Swine Breeding
MU Guide
Artificial Insemination in Swine:
Breeding the Female
Jodi Sterle and Tim Safranski
Department of Animal Sciences
Artificial insemination (AI) in swine is not a new
technique. There are reports as early as the 1930s of
collecting semen for insemination. However, use of
AI in the United States has skyrocketed in the past
decade. It is important to remember that AI is a tool
that will work for your operation only if you are willing to manage and use it properly.
One of the disadvantages of AI is that it may
require a higher level of management than some
natural-service mating systems. For example, there is
a greater chance of human error associated with AI
than with natural service. When a boar naturally
mates a sow, the semen is not subjected to severe
changes in environment and is generally deposited
into the female more than once during a period that
spans the optimal time for fertilization. In contrast,
many environmental changes are possible when
semen is collected, diluted, transported and then
deposited artificially. The inseminations must be done
correctly and at the optimal times. To obtain a high
conception rate and litter size, estrous detection (heat
checking) must be done carefully and without fail.
Sanitation of the equipment as an important consideration in all AI procedures. Today it is possible to
handle semen using all disposable materials, which
alleviates the need for rigorous sanitation of equipment. When a conscientious effort is made to consider
and incorporate these practices, AI can work on any
Perhaps the greatest advantage of AI is that it
permits you to make greater use of new, superior
genetics at a potentially lower cost than some
natural-service systems and with less risk of disease
transmission. Purchasing semen allows genetic
diversity, which can be used to optimize crossbreeding systems on smaller farms, and increased genetic
progress. This can be achieved without the expense
of purchasing and maintaining a single, superior
boar. Additionally, good boars can be used more
extensively than those used for natural service,
because AI increases the number of inseminations
per ejaculate.
Swine estrous cycle
The estrous cycle in the pig averages 21 days but
can range from 17 to 25 days. The first day of standing heat, when the female is receptive to the male and
will stand to be mounted, is referred to as day 0. The
two or three days that the female is sexually receptive
is termed estrus. The standing reflex is stimulated by
contact with a mature boar. The boar’s submaxillary
salivary glands produce pheromones that are secreted
into the saliva. Direct physical contact is the best way
to ensure that these stimulatory chemicals are transmitted to the female. The pheromones signal to the
female that a mature boar is present and initiate the
standing reflex if the female is in estrus. The female
may or may not also exhibit other visible signs,
including mounting or attempting to ride other
females, a swollen, red vulva, mucus from the vulva,
“popping” of the ears, and increased vocalization and
activity. In gilts, estrus may last only a day or two,
while a sow may be in estrus for three days. Although
ovulation (release of the egg from the follicle on the
ovary) usually occurs 23–48 hours after the onset of
estrus, this event is extremely variable. In fact, a sow
may ovulate before estrus occurs. It is for this reason
that producers generally inseminate females more
than once.
Detecting estrus
The importance of estrous detection in an AI system cannot be overemphasized. It is absolutely vital
to the success of each breeding for the producer to be
accurate in estimating the onset of estrus. Twice-daily
estrous detection is more effective than once-daily
detection, although it is also more time- and laborconsuming. The challenge with twice-daily estrous
detection is that the benefits can be realized only if
both checks are done properly and as close to 12
hours apart as possible. The frequency of estrous
detection will determine the accuracy of estimating
the onset of estrus. For greatest efficiency, estrous
detection should be done first thing in the morning,
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before feeding or at least an hour after feeding. If this
is not possible, the afternoon or early evening can
work if the ambient temperature is not too high. The
principle is to perform estrous detection when gilts
and sows are not distracted or frustrated. Estrous
detection should be conducted in a neutral pen with
females in groups of 12 or less. By taking both the
females and the boar to a novel pen, you will optimize the accuracy of estrous detection. This is an
especially important aspect of estrous detection in
gilts. With sows in gestation crates, a boar should be
blocked in the aisle in front of four or five sows at a
time for individual contact and to ensure that the
technician is able to observe all sows for estrus before
they become refractory. Pressure can be applied manually to the sow’s back while in the presence of the
boar to determine estrus. The boar will generally
chant, salivate and attempt to mount most of the
females. A female in estrus may seek out the boar and
will stand to be mounted. Once a female is detected
as being in estrus, she should be removed from the
pen so the boar will circulate to the other females.
It is critical to mate the female within a few hours
before ovulation. However, timing of ovulation
varies. Gilts will generally ovulate sooner after the
onset of estrus than sows. There is also variation
among farms, genetic lines and individual females.
Because sows stand longer than gilts and because
ovulation in both sows and gilts occurs near the end
of esturs, it is recommended that with twice-daily
heat checks, gilts be inseminated 12 hours after detection of estrus and sows be inseminated 24 hours after
detection of estrus. With once-daily heat checks, the
accuracy of estimating the onset of estrus decreases;
therefore gilts and sows are usually bred when they
are found in estrus. As patterns of expression and
duration of estrus are established for a given farm it
may be possible to refine the timing and number of
inseminations. Additionally, it is recommended that
all females be mated once daily each day they stand.
While this potentially results in some waste of semen,
it is the best way to ensure that at least one mating is
optimally timed relative to ovulation.
Figure 1. Reproductive anatomy of the sow.
Source: After E. S. E. Hafez, ed. 1974. Reproduction in Farm
Animals. Philadelphia: Lea and Febiger.
the uterus. During estrus, the cervix becomes swollen,
which allows the AI spirette or catheter to be
“locked” into it. (“Spirette” refers to a spiral-shaped,
plastic-tipped insemination rod; “catheter” refers to a
foam-tipped insemination rod.) This prevents some
semen backflow and initiates uterine contractions,
which are essential for sperm transport through the
uterus to the oviduct, the site of fertilization. The
ovary releases the eggs (oocytes) during ovulation
and the oocytes enter the oviduct. In natural mating,
the boar’s penis (which is corkscrew-shaped) fits into
the folds of the cervix, and the pressure causes the
penis to begin ejaculation. The semen travels through
the uterus with the help of uterine contractions signaled by the presence of the penis in the cervical folds
and into the oviduct, where it combines with the egg
(fertilization). Freshly ejaculated sperm are not capable of penetrating an egg and must be present in the
female reproductive tract for two to three hours to
undergo the biological changes necessary for fertilization. This process is referred to as sperm capacitation.
Inseminating the female
The female reproductive system
The reproductive system of female swine is more
conducive to AI than that of cattle or sheep, and
therefore AI is less time-consuming and easier to
accomplish in swine. Still, the proper technique and
an understanding of the system are important for best
results. Figure 1 shows the reproductive organs of the
female. The vulva is the visible portion of the female
reproductive tract and may be red and swollen before
or at the time of standing heat. The vulva leads to the
vagina, which tapers into the cervix. The cervix consists of multiple ridges that act as a barrier to prevent
bacteria, dirt and other foreign material from entering
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• It is a good idea to evaluate semen with a microscope before using it (guidelines for evaluating
semen are published elsewhere). Shipment, dilution, storage temperature, fluctuations in temperature and length of time since collection may all
affect the shelf life, motility and viability of the
• Before inseminating the female, use a paper towel
to clean the vulva.
• Lubricate the tip of the spirette or catheter using
any nonspermicidal lubricant or a few drops of
extender. Take care to avoid getting lubricant in
the opening of the spirette/catheter.
• Gently guide the spirette/catheter, with the tip
pointed up, through the vagina to the cervix (see
Figure 2. Insert the spirette or catheter at an upward angle to
avoid coming in contact with the bladder.
Figure 3. Use a counterclockwise rotation to insert the spirette
or catheter into the cervix.
Figure 2). The bottle of diluted semen is not
attached to the spirette/catheter at this point.
Keeping the tip of the spirette/catheter up minimizes the chance of coming in contact with the
bladder, which could cause a backflow of urine
into the spirette/catheter. If this happens, a new
spirette/catheter is needed, because urine kills
sperm. This is the primary reason the bottle of
diluted semen should not be connected to the
spirette/catheter until the cervix has been
entered. Another reason is to avoid exposing the
bottle unnecessarily to extremes of light or temperature. When using the cochette system instead
of a bottle, it is common to attach the cochette
first because of the dexterity required in doing so.
• When using a spirette, a counterclockwise rotation will insert the spirette into the cervix (see
Figure 3). At this time, resistance can be felt by
gently pulling back on the spirette. When using a
foam-tipped catheter, the catheter is not always
inserted into the cervix. Instead, the catheter is
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positioned up against the cervix. However, some
breeders push gently in an attempt to insert the
foam tip into the first cervical ring. If the foam tip
is securely locked in the cervix, resistance will be
felt when the catheter is rotated.
• Gently invert the bottle of diluted semen two or
three times to mix the semen. Attach the bottle to
the end of the spirette and discharge the semen
slowly. A gentle squeeze to start the process may
be needed, but after that the semen should be
allowed to be taken up by uterine contractions.
This process will usually take at least three minutes. Because of the variation in intensity of uterine contractions, gilts will usually take longer to
inseminate than sows. Depositing the semen too
rapidly will cause a backflow of semen out of the
vulva. Obviously, semen that flows out onto the
ground is wasted. Remember that you are
attempting to replace the boar, which spends five
to ten minutes at each breeding.
• A small amount of backflow is expected. If an
excessive amount of backflow occurs, stop. Either
the semen is being deposited too rapidly (the
semen needs to be deposited at a slower rate) or
the spirette is not locked into the cervix. If semen
flow stops, reposition the spirette by turning it a
quarter of a turn (if you are using a foam-tipped
catheter, move it gently back and forth) to reinitiate semen flow. Additionally, using sidecutters or
a pocketknife to cut a hole in the semen bottle can
be helpful if flow has stopped because of a vacuum buildup.
• If there is a great deal of resistance to the flow of
semen, reposition the spirette, because the tip
may be lodged against a cervical fold.
• Semen transport, and therefore fertilization, can
be inefficient when females are frightened or disturbed; females should always be handled calmly
and gently. The breeder is trying to mimic the
boar, and greatest fertility occurs when this is
done well. Having a boar present, applying some
back pressure and massaging the female’s flank
during insemination may increase the number or
intensity of uterine contractions that draw semen
from the bottle and transport it into the uterus.
This is especially true in breeding gilts. If the
female has been “locked down” and stands to be
mounted for a long period of time, she may
become refractory (that is, she may no be longer
be able to stay in the “locked down” position). If
this happens, simply remove the female from the
boar’s presence for at least an hour and then try
again. It is important that the female initiate the
standing reflex while being inseminated; this elicits the uterine contractions that are vital for
sperm transport.
• When all of the semen has been deposited into
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the female, remove the spirette by rotating it
clockwise while gently pulling. Some people prefer to leave the catheter in place for several minutes to prolong cervical stimulation.
• A new spirette/catheter should be used for each
insemination to eliminate the possibility of transmitting a disease or infection from one female to
the next.
• Keep the female in quiet surroundings for 20–30
minutes. Distress at this time may still disrupt
semen transport and fertilization.
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For more information
The Swine AI Book: A Field and Laboratory Technicians’
Guide to Artificial Insemination in Swine.
Tim Safranski is a State Extension Swine Specialist.
Jodi Sterle is a graduate research assistant in animal
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Department of Agriculture. Ronald J. Turner, Director, Cooperative Extension, University of Missouri and Lincoln University, Columbia,
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