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5
EQUINE MATTERS
THE PROB L EM MARE
Liz Mitchell MA VetMB CertEP MRCVS,
Scott Mitchell Associates
Breeding
from the problem mare
Veterinary Surgeon
Liz Mitchell
XLVets Equine Practice
Scott Mitchell
Associates
The problem mare has below normal fertility.
The pregnancy rate per cycle
is on average around 65% with natural covering, 50% with chilled semen Artificial
Insemination (AI) and 40% with frozen semen AI. This means many normal mares
may take two or three cycles to become pregnant.
The role of the fertility of the stallion and
correct timing of the mating or insemination
cannot be underestimated. It is important to
choose a stallion with a proven fertility record
and ensure the mare is regularly examined
or teased through her cycle to ensure the
optimum timing for mating or insemination.
With AI and in particular with frozen semen
it is vital that insemination takes place very
close to ovulation due to the limited lifespan
of the semen. Provided that the stallion's
semen is of adequate quality and the timing
of mating/insemination is correct then
fertilisation rates in the mare are very high
(in excess of 90%) even in the older brood
mare. It is an unfavourable environment in
the uterus that is often responsible for the loss
of the early embryo leading to the much
reduced pregnancy rates at first scan. The
treatment of the problem mare is usually
aimed at improving the uterine environment.
The uterine environment
The uterus is protected from the outside world
by three important seals: the cervix, the
vestibular seal and the vulval lips. Each of
these has an important role in preventing the
entry of unwanted bacteria and air from the
outside to protect the uterus from infection. It
is also necessary that these structures: allow
entry of the stallion's penis if natural service
is used; allow the exit of the inflammatory
fluid and bacteria that inevitably follow a
mating/insemination; stretch to allow the
passage of the foal during the birth process.
Vulval abnormalities
Some mares, in particular thoroughbreds,
older mares and those in poor body condition
have sloping vulval conformation. Faeces are
deposited into the vulva and commonly some
air and bacteria are sucked in leading to a
continuous and low grade infection within
the vagina. This can spread upwards to
cause inflammation in the uterus (endometritis).
Caslick's sutures can be inserted into the
vulval lips to provide an artificial seal and
help prevent the entry of bacteria and air.
Vaginal abnormalities
In some mares, particularly following foaling,
the vagina may slope towards the cervix and
lead to urine pooling in this area. This causes
a chemical irritation and inflammation of the
vagina and uterus.
Cervical abnormalities
The cervix may be torn or damaged during
a previous foaling. The absence of an
effective seal at the cervix contributes to
fertility problems. There is no specific treatment
but the condition may improve over time. In
older maiden mares the cervix may be firm
and fibrous and fail to relax adequately when
the mare is in season. This may prevent a
successful mating and can also prevent the
normal release of fluid and bacteria from the
uterus following mating, leading to fluid
accumulation in the uterus (post covering
endometritis). In some cases the cervix can be
manually dilated when the mare is in season
to assist with this problem.
Uterine abnormalities
Endometritis is the inflammation of the
lining of the uterus (endometrium) with the
presence of fluid and/or bacteria. This is
the most common cause of reduced fertility
in the mare. The factors that contribute to
the development of the condition are
failures in the vulval and cervical seal and
the failure to clear inflammatory fluid and
bacteria present in the uterus following
mating/insemination or foaling. Some
older mares develop a very marked
reaction in the uterine lining associated
with being in season and have poorer
uterine clearance mechanisms; these
mares tend to accumulate more fluid in the
uterus during their season and following
covering which can affect their chances of
becoming pregnant.
A diagnosis of endometritis is made on
detection of fluid in the uterus on rectal
ultrasound scan and/or the presence of
bacteria and inflammatory cells on
endometrial swabs and smears.
Endometritis