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Copyright
2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any
editorial material, artwork and photos is strictly forbidden without
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Best
Management Practices for Breeding a Mare
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Washington
State
University
College
of Veterinary Medicine Equine News – Winter 2010
[Reprinted with Permission]
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February
2010 Issue
Breeding season for horses usually occurs in the spring. This
makes winter a good time for breeders to plan for the upcoming season.
Though people have many reasons for breeding a horse, whether for
commercial purposes or as a hobby, there are some important factors that
all breeders should consider before getting started.
The mare’s age is important,
as well as the number of pregnancies and foals she has produced in the
past. Older mares that have not had a foal may have more difficulty
becoming pregnant. Mares with a history of abortion or pregnancy with
twins may be categorized as high risk.
Also
consider the mare’s health and if she is in good body condition. Does
she have any potentially heritable disorders? Does she have any
musculoskeletal problems that carrying a foal would exacerbate, such as
lameness due to tendon injuries or arthritis?
“Another question horse
breeders should ask themselves is why they want to breed this mare, in
particular, when so many unwanted horses are out there,” said Dr. Lisa
K. Pearson, a
Washington
State
University
large animal theriogenology resident.
“If an owner would be just
as happy adopting or rescuing an adult horse for training, showing, or
pleasure riding, then perhaps bringing another horse into the world
would not be to their advantage. Also, will the owner accept
responsibility for the foal for its lifetime? If the foal is to be sold,
will there be provisions that if that new owner cannot keep it, it can
be returned to the breeder? If it is to be raised and used by the
breeder, will they provide for it regardless of the foal’s potential
use as an athletic animal? All of these questions should be addressed
before a mare is bred.”
Dr.
Lisa Pearson performing a transrectal ultrasound examination for
diagnosis of pregnancy in a mare. Dr. Pearson is the newest theriology
resident on the WSU equine team.
Breeding
soundness evaluations
Once the decision is made to
proceed, it is essential that the owner involve a veterinarian from the
very beginning. First, a breeding soundness evaluation (BSE) should be
performed to assess the mare’s reproductive potential. This important
examination has several components. Mares undergo a physical
examination, including an assessment of the conformation of the mare’s
perineum (the rectal and vulvar area). Transrectal palpation and
ultrasound of the reproductive tract are also performed to assess where
the mare is in the estrous cycle and to evaluate any pathology, such as
abnormalities of the ovaries, uterus, cervix, vagina, or bladder. Mares
are seasonally polyestrous, meaning that they have a distinct breeding
season.
“Ideally, we’d like to see
mares bred from March to June but there are techniques for extending
this window,” Dr. Pearson said. “Some mares may cycle year-round.”
A BSE also includes sample
submission for laboratory analysis. Uterine culture and cytology are
used to screen for infection or inflammation, and a uterine endometrial
biopsy can provide information regarding the potential of the uterus to
carry a foal to term.
“Owners should schedule the
BSE with their veterinarian early in the season, as mares may need
treatment for any diagnosed conditions,” Dr. Pearson said.
“Additionally, starting early allows for several cycles to pass to try
and establish a pregnancy. The BSE is a very important and common
examination that is performed here at WSU on a regular basis. One
advantage we have here is that we have a laboratory on-site to examine
samples, so we can get results faster than those who have to ship them
to a laboratory.”
Tracking
a mare’s cycle
Once a mare is judged
reproductively sound, the next step is tracking her cycle. This is best
done using ultrasound to examine the ovaries and uterus. One examination
will not provide enough information to know when a mare should be bred.
Typically, examinations are performed several days apart until a
dominant follicle is established on one or both ovaries. Thereafter,
daily ultrasound examinations may be needed to accurately time
insemination. Insemination can be accomplished through artificial
insemination using fresh cooled semen or frozen semen, or by live cover.
“Assuming we are using fresh
cooled semen,” Dr. Pearson said, “once the mare has a sufficiently
large follicle, she can be induced to ovulate by injecting commercial
hormone preparations. Ovulation will usually follow within 36 hours.
Insemination is timed around ovulation, and usually two doses of semen
are administered, once before and once after ovulation. Ultrasound
examinations are performed after insemination to ensure that ovulation
occurred, and to assess the amount of post-insemination inflammation in
the uterus.
“All inseminations cause
inflammation,” she said. “Some mares, however, tend to have more
severe reactions than others, causing the uterus to accumulate fluid. If
this fluid remains when the embryo travels down the oviduct to the
uterus, the embryo will not survive. Veterinarians can lavage or flush
the uterus with sterile fluid solutions and administer the hormone
oxytocin to help remove fluid from the uterus.”
A pregnancy diagnosis can be
made 12-14 days after breeding. Ultrasound is used to visualize an
embryonic vesicle. If the mare is not pregnant, she will return to
estrus usually within one week. A mare’s cycle is 21 days long, so she
may be developing a new dominant follicle which can then be tracked. A
mare can also be “short-cycled” if she is not pregnant, meaning that
an injection can be given to hasten the next heat. This typically causes
an advancement of approximately five days.
If the mare is pregnant, the
veterinarian will check for the presence of one or two embryonic
vesicles, and if two are present (twins), the veterinarian will discuss
options with the owner. Twins have a very high rate of abortion, and
twins that survive to birth are usually smaller, weaker, and may require
extensive medical care.
If one vesicle is seen, the
veterinarian will make a schedule with the owner for subsequent
evaluations: 25-30 days of gestation to assess the fetal heartbeat; 45
and 60 days to assess health of the pregnancy, and periodically in mid
to late gestation (gestation is on average 342 days). The highest rate
of pregnancy loss is before 60 days of gestation. Determining the
foal’s sex may be done between 60 and 70 days of gestation. Blood
drawn from pregnant mares can be analyzed for serum progesterone levels,
the hormone that maintains pregnancy. Mares with low progesterone levels
can be supplemented orally.
“Working
closely with a veterinarian ensures a mare has the best chance of
becoming pregnant, and will not be bred needlessly if she has any
problems that may prevent her from becoming pregnant,” Dr. Pearson
said. “Planning ahead ensures that when breeding season arrives,
owners have a good idea of what to expect both for their mare and from
their veterinarian.”
Copyright
2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any
editorial material, artwork and photos is strictly forbidden without
express written permission of the publisher. For information about
reprint rights, please contact the editor; editor@rockymountainrider.com.
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