some other therapeutic options for dealing with a mare in heat. For example, you could give your mare herbal supplements. However, herbal supplements have not undergone rigorous scientific testing, and can have variable effectiveness. They may also violate medication rules in sporting associations, so check with these associations before giving your mare herbal supplements.[32]
    • There are a number of herbs you could consider, including chaste tree berry (hormone level regulation), European angelica (reduction of unpleasant hormone-related symptoms), red clover (estrogen-like effects), and motherwort (reduction of irritability).[33] Talk with your veterinarian before giving your mare herbal supplements.
    • Surgical removal of your mare’s ovaries (‘Oophorectomy’) is another option, but should be a last resort.[34] Although your mare will stop cycling, she may still exhibit heat-related behavior.[35]
    • Implantation of small, sterile marbles into a mare’s uterus has been shown to suppress estrus.[36] The marbles can keep a mare out of heat for up to 90 days, but this method has variable effectiveness.[37]

Part 3
Working With Your Mare When She is in Heat

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    Select easy tasks for your mare to perform when she is in heat. When your mare’s hormones are surging, it will be difficult for her to focus on tasks that she would normally be able to do quite easily. In addition, she will not want to be as active when she is in heat. For these reasons, you may need to adjust your mare’s work schedule when she in heat.
    • Pick exercises that can help her focus, such as jumping combinations or changes in gait or direction. Give her something that she already knows how to do, since she probably won’t be able to learn anything new while she is in heat.[38]
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    Do not approach your mare from behind. With your mare being extra sensitive to touch while she is in heat, especially near her hind end, avoid approaching her from where she cannot see you.[39] If your mare has a winking vulva when she is in heat, the constant opening and closing of her vulva could lead to an uncomfortable condition called pneumovagina (air enters the vagina). Pneumovagina can make your mare very irritable, so it would be best to stay away from her back end as much as you can.[40]
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    Groom your mare from front to back. Depending on your method for grooming your mare, you may need to readjust it while she is in heat. If you do not do so already, begin grooming her at her neck and shoulders, where she will probably not be too sensitive to your touch. Slowly and carefully, work your way back to her flank.[41]
    • Pay close attention to your mare’s body language when grooming her. If she is growing increasingly agitated, especially as you work your way back on her body, stop your grooming session.


  • Your goal should be to keep your mare healthy, safe, and productive when she is in heat.[42]
  • No matter how difficult your mare may become when she is in heat, rest assured that she will not be cycling all year, and there are ways to successfully manage her behavior.
  • Some mares have major behavioral changes during estrus, and some may not change much at all. Most mares fall somewhere in the middle.[43]
  • Chiropractic measures may also be effective in dealing with a mare that is in heat.[44]
  • If your mare seems to be in a lot of pain, your veterinarian may prescribe a pain medication called Banamine.[45]


  • Do not administer Regu-Mate if you are pregnant.[46]
  • Do not give your mare progesterone if she has a uterine infection or her uterine is inflamed. Progesterone could worsen the infection or inflammation.[47]
  • When you take your mare off Regu-Mate, she may experience long-term cycling abnormalities.[48]
  • Ovariectomies are expensive and not without risk.[49]

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Categories: Horse Breeding