by Casie Bazay Collaborator

Debunking the Mare Heat Cycle

Debunking the Mare Heat Cycle

As far as reproductive status goes, mares typically mature somewhere between 12 and 15 months of age. This is when their “heat” cycle begins, in which the mare ovulates and is able to conceive. The actual time period when a mare comes into heat is known as estrus, and this is the specific stage in the horse’s cycle when a mare will be receptive to a stallion. 

Your Mare’s Estrous Cycle--What’s Normal?

How often does a mare go into heat?

 The average heat cycle (period from one estrus to the next) lasts 21 days, but it can vary from 19 to 26 days in some horses. Estrus typically lasts five to seven days (six being average), but could be as short as two days or as long as ten days. The period when a mare is not actively in heat is known as diestrus, and this typically lasts 2 weeks.

Each stage of a mare’s cycle is controlled by hormones produced in the pituitary gland, ovaries, and uterus, and these hormones are affected by external factors such as day length, temperature, and nutrition. Because a mare’s reproductive status is affected by the length of daylight, they experience their first heat in spring, with cycles lasting into late summer or fall. Most mares do not cycle during the winter months unless kept under lights in a barn. 

How do you know when a horse is in heat? 

A mare’s behavior often changes while she is in heat, and some signs that indicate estrus include restlessness, hyperactivity, and, in some cases, less interest in eating and sleeping. Your mare may also exhibit frequent urination, straddling posture (squatting), and clitoral “winking”. However, most mares will not show overt signs of estrus unless a stallion is present.

If your horse shows signs of being in estrus on a frequent basis, physical problems could be present, such as ovarian tumors, urinary tract or bladder infections, or even musculoskeletal pain (especially along the back). 

Foal Heat

The first heat cycle occurring after a mare foals is known as ‘foal heat’, and this happens approximately 7-14 days postpartum. In order to keep with a 12-month foaling schedule, many breeders choose to breed the mare back during this time period. Though this works well for many mares, other mares may not be physically ready for a foal heat breeding. 

How to Support Your Mare’s Reproductive Tract

Most younger mares have relatively few issues when it comes to their reproductive health, however, as she begins to age, her reproductive health may decline. Supporting your mare with proper nutrition, including high quality forage, and ensuring vitamin and mineral needs are met will help to foster good reproductive health. 

A recent study in dairy cows showed that probiotic supplementation had a positive effect on reproduction, leading to larger ovulatory follicles, shorter estrous cycles, and improved reproductive performance.1 This may very well be true in horses, as well, since we know that gut health is connected to overall health, which would include reproductive health.  

Consider supplementing with high quality probiotics for horses to support every aspect of your mare’s health. 

Further Reading:


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