I might be a little cranky at this time of the month.

Yes, even horses may act a little cranky at this time of the month.  Many horse owners will tell rookie horse shoppers “don’t buy a mare because of that issue”!  That didn’t stop me from buying a mare as my first horse.  Bailey was not “marish”, a term horse owners use to describe a cranky or unwilling mare when they come into season.  Hormonal mares are quite common, but being in season doesn’t cause a problem for all of them – much like women, some mares will barely notice their seasons passing, while others really suffer.  You can tell when your mare is in heat by these signs: she is very “friendly” with male horses; she often lifts her tail and “winks” her vulva, urinating a little bit frequently; she may seem a little moody or have a different attitude.


This will be my second year with Cheyenne going into heat this spring.  I learned a lot from her last season.  She is a horse that can have a very hard first heat of the season.  Last year she got very cranky, and very mean to Bailey and me.  I have now learned her cycle pattern and I am ready for her this year with a different attitude to help her through it.  The rest of the year she is not mean when in heat, but she is definitely not focused when there is a gelding or stallion around, especially her boyfriend “Cowboy”.  She will constantly squirt, stop working, and flirt to the male horses.  This was totally new to me as an owner of mares, since Bailey could care less about male horses when she is in heat

Horses are referred to as seasonally polyestrus. This means they have breeding season in which they have multiple heat cycles and a period where they will not go into heat. For horses the wintertime is the period without heat. Towards the end of winter in February and March they start going into heat on an irregular basis. Usually by the end of April mares will have regular heat cycles which last until about October.

The estrous cycle, also known as “season” or “heat” of a mare occurs roughly every 19–22 days and occurs from early spring into autumn. The estrous cycle during the active months is controlled by the interaction of various hormones within the body. However, it all starts with the eye, which allows the entry of light. As spring approaches, there is an increase in day length and temperature. If the mare is living off the land, there also is an increase in the quality of nutrition as new grass starts to spring up. As the mare’s brain records the increased amount of light and higher temperatures, the hypothalamus gland located within tissues of the mid-brain is stimulated.  As the days shorten, most mares enter an anestrus period during the winter and thus do not cycle in this period.

Mares do not have “periods” the way that humans do. They do have an ovulation cycle, but they do not actually bleed through their vulva. If no fertilization takes place, the uterus reabsorbs the endometrium. This breakdown of the endometrium without vaginal discharge is sometimes called covert menstruation.

Cheyenne angry head

Why do mares get a little moody when they are in season?  It is possible that the rise in oestrogen levels during ovulation causes mood disturbances, much like they do in humans. Hormonal mares can show various symptoms, very much depending on the extent of the problem, and they generally become difficult to handle and ride.  Here are some of the signs noticed:

  • Easily distracted
  • Aggressive/grumpy
  • Resenting being groomed and tacked up
  • Oversensitive about being touched
  • Squealing
  • Biting
  • Kicking
  • Unwilling to work
  • Poor performance
  • Excessive flirting
  • Low-grade colic
  • Repeated urination
  • Change in energy levels

The behavioral changes may even be caused by something as simple as the mare’s natural drive to breed while she is in season, overriding her willingness to co-operate with things like being ridden.

If your mare gets hormonal, there’s not much you can do to prevent it, but there are some things you could try to help ease the situation. Try keeping mares in a separate field away from geldings, so that your mare isn’t pestered by the geldings and she can’t flirt with them. This will also help to avoid any potential injuries caused by unwanted advances.  Some owners find that herbal supplements help – Chaste berry has been found to be effective in balancing hormones.  I have been told Camomile is useful for cramps, calming and relieving pain.  Vervain is said to relieve tension and is good for horses who are sensitive about being touched.  I actually give a heaping tablespoon of raspberry leaves daily to my mares.  I am not sure if it makes a difference, but I see no harm in it either.

Most female horses are not spayed.  Spaying a mare is a more complicated medical procedure than gelding, involving entering the abdominal cavity. Although there is more than one way to spay a mare, each resulting in the removal of the ovaries, the procedure tends to be painful and there can be scary complications, such as bleeding from the ovarian artery, which can be difficult to control. To neuter a horse is to geld it and the result is a horse called a gelding. There really isn’t a need to spay female horses since the majority of male horses are gelded, an easier procedure, so over population of unwanted horses is not an issue with owned horses.

I love owning mares, although I have never owned a gelding for a comparison.  Maybe because I am a woman I can relate to how they feel.  I try to keep that in mind when they are in heat.  I respect that my girls may not feel great some days. Being sensitive, understanding, adaptable and sympathetic in handling and training is key to get the best out of your mare, especially while she is in season.

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