My veterinarian said my mare probably didn't conceive this
year because she was "dirty." We treated her
and cleared up her problem, but what are our chances of
getting her pregnant, and could she get "dirty"
The term "dirty mare" can be very
complicated, and one that applies to as many as 85% of
broodmares that have problems conceiving. It consists of
more than one specific complication; in fact there are
three broad categories of problem mares.
The first group consists of mares that have an acute
infection, which means bacteria can be cultured on the
first or second day of heat. This mare is relatively easy
to diagnose--many have a purulent discharge and when her
uterus is cultured bacteria can be isolated. Once your
veterinarian determines that your mare falls into this
category, treatment consists of antibiotics to
specifically kill the bacteria that has been cultured.
The mare should be evaluated at the time the infection
is noted because she may re-infect herself if she has
poor reproductive conformation. A Caslick procedure may
be needed to stop re-infection. This involves stitching
up the vulva from the top of the vulva to the brim of the
pelvis so air and bacteria can no longer enter the
uterus, but the mare can urinate.
Treatment consists of antibiotics in the uterus for
three to four days, during which time she is not to be
bred. The mare may be bred during the next heat if there
are no signs of infection. While there are no firm or
fast rules on the treatment of this mare, the infection
should be eliminated early in the year so time remains
for her to be bred later in the season.
The prognosis for this group becoming pregnant is
good, with 60-70% of the mares conceiving after the
bacterial infection is cleared up.
The second group consists of mares that have a
long-standing, severe infection. These infections usually
are caused by bacteria such as a klebsiella, pseudamonas,
or a yeast infection. Many different treatments have been
tried, including antibiotics, uterine lavage, saline, and
DMSO. There does not seem to be a correlation between
treatment and pregnancy. At this point, if no progress is
being made, the best thing for the mare may be rest.
Clinical impressions are that a lot of mares tend to
clear up the infections on their own if they are allowed
to rest in the fall and winter and are not bred. For the
second group the prognosis is slim, with 10-25% of the
The third group usually does not culture any bacteria
from the uterus prior to breeding. The problem with these
mares is that they cannot physically clear their uteri of
the by-products of breeding. When a mare is bred, she
responds to the semen that is deposited into her uterus
by having a tremendous inflammatory response.
Reproductively healthy mares clear the inflammation
through their cervix within 24 to 48 hours. Mares that
fall into the third group do not clear the fluids for 72
to 96 hours. If the inflammation of the uterine tissue
lasts for five days, the embryo may enter a hostile
environment and possibly die.
This condition is called persistent mating-induced
endometritis or a delay in the uterine clearance. There
are a number of predisposing factors that contribute to
this disease. The uterine muscles may have lost their
ability to contract, or the broad ligaments that hold the
uterus in place may have stretched from the mare having
many foals causing the uterus to fall lower in the
abdomen. Reproductively healthy mares clear the fluids of
breeding by gravity flow because their uterus is located
high in the abdomen. Mares with persistent endometritis
can not clear the fluids because the uterus is slung low
in the abdomen.
Unfortunately, it is expensive to accurately diagnose
this condition. An owner may take the mare to a
university or private veterinary clinic that has
scintigraphy equipment. When the mare is in heat a
radioactive substance can be infused into her uterus and
the amount of radioactivity that remains in the uterus
after two hours can be measured. If the mare is normal,
she will clear 50% of the radioactive substance. If she
has a delay in her ability to clear the uterus, she will
clear virtually nothing. The veterinarian can ultrasound
the mare's uterus 24 hours after she has been bred to
determine if she is retaining fluid. If there is fluid,
treatment should be performed at that time. However, the
mare may not conceive because the inflammation has been
present for too long.
Treatment is aimed at making the uterus contract so
that the mare pushes the fluids out. This can be
accomplished with drugs such as oxytocin and
prostaglandins. Prior to injection of the drug, the
veterinarian may want to lavage the uterus with fluids to
remove the pus. Treatments are conducted early after
breeding--four to eight hours--so that the pus does not
remain in contact with the uterine lining for a long
time. The longer pus remains in the uterus, the more
inflammation it causes and the longer it may take the
uterus to heal. The veterinarian waits four hours so that
the sperm have time to reach the oviduct.
A second examination with ultrasound is conducted 24
hours after breeding to determine if there is any fluid
left in the uterus. If there is, a second injection of
oxytocin is administered.
Prognosis for pregnancy is extremely variable for this
group. For example, if you breed and treat a mare
properly the first time, her chance of foaling is greater
than with a mare which has been bred four cycles prior to
treatment. This mare has had more insult during that
breeding season, so by the time the veterinarian sees
her, her chances of conceiving are poor.
For any of the three categories of "dirty
mares," the best prevention is to have your mare
checked by a veterinarian in the fall, then bred using
good management techniques and treated properly early in