Breeding from your mare
Understanding the basic physiology and anatomy of your mare will
help you understand what is involved in successfully breeding
healthy foals.
Reproductive Anatomy:
Mares have two ovaries. The ovaries are situated in the dorsal
(upper) part of the abdomen, just behind the kidneys. The ovaries
are the female gonads and they produce and release eggs. They
are also the site of production of the female sex hormones
oestrogen and progesterone. The uterus (womb) is comprised of
two horns and a body, all being suspended from the roof of the
abdomen by the broad ligament. The cervix protects the entrance
into the uterus from the vagina.
Figure 1: The mare’s reproductive system
Figure 2: The mare’s reproductive system in situ
The oestrus cycle:
In the Northern Hemisphere mares are most sexually receptive
and active from April through to September. During winter, mares
become sexually inactive and are said to be in a state of
anoestrus. As spring approaches and day light length increases,
the pineal gland within the brain produces less of the hormone
melatonin and the mare enters a transitional period. (Sometimes
mares can exhibit intermittent grumpy behavior during the
transitional period.) With rising hormone levels, follicles within the
ovaries are stimulated to grow. Initially lots of follicles grow
simultaneously until one becomes dominant and ovulates
releasing the egg from the follicle. Following this, regular oestrus
cycles will occur throughout the summer months.
Each oestrus cycle lasts around 21 days with the mare being in
season (sexually receptive) for 3-8 days. During this time the mare
will show variable behavioural changes such as frequent posturing
(see below) and she will also be receptive to the stallion, allowing
him to nuzzle her.
Figure 3: Mare in season
These behavioural changes occur due to increasing levels of the
hormone oestrogen, which is released from the follicles. Ovulation
usually occurs 24-48 hours before the mare goes out of season
and what remains of the follicle after ovulation forms a structure
within the ovary called the corpus luteum (C.L). The C.L. produces
another hormone called progesterone. Simply speaking
progesterone has the opposite effect to oestrogen and the mare
will now be out of season and no longer receptive to the advances
of the stallion. At around 16-17 days, if a pregnancy is not
detected, the lining of the uterus produces a hormone called
prostaglandin, which destroys the C.L. and consequently the levels
of circulating progesterone decrease. This reduction in
progesterone allows follicles to develop again and then the mare
returns to season. However if the mare is pregnant the C.L. will
remain and with the help of other hormones, the pregnancy will be
supported and there will be no return to osetrous.
Preparing your mare for stud
Prior to sending your mare to stud there are a number of things
that need to be considered, such as her having a veterinary
examination to ensure that she is fit to breed.
In order to perform this safely your veterinary surgeon may require
stocks, although quiet, well-behaved mares can be assessed over
a stable door.
A typical breeding soundness examination includes:
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A physical examination
Rectal examination
Ultrasound scan
Reproductive examination
At the same time as the breeding soundness examination the
veterinary surgeon will also perform clitoral swabs in order to make
sure that the mare is free from the bacteria (Taylorella
equigenitalis), which causes the venereal disease Contagious
Equine Metritis (CEM). Blood tests are also performed to rule out
viral infections, namely Equine Viral Arteritis (EVA) and Equine
Infectious Anaemia (EIA) prior to entering the stud.
Pre-stud checklist
Before sending your mare to stud you will need to consider
whether the following are required and up to date:
Vaccinations (tetanus, influenza and herpes virus (many
studs stipulate that horses are vaccinated against equine
herpes virus in order to minimize the risk of abortion storms)
• Worming
• Dental health
• Routine hoof care
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Overall physical condition of the mare
Most stud farms will impose a 2-week period of isolation for any
new arrivals. This allows new arrivals to be monitored for any
infections, which they may be incubating, which they may not have
been tested for, thus safe guarding the stud farm from potentially
serious infections. If your mare is pregnant and you are sending
her away to stud to foal, then you should contact the stud for
further information, as the mare may well need to arrive at the stud
at least 3-4 weeks prior to her foaling date.
Central Equine Vets can provide you with further information on
both what is involved with a breeding soundness examination as
well as providing advice on appropriate considerations for breeding
your mare.
Mating
Mares can be mated or “covered” in one of two ways:
1. Natural mating with a stallion
2. Artificial insemination (A.I.)
With artificial insemination semen is collected from a stallion,
which maybe from a different part of the country or a different
country all together, thus giving you, the breeder, a wider range of
choice of sire. The collected semen is then stored, and at a later
date, placed into the uterus of the mare.
Mares are often covered naturally, especially in the thoroughbred
industry.
Advances in equine reproductive knowledge and techniques mean
that it is now possible for a veterinary surgeon to examine the
mare to see what stage of her oestrous cycle she is in. Using
modern hormone drugs it is then possible to manipulate the mare’s
oestrous cycle in order to induce ovulation and thus mate the mare
as close to the ovulation as possible. This means that fewer
matings are required.
Artificial Insemination (A.I.)
A.I. involves collecting semen from the stallion and then implanting
it into the mare. The semen is collected by having the stallion
either mount a teaser mare or dummy. Once mounted, the stallion
ejaculates into an artificial vagina (A.V.), and the semen is
collected. From here it can be used immediately or it maybe
chilled, or frozen, and then transported to the stud farm where the
mare is stabled.
The mare is then inseminated once she is in season. The semen is
thawed (if frozen) and inserted into the mare’s uterus through the
vagina and cervix via an A.I. gun (pipette).
Advantages of A.I.?
Reduced risk of spreading venereal diseases as there is no
direct stallion-mare contact
• Reduced risk of injury to the horses and handlers compared
to natural mating
• Achieves mating whilst the sire and dam are on different stud
farms, or even in different countries
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If you are considering breeding from either a mare or stallion
Central Equine Vets will be able to provide you with further advice
as to which method is most appropriate for you.