Mean Girls? - Moody Mares

“Witchy” behavior in mares is almost always blamed on their heat cycles, but the fault can lie somewhere else.

by Breanne Hill

ImageSugar and spice and everything mean. That is what some mares seem to be made of when they are in heat.

As is the case with any animal, horses can be affected by the hormonal changes that occur during the heat—or estrus—stage of the reproductive cycle. This phase, in which a mare is most receptive to breeding, commonly manifests itself through such behaviorisms as tail swishing and squealing when around other horses, and can be accompanied by a short attention span and a bad attitude.

In practically every equine discipline, there are trainers and owners who dislike working with female horses for this reason. They simply don’t want to put up with the monthly hassle that is created by a mare that is in heat.

To assume that estrus is the only reason a mare gets moody, however, is a mistake. Veterinarians recognize that a horse that seems mentally imbalanced may be going through more than just the usual hormonal changes. She could be experiencing any number of health problems that have her behaving in a less-than-nice way.

Shaylyn Bliss, DVM, an equine reproductive specialist at Performance Equine Associates in Whitesboro, Texas, cares for hundreds of mares every breeding season. She says the key to determining whether your mare is being affected by a standard estrus cycle or is suffering from another medical condition is to know what is “normal” behavior for her.

Finding “Normal”
Bliss is often asked to assist the owners and trainers who have complaints about a mare’s conduct. These visits, she admits, can be somewhat predictable.

"They're usually having extreme problems with training or they’ve noticed a decline in performance,” says Bliss. “Or the mare is being uncooperative and fractious and sometimes even aggressive.”

According to Bliss, these clients have almost always diagnosed the horse themselves at home. And the gist of this diagnosis is usually that the mare's problems are all related to her heat cycle.

"I've had several clients bring their mares in, and they claim a lot of things and try to associate that with the mare being in estrus," says Bliss. "One of the things I hear most often is, 'Her ovaries are sore and that's preventing her from performing well.'"

In her experience, Bliss has found that these home diagnoses are often incorrect.

"I lot of times we'll check the mare and she's not even in heat," says Bliss. "So I think for some reason people tend to want to blame the mare's estrus cycle for everything that’s wrong. And I would say, most of the time, the mare's problem has nothing to do with her estrus cycle."

To avoid making this primary misdiagnosis, an owner should first be familiar with how his or her mare behaves on an every-day basis. Is she usually aggressive or submissive toward other horses—or toward people? Traditionally, has there been a difference in how she behaves when she’s in heat and when she isn’t? And, of course, do you really know when your mare is in heat?

If you admitted “no” to the last question, then it is there that you should begin tracking down a diagnosis for your horse.

A mare's reproductive cycle is relatively simple to pinpoint—if you're willing to observe and mark the days off of a calendar. As a general rule, most mares only ovulate between March and October. During the winter, without artificial manipulation, such as special barn lighting, a mare’s reproductive organs go into “hibernation” and she will not be interested in breeding.

Throughout the spring and summer, however, a mare may ovulate every 21 days. Ovulation is prime breeding time, the window of the reproductive cycle when a mare is most likely to conceive. Estrus lasts approximately three to seven days prior to the onset of ovulation, and it is the point of the reproductive cycle when a mare is most likely to shows signs of being in heat.

Why is this? In female equines, heat-related behavior is prompted by low levels of the hormone progesterone. Progesterone levels are at their lowest right before ovulation.

The intensity of the resulting behavioral changes varies from mare to mare, but Bliss says it is perfectly normal for even the most reliable horses to act differently during this period.

“(Mares) are probably going to be a little more irritable than usual during estrus,” she says. “They’ll show all the standard signs of posturing—tale lifting, squealing, backing up to other horses—and they'll urinate frequently. I would consider this all to be normal behavior. 

“They’ll just be a little bit crabby, as you would expect them to be.”

Estrus-Related Problems

It is only when a mare seems to display extreme behaviors during estrus, such as violent mood swings, listlessness or signs of unusual physical discomfort that owners need to start worrying. There are a few factors that can cause mares to have intense estrus-related pain. These difficulties are all rare, but they do exist.

For example, some mares—especially mares that have never been pregnant—may show signs of colic during estrus. According to Bliss, this can be directly related to ovulation.

"I have seen maiden mares that it seems to be painful for them to ovulate," says Bliss. "They'll be colicky, which means they are either kicking at their stomach, not eating, trying to lay down and roll. And sometimes they can be pretty dramatic about it. They'll throw themselves down and it just seems as if they are in extraordinary pain."

Bliss says that if a mare is brought to her in this state, the horse is first palpated to diagnose potential colic. Often, however, palpation shows that the mare is instead in the advanced stages of ovulation.

"Through palpating them, we can feel that their ovaries are very soft and close to ovulation," explains Bliss. "So we ultrasound them and, sure enough, they've got a big follicle there, and we'll find that after they ovulate, they recover from their colic symptoms."

Horses who are showing signs of colic should never be ignored, but if your mare displays this behavior every month during her estrus, then it is likely that she is experiencing painful ovulation.

"I've seen a few mares that do it repeatedly," says Bliss. "They predictably colic once a month and that's almost always what it is.

"There again, this is extreme. We see maybe one or two mares every year that have something like that going on. It is not the norm by any means."

Also not the norm is when the usual behaviors associated with estrus are extremely intense. This especially can be a problem in horses that travel to compete, for they may not only show an interest in stallions, but in anything that has a pulse. For this reason, many riders find their horses "uncontrollable" and “unfocused” during intense heat cycles, and this all results in a decline in performance. Owners may also find that the mare's living space, tail and legs smell bad and are wet for days on end—in all not a pleasant situation when a horse is expected to perform.

Additionally, in atypical cases, mares can become violent and unpredictable during an intense heat cycle. Sometimes referred to as "heat rage," this behavioral problem is perhaps the most dangerous result of estrus, and the one that owners fear most.

The reasons why some mares have more intense cycles than others are for the most part undefined. However, as a general rule, tests have found that a majority of mares are highly sensitive to the weight of riders or to any piece of tack that comes in contact with their stomach and flank during estrus.

There have also been recent studies that suggest that, because horses experience high levels of estrogen during estrus, their muscles can relax, affecting performance and even sometimes causing the mare to show signs of lameness.

All of these problems can be justifiably blamed on estrus.

Non-Estrus Problems

There are more non-estrus related medical conditions blamed on the heat cycle than there are those that are actually estrus related.

One of the most common of these non-estrus conditions is a cancer known as a granulosa tumor. This type of tumor can easily disguise itself as estrus-related as it is an affliction of the ovaries. A mare that has a granulosa tumor may exhibit all the signs of an intense heat cycle. Overly aggressive behavior toward other horses and people, as well as indications that the horse is in severe pain can be symptoms of this type of tumor.

"These tumors secrete an excess amount of hormones," explains Bliss. "Thus, you might see your mare displaying 'stallion-like' behavior.

"The good news is these tumors are fairly easy to diagnose."

Diagnosis of a granulose tumor begins with an ultrasound. If the mare has a tumor, the ultrasound will show the sick ovary to be enlargened with many, multi-colored folicles around it. These folicles are multi-colored due to the fact that they are holding an excess amount of fluid.

The non-afflicted ovary in this scenario will be tiny. This is because the cancerous ovaries secrete hormones that cause the other ovaries to become inactive.

"This happens to maybe one mare in a couple of hundred," says Bliss. "It's not something you see every day, but out here we see one or two every breeding season."

Other medical conditions that may easily be mistaken for estrus are urinary tract, vaginal or bladder infections. All of these problems can cause a mare discomfort and may prompt her to show signs of being in heat, such as posturing and frequent urination.

"In mares, urinary tract and bladder infections are extremely, extremely rare," stresses Bliss. "If they have one, there is probably some other injury or medical problem that caused it. In other words, the infection will not be the primary problem."

In the end, however, these health-related issues are less common than their human-caused counterparts. Bliss reports that the most prominent cause of mares showing estrus-related symptoms when they are not in estrus is the care they receive at home. Sound strange? It might not when you consider that 95 percent of a horse's physical and mental health is reliant upon the choices of her caretaker.

For instance, there are some performance-enhancing supplements that can cause mares to have "rage" and exhibit stallion-like behavior. Steroids and even some types of medications have been linked to aggressiveness in mares. Remember, as it is with humans, different horses will have different reactions to foreign substances in their bodies.

Horses can also have aversions to training methods and workout regimes. Bliss says that she sometimes finds herself having to give trainers and owners "the bad news" that their mares' problems have nothing to do with estrus and everything to do with the conditions at home.

"A lot of times, an owner or trainer has an interpretation of what is going on," says Bliss. "They'll say things like, 'My mare is in heat all the time.' Well, that's a good indication that her problems have nothing to do with estrus because mares are simply not in heat all the time.

"Veterinarians are often faced with having to tell people that their mare is not having a medical issue, but a training issue. That's a pretty frequent occurrence, actually."

Bliss claims that this scenario is especially true with equine athletes that have a strict, demanding training regime.

"Look, horses get sore backs,” she says. “They can have sore tendons and joints. They can be experiencing pain or exhaustion or boredom from their training situation. All of this can cause a bad mood and make a horse uncooperative in a competitive situation."

Young mares are especially vulnerable to this type of training-related pressure. And barrel horses are no exception.


The treatments open to owners whose mares are experiencing behavioral problems—both estrus and non-estrus related—vary greatly.

For estrus-related problems, some owners have turned to supplements that contain progesterone. In higher recommended doses, progesterone can actually prevent a mare from ovulating and, therefore, suppress the effects of estrus. Again, individual mares will react differently to this treatment.

Other more controversial methods of estrus suppression include “the marble method” and having the horse spayed.

The marble method requires a 35 mm sterilized glass marble to be placed in the mare’s uterus approximately 24 hours after her last ovulation. If left in, the marble has been found to keep a mare from entering estrus for months at a time. Of course, owners report varying degrees of success with this method, with some claiming their mares’ attitudes completely changed for the better and others stating that the method had no effect whatsoever on their mares’ behavior.

It seems that if nothing else works, and the situation is critical, spaying is the last hope of some mare owners.

A mare that becomes dangerous or problematic only when she is in confirmed heat may benefit from being spayed. However, there have been cases when mares continue to show signs of estrus even after being spayed. The reactions to this method seem to vary from individual horse to individual horse.

Probably the most natural method of attempting to calm a moody mare is to let her have a foal. During pregnancy, mares experience high levels of progesterone and, according to old cowboy logic, giving birth and caring for a foal can make a mare mellow. But, as is the case with other “home remedies”, such as herbal supplements, acupuncture and message, there is no official scientific conclusion from the world of veterinary medicine on this method, only the word of horsemen and those who practice in these fields.

Meanwhile, non-estrus estrus related problems can be just as invasive to treat.

In the case of granulosa tumors, the affected ovary must be removed.

“Once that ovary is removed, then in a few weeks the mare’s behavior seems to return to normal,” says Bliss. “And most times, they will reproductively be fine. The other ovary will rebound and be able to ovulate.”

Horses also can generally rebound from any supplement or training related behavioral problems—if the situation is remedied. Removal from problem causing supplements may be required and choosing a different training path or event schedule may need to be considered for a positive change to take place.

So, does this mean most mares are really the mean girls they are made out to be?

The answer depends on the mare. An owner may evaluate a horse and find that she truly does just have a difficult attitude—all the time. Or he or she may find that the mare is suffering from a medical condition that is beyond the horse’s control.

What is certain is that jumping to conclusions about a mare being in heat isn’t likely to benefit either party.

Neither is avoidance of using a mare as a riding partner because of the “witchy mare” myth.

Mares can be exceptional performers and worth the minor trouble that a normal estrus cycle causes. One only need look at the careers of current barrel racing hotshots, such as Talents Dark Angel, Mulberry Canyon Moon and Sugar Moon Express, to see that this is true.

Breanne Hill is managing editor of Barrel Horse News. E-mail comments on this article to This email address is being protected from spambots. You need JavaScript enabled to view it..