Mare Madness



Mare Madness

I hear it all the time: "My mare is impossible whenever she is in heat, and, in fact, she's in heat most of the time!" or "Every time I want to do something with my mare, she's in heat; in fact, she was in heat for every single show last year!" or "My mare has a split personality--most of the time she's a witch. Every couple weeks she's in season, and for those few days, she is the sweetest little angel," or "My mare gets PMS," or "Sometimes this mare just won't run her best, sometimes she'll pull up or stop. I think it's when she's in heat."

Temperament and performance problems believed to be related to the estrous cycle in mares are among the most common complaints of owners and riders of mares. The problems come in a few varieties. Careful evaluation sometimes can identify the cause and lead to resolution, or at least a strategy for satisfactory management.

Rarely is the problem as simple as poor performance during estrus or prolonged estrus that interferes with top performance. For a small percentage of cases, the problem might be related to the reproductive cycle, but with the diestrous phase rather than the estrous phase of the cycle. In some of these, it turns out that the mare's best behavior might be during estrus and the problem behavior associated with the diestrous phase of the cycle. In another small percentage of cases, the mare is found to have a reproductive pathology. The most common pathology is a hormone-producing tumor that can cause various forms of abnormal behavior. Most often, it turns out that the problem is not estrous behavior, and the root cause is not associated with estrus or the reproductive cycle of the mare.

What Is Her Problem?

The first step in figuring out what is going on is to take a very close look at the problem behavior and to evaluate a possible relationship with the reproductive tract or ovarian cycle and the associated behavior. This will require the involvement of all of the people working daily with the mare, along with the help of your veterinarian. Depending on your veterinarian's specialty, he or she might consult colleagues with expertise in reproduction, behavior, or performance and training. Depending on the root cause, in some cases it might take considerable effort to reach a definitive diagnosis upon which to base effective therapy or management. It's best if everyone involved can approach the evaluation as a positive challenge, holding reasonable expectations for a useful outcome.

A good place to start is for each person involved with the mare's care or training to keep a daily diary of the mare's behavior, both desirable and undesirable. Be as specific as possible. Rather than recording summary comments, such as "great attitude today" or "a real pain in the butt today," list very specific behaviors such as "moved forward when asked," or "spooked at the fly zapper," or "flinched and fell down when girth tightened."

Watch and record the mare's behavior in her stall and with other horses. If there is a stallion or vigorous gelding available, it is also good to tease the mare daily or every other day and to record very specifically her response to the stallion. The veterinarian can follow the mare's ovarian cycle with palpation and/or blood samples for hormone determination. After at least one full month, it is good to sit down with your veterinarian and the daily diaries to evaluate a pattern (if any) that might be related to the reproductive cycle.

What might be found is that the problem behavior might or might not be associated with estrus. The chart shown on page 66 summarizes specific signs associated with estrus, diestrus, and other conditions commonly confused with estrus in mares. For example, some mares exhibit a submissive cowering sequence that easily can be mistaken as estrous behavior.

Submissive Behavior

The submissive behavior involves leaning away from a perceived threat. These mares typically go to the back corner of the stall when you enter or when another horse passes. If the mare is cornered, she might swish and wring her tail and squirt urine. This behavior sequence in the mare is analogous to the leaning away, clamping of the tail, and urination typical of a puppy or of a severely submissive adult dog. In mares, it often is the combination of the leaning, the tail action, and the urine squirting that remind people of estrus. On racetracks, this cowering behavior in fillies is sometimes called "starting gate estrous." But, of course, it's not really estrus.

How can you tell whether your mare's behavior represents estrus or this submissive behavior? True estrus in the mare involves leaning toward the stallion; submissive cowering involves leaning away from the stallion or any threat. The tail action of estrus involves a relaxed movement and lifting of the tail; the cowering sequence involves a wringing and active swishing of the tail. In the estrous sequence, the mare approaches the stallion. She will linger and eventually "break down" into a wide, squatting stance. She might flex a foreleg and turn her head back to gaze at the stallion. Her posture seems to tell the stallion she is not going anywhere and will not resist. The submissive mare looks like she's trying to escape, and if she is cornered, might fall down or run over the stallion.

In the estrous sequence, the urination is either full stream, or as the supply is depleted, might be just small spurts. Another distinguishing aspect is that submissive cowering and urination can be elicited by any threatening situation, while estrous posture and urination usually are more pronounced in response to a stallion.

We always like to evaluate these mares with a stallion, as well as in a variety of situations in which the mare interacts with people and other horses.

If the problem turns out to be submissive cowering behavior, and the mare's general physical and reproductive examinations reveal no other problems, then the most efficient approach to relieving cowering behavior in a mare involves good old horsemanship. The goal is to systematically re-acclimate the mare to the work and associated environment. Some trainers find it useful to give the mare a break for a few months with gentle handling before gradual re-entry into a full training program. For mares in race training, long-acting tranquilizing regimens have been judged as useful, with the reported positive effect of a general mellowing of the mare.

Urogenital Discomfort

Another cluster of behaviors that easily can be mistaken for estrus are caused by urogenital discomfort. Frequent tail lifting, urination, and/or straining as if to urinate can be caused by any type of perineal or vaginal irritation or discomfort. Vaginitis, bladder infections, bladder stones, urethral lesions--just about anything irritating could be making the mare act in an unacceptable or "grouchy" way.

In racing fillies and mares, air aspirated into the vagina (pneumovagina) can be irritating enough to affect training and race performance. With these mares, it is common for the behavior to intensify with work. To add to the potential confusion, the behaviors of urogenital discomfort can intensify with any sort of disturbance or social challenge, such as being pushed to work a bit harder, or in social interaction with other horses, particularly teasing by a stallion. It stands to reason that if a stallion approaches, a mare suffering vaginal irritation might show intense signs of discomfort, even if she is not in estrus.

How can you tell the difference?

One common telltale sign that tail lifting and frequent urination or straining might be discomfort rather than estrus is that the cluster might include kicking at the abdomen and other mild colic-like signs. It is rare for a mare in estrus to kick at her abdomen.

Just this month, a popular equine reproduction list server had some related discussion. The initial posting was entitled "Psychotic mare." The mare was described as having developed a pattern of showing "estrus-like" behavior most of the time. Her race trainer was frustrated with her unwillingness to work whenever she was around other animals. The mare's symptoms seemed to be more intense every 20 to 21 days. Hormone treatments given to control her estrous cycle had failed to improve the situation.

The specific behaviors listed included some behavior that looked similar to estrus, but most that suggested discomfort. Some key behaviors mentioned that pointed away from estrus and toward discomfort were "kicking and squealing." Katrin Hinrichs, DVM, PhD, formerly of Pennsylvania's and Tufts' veterinary schools and now at Texas A&M, has over the years followed a number of such cases. In evaluating these mares, the first things she looks for are possible vaginal, bladder, or urinary tract problems that could be causing irritation to the mare, especially during work.

For example, young, thin Standardbreds in training might aspirate air into the vagina, which can be quite irritating. This irritation can cause the mare to pull up or stop during training. Sometimes extreme irritation of the vagina is manifested by squatting, tail switching, and frequent urination. Hinrichs also has seen mares with similar behavioral signs turn out to have bladder atony, urethral tumors, or bladder stones.

A similarly memorable case was a mare which the rider described as showing frequent estrus. In her stall or under saddle, she frequently would lift her tail and urinate or strain as if trying to urinate. She walked with a stiff back and wide, tentative hind gate. Initial examinations indicated that the mare had a normal reproductive tract and estrous cycle.

Her actual estrous behavior was quite normal and reasonably distinct from this other behavior, although this behavior seemed worse when the mare was truly in estrus.

Some careful detective work revealed that this mare had a sliver of a tree branch deep in her vagina, with resulting inflammation and infection. As expected, the behavior problem resolved once the discomfort was eliminated.

These cases and many others like them raise an important question: If the root problem is not estrus, but rather discomfort, then why does it seem to get worse on a regular cycle that in some cases would correspond to the length of a mare's estrous cycle?

The extreme example is the occasional case in which an owner complains that a mare is lame only when she is in estrus. When in diestrus she seems sound. One possible explanation comes from a growing body of scientific evidence indicating that changes in estrogen and progesterone predominance across the ovarian cycle can affect physical condition.

For example, under the influence of estrogen predominance during estrus, supportive muscles relax compared to during diestrus, when progesterone predominates and effects good supportive muscle tone. A minor lameness might be more apparent (as well as truly more uncomfortable) during estrus compared to during diestrus. Also, evidence from work in other species indicates that the ability to tolerate discomfort varies with the cyclical changes in hormone levels.

Stallion-Like Behavior

Another class of behavior that sometimes is mistaken as estrus is stallion-like behavior. If a mare offensively attacks male horses, tends to bite and strike, herds other mares, investigates voided urine and feces, or teases and mounts other mares, then she is showing male-type behavior. This almost always means that the mare has been exposed to abnormally high levels of steroid hormones, either from a steroid-producing tumor or from a supplement or medication. Especially in its subtle form, stallion-like behavior commonly is mistaken for estrus.

Blood tests and a reproductive examination by a veterinarian can investigate the presence of a steroid-producing tumor. If none can be found, further investigative work will be required to identify a possible source of hormones. The next-most common source is performance-enhancing supplements and steroid medications. Once the exposure to hormones is eliminated, it can take anywhere from a few days to many months for the stallion-like behavior to subside.

Over the years, we have known cases in which any undesirable behavior was interpreted as estrus. The typical history was that the mare was bad every time she was in estrus. When asked how it was established that the mare was in fact in estrus, the answer went something like: "We know for sure when she's in estrus, because she is bad."

The specific bad behavior might be kicking, refusing to jump, squealing, lying down, throwing her head, running home, stomping in the trailer, biting, or any number of misbehaviors. While this might seem a bit naive, unless you are working on a broodmare farm where your future depends on accurate estrus detection, it's unlikely that you have been given thorough instruction on the fine details of estrous behavior.

If a mare is teased daily or every other day with a stallion through one or more estrous cycles, her cyclical behavior reflecting "true" estrus and diestrus, distinct from behavior of submission, discomfort, simple poor performance, or misbehavior, usually can be appreciated. The relaxed clitoral "wink," tail raised up and off to one side, and full urination and breeding posture are elements usually unique to estrus. In order for a submissive or painful mare to show full estrus to a stallion, it might be necessary to tease her in a very non-threatening manner. Otherwise, her estrous behavior will be interspersed with or masked by the submissive or discomfort behavior. If the mare is placed at liberty in a pasture next to a stallion, she can approach and interact on her own time and terms.

Variable Performance

A relatively common problem behavior reported by trainers and riders of mares is variable performance or trainability that is suspected or believed to be related to the estrous cycle. The most common interpretation is that the mare becomes less cooperative or attentive to the performance tasks during estrus. During work, the mare actually might be distracted by or show estrus to stallions, geldings, or even other mares. Careful clinical evaluation like that described above has confirmed that some mares do show periods of deterioration of performance or temperament--mild or marked--associated with a particular stage of the ovarian cycle. Similarly, some mares simply are generally hyperexcitable and difficult to handle at certain stages of the cycle. Some mares appear particularly sensitive to weight or manipulation that might affect the area of the ovaries during the periovulatory period of the cycle.

So, yes, there are some problems that truly are estrous cycle-related performance problems. These too come in different varieties.

A Good Thing, Just Too Intense

Sometimes a mare's estrus is normal, just very intense. She normally is seasonal, with estrous cycles occurring in spring and summer. In the spring, she has the normal, prolonged, and variable periods of estrus before her first ovulation of the year. After that, she has a normal, regular cycle with a period of estrus starting about every 21 days and lasting the normal few days. Then she's out of heat (diestrus) for about two weeks.

When she's in estrus, the normal behaviors of estrus are present--they are just very intense. The mare might show not just to stallions or geldings, but to other mares, to people, to the cows next door, or to the Saint Bernard in the minivan. Her stall, her legs, and her tail are wet and smelly for several days. Even under saddle, the mare might just stop, lift her tail, and urinate every time you try to pass a competitor. She might try to sidle up to the gelding next to her in the line-up.

Sometimes because the behavior is such a pain, we tend to overestimate its frequency and duration. A simple diary of the mare's behavior will reveal that it is normal estrus.

For unknown reasons, mares vary considerably in the intensity of estrus they exhibit. For example, some mares only show estrus when actively teased by a stallion. Others break down the fences trying to get to a stallion. Under pasture breeding or wild conditions, some mares pester the stallion to breed every few minutes.

Most mares can be controlled under show or performance conditions, but extreme cases will show estrus even under saddle, even with the best and strongest of trainers trying to encourage them to go on. For those mares, it might be useful to suppress ovulation or to manipulate the ovarian cycle so that the mare physiologically is not in estrus for certain events, or for an entire season.

Veterinarians will start with a basic reproductive examination to rule out any other possible complications and to establish where the mare is in her cycle. Then, considering the mare's schedule of work, a plan can be established for hormone treatments to manipulate the ovarian cycle, with the goal of either preventing estrus, reducing the duration of estrus, or timing estrus to correspond with a no-work window.


Depending on the specific problem, there are a number of treatment and management options that can be tried. Progesterone treatment at certain dose levels will suppress ovarian cycling, leaving the mare with low levels of estrogen and high levels of progesterone. Either progesterone in oil or any of several synthetic progestin preparations can be tried. There seems to be considerable individual mare variation in the behavioral response to different products and doses. Many mares appear to have a positive response to progesterone therapy even at levels that do not suppress the ovarian cycle.

Hormone implants developed for use in the cattle industry have been used regionally in horses over the past few years, as has long-acting injectable progesterone. Current research indicates that at the usual doses, these treatments do not suppress ovarian function and estrus in response to teasing by a stallion. Nonetheless, riders and trainers often report improvement of the mare's performance behavior during treatment and judge them useful in eliminating problems.


A commonly asked question is whether a mare with cycle-related behavior problems might improve if she were pregnant--a natural state of high progesterone. Again, there is no reported research on this question, only anecdotes suggesting that many mares which have had these types of behavior problems seem to "mellow out" to a reasonably good and consistent performance during pregnancy.


If there are behavior problems that seem to be associated with the ovarian cycle of a mare which you don't plan to breed, then why not remove the ovaries? The first question to ask when considering spaying is, "How is this mare during the winter?" For most mares, the ovaries stop functioning (become anestrus) during the winter. So hormonally, an anestrous mare is in a state similar to having been spayed. She will have low estrogen and low progesterone. Of course, many other training and environmental factors that affect behavior and obviously vary systematically with seasons can confound your interpretations.

Another unusual phenomenon in the mare should be understood clearly as you consider spaying a mare in an attempt to affect behavior. In most species other than horses, low progesterone and high estrogen are required to induce estrous behavior in the female. In those species, removal of the ovaries removes estrogen, and there is no estrous behavior. In the mare, however, all that is needed for display of estrous behavior is low progesterone. The addition of estrogen usually intensifies estrus, but it is not always needed.

Therefore, the spayed mare which has no progesterone typically can show estrus, at least at a low level, at any time. So if the mare's performance problems truly have been associated with estrus, spaying might make matters worse. If the mare's problem behavior was associated with diestrus and she was much better during estrus, then spaying could help. If the mare's behavior was better when the ovaries were inactive during winter, then this mare would more likely be a good candidate for ovariectomy (spaying).

Other Remedies

Open any horse magazine or supply catalog and you are likely to see advertisements for various therapies for the difficult mare. Again, depending on the nature of the behavior problem and the underlying causes, herbal formulations, massage therapy, acupuncture, and other therapies could be helpful. As we learn more about the basis of these therapies, many might become useful for management of some cases.

Behavior Modification

Whether or not an equine behavior problem is found to have a physical basis, systematic behavior modification often is useful in returning the mare to full performance. For example, a mare which has had a sore back might have secondary psychological complications. Even after her back has been treated and no longer seems painful, she might associate saddling or work with the memory of discomfort. Any behavior modification or schooling program based on improving handler-animal communication, trust, and mutually positive interaction is likely to be useful in returning such mares to full performance.

In conclusion, what could be perceived initially as an estrous cycle-related performance problem in a mare might turn out to be simple or complex. It could be related to the estrous cycle, or it might be completely unrelated. Quite often there is a physical cause that can and should be addressed. The earlier an expert veterinary team can systematically evaluate and diagnose the problem, the more likely the problem will be resolved.