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
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.
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
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
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
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.
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
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
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
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
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.
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
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.
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
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
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
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
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
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).
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.
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
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.