Equine Reproduction
Dr.
Jack Sales, DVM
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.