How Often Do Horses Go Into Heat and When Do They Start?

September 25, 2022
how often do horses go into heat

If you own horses, especially mares, you will need to know how often they go into heat and when they start. Let’s have a closer look!

Horses (mares) usually start experiencing heat cycles when they turn one year old. The cycle generally lasts three weeks, and your mate will be in heat for anywhere from two to ten days. Their breeding cycle is usually from April to September, depending on location.

In this article, we will examine how often do horses go into heat, what the signs are, and what you need to do to regulate or manage your horse’s heat cycle. 

When Do Horses Go Into Heat?

Horses reach sexual maturity from the age of one year old. From this age, female horses (mares) start their heat cycle, which is referred to as estrus. Mares stop experiencing heat cycles at around 20 years old. Your horse’s cycling season usually lasts from April to September. It can even begin as early as March and end late in October or November.

They typically produce one or several follicles during their breeding season. Unlike mares, stallions are always ready to breed.

How Often Do Horses Go Into Heat?

A horse’s heat cycle is usually three weeks long. However, many factors influence the exact time when horses go into heat, such as age, location, and season. Because of this, the heat cycle varies from horse to horse.

It occurs in female horses between the ages of 15 and 18 months, depending on the breed. It generally lasts about two to three weeks until ovulation with a seven to 14-day luteal phase (when progesterone is released).

Mares who aren’t pregnant may experience one to four cycles per year, and pregnant mares may appear to have a cycle during pregnancy. After foaling, mares usually go into heat six to eight days postpartum. The first ovulation can take place ten days after foaling. 

Signs Your Horse Is In Heat

It’s important to know when your horse is going through heat cycles and what you can do about it, as it can be uncomfortable or dangerous for both parties. Rising levels of progesterone and estradiol bring on heat cycles in horses. These hormones are responsible for bringing on a female’s ovulation and gestation period.

The following are signs that your horse is in the heat: 

  • Restlessness
  • Increased urination
  • Swelling of the genitals 
  • A “glazed” Look in her eyes
  • Tail-raising to expose winking vulva
  • Increased interest in stallions
  • Loose bowel movements
  • Squealing
  • Lethargy
  • Easily startled 
  • Difficult to handle 
  • Gait abnormalities
  • Experiencing pain

However, an ultrasound is the only surefire way to tell if your horse is in heat. These signs and symptoms can be seen as early as two or three days before ovulation occurs, with the swelling and increased urination being noticed right away. If you notice any of these signs, it is important that you act quickly to prevent your horse from becoming overly agitated.

How Often Do Horses Go Into Heat

How To Manage Your Horse’s Heat Cycle

It cannot be easy to handle a mare in heat, but ultimately, you’d want to keep her healthy and safe through this period. The best way to deal with your horse’s heat cycle is to have her on a schedule. This will allow you to keep an eye on her to ensure she doesn’t get too worked up or hurt herself. 

If your horse is in heat and she becomes overly excited or starts thrashing around, use a lead rope or tie her up in case she hurts herself. Suppose your horse starts to urinate more than usual clean her up and give her some time to calm down. Don’t punish your horse. You can also do other things to manage your mare’s heat cycle.

Have A Stallion Ready

If you know that your horse is going through a heat cycle, make sure to have a stallion ready before the time comes for ovulation. If you don’t have one already, try to find someone who will be able to help out when needed. You may also want to prepare a place where the two can be alone, as some horses will get agitated about being around other horses or people.

If you have decided that you do not want your mare to breed, you will need to keep her separate from all your stallions to avoid pregnancy. 

Let Her Exercise To Help Her Focus

Some people say that you should put your horse on a schedule of exercise and work during her heat cycle. They claim this helps prevent restlessness and keeps things from getting out of hand. 

However, it is important to remember that your horse’s hormones are already circulating at an increased level, so working her may cause her to become more worked up than normal. Let her do easy tasks if you decide to work your mare. Choose exercises that will help her focus, such as:

  • Jumping combinations
  • Changes in gait or direction
  • Exercises that she already knows how to do

Don’t Approach Her Suddenly

When your mare is in heat, she will be sensitive to touch, especially near her hind end. So, avoid approaching her from behind where she cannot see you. This is especially true if she has a winking vulva during her heat cycle (which is the opening and closing of her vulva). 

A winking vulva can lead to pneumovagina, during which air enters the vagina, causing discomfort to your mare. 

Groom Your Horse

If your mare is in heat, you may want to adjust how you groom her. When she is in heat, groom your mare from front to back. Begin with your mare’s neck and shoulders since she will not be too sensitive to your touch in these areas. 

washing horse in heat

With slow movements, work your way to her flank. It’s important that you pay attention to your horse’s body language when you are grooming her. Stop grooming her when she seems agitated, especially when you groom the back of your mare’s body. 

Keep Her Away From Stallions If You Don’t Want Her To Breed

If you have decided that you do not want your horse to breed, you will need to keep her away from other stallions. Put her in an area that is fenced. The fence should be high enough so that a horse won’t be able to jump over it. 

Horse health in summer heat

Get Advice From An Expert

If you’re not an expert on horses, it might be wise to ask for guidance from an expert on how to manage your mare during her heat cycle and prevent pregnancy. You can also do some research online and read books to understand your mare’s cycle better. 

Use Hormone Therapy

You can visit a veterinarian to discuss hormone therapy as a way to deal with a horse in heat. This might be the perfect way to deal with it if your mare’s behavior is negatively affecting her training or competitiveness. 

The veterinarian may use progesterone, estradiol, or oxytocin to suppress the mare’s heat. However, your vet will need to examine the mare to establish the appropriate hormone treatment plan. Progesterone will keep your mare in diestrus (part of the cycle when she’s not in heat) and prevent her from going into heat. 

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Estradiol can be more effective than progesterone since the latter does not end your horse’s ovarian activity, so follicles will still develop. Estradiol suppresses follicular activity and will address your horse’s behavioral issues. Estradiol can be administered in conjunction with progesterone. 

Oxytocin also prevents your mare from going into heat. You can give it twice a day for two weeks following your mare’s ovulation. This hormone keeps your horse in diestrus for up to one month. It is an affordable option and does not have a lot of side effects. You can usually administer these hormones through an injection or orally. 

Injections may cause soreness, though, and it will take about one day for the effects of the hormone. Hormone therapy is unnecessary if the mare’s behavior is simply annoying and does not have any major impact on her training or competitiveness.

horse heat treatment

Give Your Horse Herbal Supplements

If you do not want to administer hormones to your mare, there are other options you can consider. While herbal supplements have not undergone scientific testing, many swear by their benefits and effectiveness. 

Herbs you can consider giving your mare include:

  • Chaste tree berry
  • European angelica
  • Red clover
  • Motherwort 

These herbs may assist in regulating your mare’s hormones, reducing unpleasant symptoms, and reducing irritability.

Give Your Mare Pain Medication

Some mares experience pain during their heat cycles. You can give your horse pain medication like Banamine to alleviate her pain and irritability. Be sure to consult your vet prior to giving your mare any medication. 

Consider An Oophorectomy 

Although not ideal, you can also consider removing your mare’s ovaries (oophorectomy) to stop her cycling. It’s important to remember that she might still exhibit some heat-related behavior. 

Visit A Veterinarian 

If you are unsure about anything or some of your mare’s symptoms worry you, you should take her to the vet, especially if she is a danger to you, herself, or other horses. Your vet will look for any reproductive abnormalities or medical conditions that might be causing your horse’s behavior. 


It can be difficult to know how to handle a mare in heat and what to expect, especially if you are inexperienced with horses. Hopefully, this article helps a ton! Remember, if you’re unsure about anything, it is best to talk to a vet.


I'm Bo, the owner of Smarter Horse. Helping horses be smarter by educating their people.  To find out more about me, click here

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