Equine Reproduction
LESSON FIVE
Infertility in the Mare
Assignment:
Read Chapter 6 in the text.
In this lesson
we will study the most common causes of mare infertility.
Mare
Infertility
What is normal
fertility? The following are the rules of
thumb regarding expectations at a well-run breeding farm using natural cover or
artificial insemination.
1. A 50% pregnancy rate is considered normal
after a group of mares are
bred through
their first estrus or heat cycle (single estrus).
2. An 80-85% pregnancy rate is considered a
normal range in a group of
mares bred during
a breeding season.
3. A pregnancy loss of 10-12% on well-managed
horse farm is not
abnormal.
4. If you have 100 mares, the average will be
80-85% pregnant at 40
days and 70-75%
will produce a live foal.
5. Early embryonic loss is a major factor in
fertility losses in sub-fertile
mares. A 60-70% loss prior to day 14 can be
expected.
6. Early embryonic loss on an average group of mares
is considered to
be 10 to 15
%. These are detectable losses generally
after 14 days of
pregnancy.
I. Non-infectious causes of infertility
A. The
mare not in heat so we assume she can’t be bred.
1. The mare may be pregnant; be sure and rule
this out in all
situations.
2. Persistent CL: prolonged diestrus/pseoudopregnancy.
The
cause may be :
a. Early
embryonic death.
b. Treat
with prostaglandin.
B.
The mare is sterile, unable to conceive.
a. Genetic
abnormalities.
- The
mare is out of season.
1. The Transitional Phase is a period of
infertility (anovulatory
cycles).
2. Winter Anestrus is a period of
infertility. Keep in mind about
15 to 20% of mares will cycle year around.
3. The above two problems can be addressed by
use of a light
program. Put the mare under 16 hours of light daily
usually
starting in early
December.
4. Ovarian
shutdown is a possibility.
a. Usually
occurs in a small percentage of mares (1-2%) that
have just foaled,
or in every other year mares. Use of a
light program or
prostaglandin injections are usually not
helpful in these
cases.
b. Mares
nearing 25 years of age are often hard to get in foal
and there is very
little which can be done to improve
these mares’
reproductive status.
c. Nutrition
induced problems seen in low body condition
score – negative
energy balance. Obviously, increasing
the level of
nutrition in these mares will improve their
reproductive
status.
D.
Behavioral Anestrus.
1.
Silent heat.
a. The mare may not
like the stallion. Occasionally a mare
will
not respond to a particular teaser for behavioral
reasons.
b. The
mare may be protecting the foal; a behavioral
problem seen
often first foal mares.
c. A mare may not like her new environment
(newly arrived
mares) and
therefore may not show signs of estrus even
though she may
have a normal follicle.
d. Treatment:
Palpate if suspicious of silent heat in order to
determine the
true state of the ovaries, uterus, and
cervix, making
sure the mare is not pregnant.
E.
Anatomical Defects.
1. The vulva is tilted or the anus is
sunken. These conditions
lead to uterine
infections.
2. Urine pooling usually prevents pregnancy due
to infection
and/or sperm
death.
3. Windsucker is the same tilted vulva.
4. Cervical adhesions or cervical tears prevent
sperm from
entering the
mare’s reproductive tract due to cervical stricture.
If the mare does conceive and the cervix
cannot close tightly
due to cervical
tears, the mare cannot stay in foal.
5. Anything that will blocks
the ability of the sperm to travel up
the tract to meet
the ovum.
F.
Tumors or cysts associated with the reproductive tract.
1. Granulosa
Cell Tumor.
a.
The mare acts like a stallion because the tumor produces
testosterone.
b.
An extremely large ovary which could be the size of
basketball)
c.
Treatment includes surgical removal; the opposite ovary
will start
functioning normally.
2.
Melanoma.
a. Seem in old gray
mares.
b. Tumor
usually just causes irritation of reproductive tract.
Equine Cutaneous melanoma
The melanoma above would be a rare
occurrence, and in this case would obviously affect fertility.
3.
Uterine cysts.
a. Usually
seen in older mares.
b. Treatment
includes laser removal which improves
fertility.
II
Infectious Causes of infertility
A. Endometritis (metritis/uterine
infection). This is the most
common cause of
infertility in the mare.
1. Inflammation or infection of the inner lining
of the uterus
a.
Bacterial is the most common.
b. Fungal infection
is not nearly as common as
bacterial; in fact, it is quite rare.
2. Diagnosis
A culture plate with sensitivity disk
A. Culture and sensitivity test taken prior to
breeding.
1. Sometimes this is done routinely as 33% of
normal mares
have been shown
to culture positive during estrus by one
study.
2. Usually a requirement by the breeding farm on
all barren
and maiden mares.
B.
Culture and sensitivity tests in problem mares.
1. If a mare fails to conceive after two cycles,
a culture and
sensitivity is
indicated.
2. If the mare is showing abnormal discharges a
culture and
sensitivity is
indicated.
3. On palpation or ultrasound a doughy,
thickened uterus,
fluid in uterus
or lack of normal involution in the foaling
mare, a culture
and sensitivity is indicated.
Placing a catheter into the uterus for infusion
3.
Treatment Options
a. Intrauterine
infusions of appropriate antibiotics
(according to sensitivity testing) of 60 to 500
milliliters, often added to saline.
b.
Intrauterine lavage: large volumes of
sterile saline
to flush debris
out of uterus and stimulate normal
uterine
immunity. Generally 1
to 2 liters.
c.
Prevention starts with good hygiene in
breeding
shed, in chute
area and at foaling.
d.
Make sure there is no venereal
disease
transmission from
stallion to mare.
e. Antibiotics
during artificial insemination
(antibiotics
added to semen extender) can be
helpful in
controlling mild infections or
contamination
during the breeding process.
Assignment: Please
send your answers to Dr. Sales at jsales@horsecoursesonline.com
1. What is the difference between persistent
post mating endometritis and chronic infectious endometritis.
Detail how each is managed or controlled.
2. What is the
procedure for obtaining a uterine culture and sensitivity, when is it necessary
and what can it tell you?
3. List at least 4
different forms of intrauterine therapy used in chronic infectious
endometritis.