WHAT IS A SEMEN TANK?

Association of Waterloo, Ontario, became the first breeding
organization in the world to operate a 100 percent frozen
semen program.
Today, practically all livestock semen in the United States
is handled in the deep frozen form, and is stored in semen
tanks.
Proper removal of semen straws from inside of a semen tank.
T
he practice of artificial insemination has been traced
back to ancient Arabian horsemen. The first scientific
A.I. research was conducted by Italian physiologist
Spallanzani in 1780. Spallanzani attained success with
amphibious animals, and successfully artificially
inseminated dogs. In 1782, he discovered the fertilizing
power of semen resided in the sperm carried by the
spermatic fluid.
Spallanzani found the effect of cooling on the length of
sperm life. He recognized that freezing stallion semen in
snow or cold temperatures did not kill the sperm, but held
them in a state of suspended animation until exposed to
heat, where they resumed movement.
In the beginning of the twentieth century, A.I. took off in
Russia where massive attempts were taken to upgrade and
expand the country’s livestock population. Semen diluters,
artificial vaginas, electro-ejaculation and transportation of
frozen semen were developed in Russia as the value of A.I.
was understood and put into practice.
In 1949, Dr. Christopher Polge uncovered a practical
method for long-term preservation of semen by deep
freezing at -79° C using dry ice. Shortly after the use of dry
ice began, liquid nitrogen (LN2) was introduced, chilling
semen to temperatures of -195° C or -320° F.
In December 1954, the Waterloo Cattle Breeding
WHAT IS A SEMEN TANK?
A semen tank is a storage unit which uses liquid
nitrogen to keep livestock semen frozen at temperatures of
-320° F. The semen tank is built on the same principle as
the thermos canister with double-walled construction and
an evacuated space between the inner and outer walls.
Sir John Dewar discovered that a properly insulated
vacuum space can be created between an inner and outer
container. LN2 can be contained and stored for long periods
of time, making these tanks ideal for containing this gas.
WHY IS LIQUID NITROGEN USED AS A COOLANT FOR
SEMEN TANKS?
• Its -320° F temperature is excellent for efficient
storage of frozen semen.
• It is a relatively inexpensive refrigerant.
• It has excellent physical properties, being relatively
inert, not supporting oxidation or combustion. It is a
safe substance, but precaution should be taken when
handling and contact with bare skin should be
avoided.
The inner shell is an unwelded, one-piece aluminum
container. This assures maximum temperature equalization
throughout.
As the liquid nitrogen evaporates, vapors form in the
inner shell and are as cold as the LN2 itself. Therefore, a
container that is half full of LN2 will be equally as cold
throughout.
THE CARE AND MAINTENANCE OF SEMEN TANKS
Pulling a proper vacuum is
the key component in
producing a long-lived semen
tank for seven to ten years.
The outer shell of a tank is
aluminum and is well suited
to take the punishment of
daily wear-and-tear around
the farm.
Special consideration has
Cutout of a semen tank,
been given to the neck design
viewing the inner shell.
of semen tanks to achieve a
balance between the strength required for field service and
low heat conduction essential for a long holding time.
Necks are made of fiberglass-epoxy, meeting both of these
requirements. Heat flows down the fiberglass-epoxy neck,
and a foam plug intercepts most of the heat before it
reaches the inner container. An important point to
remember is the entire inner shell of the container is
supported by the neck. It hangs like a pendulum and can
deflect during abusive use, so handle with care.
Liquid nitrogen continually evaporates unless it is stored
in temperatures lower than -320° F. A properly constructed
container will reduce evaporation to the rate that LN2 can
be maintained for one to six months, depending on the size
and model.
Constant temperature inside the unit is especially
important during times of extensive breeding. As a
particular canister is raised and lowered to allow the
removal of various canes or goblets, the frozen semen
could thaw and affect sperm motility. Keeping the
temperature at -320° F throughout the tank assures the
semen will not be subjected to temperature change.
DIFFERENT SIZE AND RANGES OF SEMEN TANKS
Semen tanks range in size from an in-the-field model
that holds 11 liters of liquid nitrogen to large storage units
that hold up to 1,400 liters of LN2. The livestock breeder or
A.I. technician should carefully assess the need of semen
storage capacity when purchasing a semen tank.
Field model - It is a good idea to consider using a smaller
container during times of concentrated breeding. Semen
can be transferred from large storage tanks to smaller
working units that are easier to transport to the breeding
site.
A container that holds 20 liters of LN2 will preserve its
coolant for 140 working days. Other advantages of a
smaller container include:
• Weight: an 11 liter tank weighs 37 pounds when full
and a 20 liter tank weighs 60 pounds when full of LN2.
• Storage capacity: 600 straws for both tanks
On-location storage model - Many breeders have the need
to store semen for longer periods of time. In this instance,
a container that can hold 33 liters of LN2 for 180 days of
working time is effective. This size container weighs over
90 pounds when full, but has excellent storage volume to
overall size ratio, and will hold 500 straws. To
accommodate the extended holding time, it has a small
neck opening with smaller canisters inside.
Permanent storage container - If the breeder is
collecting, processing and storing his own semen or has a
large cow herd, a container that holds 50 liters of LN2₂is
adequate. It weighs 120 pounds and holds 3,500 straws.
These containers should be refilled every 76 days.
USE OF A SEMEN TANK UNDER WORKING CONDITIONS
Special procedures should always be observed when
handling LN2
1. Nitrogen gas (the product
of LN2 evaporation) is
colorless, odorless and
tasteless. It can cause
asphyxiation in a confined
area that does not have
adequate ventilation. Always
use semen tanks in well
ventilated areas
2. Accidental contact with LN2
MVE Millenium 2000 XC 20
or LN2 vapors can cause a
freezing injury similar to a burn.
• Handle the liquid so that it will not splash or spill.
• Protect eyes with glasses, safety goggles or a face
shield.
• Wear protective gloves that can be easily removed
and long sleeves for arm protection.
• Pants should be worn outside boots to shed spilled
liquid.
• In the event of a burn from LN2, treat immediately for
frostbite.
3. When disposing of LN2, always dump it into an outdoor
pit filled with gravel where it will evaporate rapidly
and safely.
Remove the stick and briskly wave it in the air to speed
the condensation of frost which will appear on the part
that was submerged in LN2.
The livestock breeder should never allow the level of the
LN2 to be less than one inch from the bottom. A routine
refill schedule should be established with the breeder’s
liquid nitrogen supplier so a total loss of refrigerant does
not occur.
Liquid nitrogen costs anywhere from $.50 to $2 per liter,
and a medium-sized semen tank will hold 20 liters. The LN2
coolant will cost around $.10 per day as opposed to a
normal semen inventory value of more than $9,000.
FILLING A SEMEN TANK
1. The storage unit is filled by pouring liquid nitrogen
through the neck opening of the container or by using
a transfer tube from an LN2 storage container.
2. When filling a warm container with LN2, add the liquid
slowly at first to prevent the liquid from being carried
out by the high velocity stream of gas which blows out
the neck until the inner shell is cooled down. Fill the
unit about three-quarters of the way full and allow it to
continue cooling a few minutes. Then completely fill to
the desired level.
3. When starting with a warm container, the maximum
insulation efficiency is not reached until about 48
hours after filling. Therefore, the LN2₂loss rate will be
high for the first few hours and somewhat above
specification for the first two days. If maximum field
working time is needed, it is a good idea to “top off” a
semen tank from 12 to 48 hours after a warm fill.
4. Once the semen tank is filled, it should be visually
checked every day, and the LN2₂level should be checked
weekly.
CONTAINER STORAGE
Breeders have asked about the proper place for storing
their containers. Storage is recommended on a sturdy
wooden shelf or platform, in an area away from heavy
traffic.
If during inspection, the breeder discovers any abnormal
tank activity (frosting or sweating) he/she should
immediately take action to get another tank.
To check the LN2 level, the neck plug should be removed
and a wooden stick should be lowered to the bottom of the
unit. (Make sure the dip stick is resting on the bottom of
the inner container.) Leave the dip stick in the container for
five seconds.
WHY WOOD?
There are several reasons to use a wood platform. First,
wood can be dried easily, preventing an accumulation of
moisture under the container. This often happens when a
container is stored on a concrete floor.
Wood can cushion the container, softening the jolts of the
container movement, and helping to assure longevity.
The container should never be stored on straw or any
surface that has come into contact with animal urine or
feces. The acids contained in these materials can corrode
even a stainless steel surface. A single microscopic hole
can destroy the vacuum between the outer and inner shell.
Semen tanks should sit on a wooden structure off of the floor away from materials that could create microscopic holes in the tank.
THE CARE AND MAINTENANCE OF SEMEN TANKS
When the vacuum is depleted, the storage capability of the
tank is destroyed.
Special care should be exercised when transporting the
semen tank. It should never be allowed to tip over or rattle
around in the back of a pickup. Never drop or jar the
container.
The construction of the container is developed so the
weight of the inner shell is supported by the neck structure.
While this is a very strong connection, a sharp blow to the
container (such as an animal kick) can cause the inner
shell to act like a pendulum and crack the neck, releasing
the vacuum.
TROUBLE-SHOOTING
Because of the substantial investment stored in a
semen tank, there are several danger signs that should be
immediately recognized and acted upon to ensure high
quality.
Complete frosting of the outer shell - When the entire
outer shell of the semen tank frosts up, there has been a
sudden loss of the container’s entire vacuum. When this
occurs, the livestock breeder has a matter of hours to
transfer the semen to another storage container. The cause
of a complete loss is usually a major leak in the container’s
internal or external shell or a broken neck tube.
Ice spot on the outer shell - An isolated ice or frost spot
on the outer shell of the unit means that a “short” has
occurred between the inner and outer shell. This happens
when a dent compacts the insulation material and changes
it from a heat reflector to a heat transmitter.
The effect of a dent on the temperature inside the
container is minimal, but the container’s LN2 holding time
will be shortened.
Ice rising around the cap and top of the outer shell Frosting around the cap and outer neck area, is a sure sign
of a slow vacuum leak. This takes place in older containers
(seven to 10-years-old) as a result of vacuum decay, or
could be a symptom of faulty vacuum in a newer tank.
Holding time is adversely affected, and the owner should
have the tank evaluated and repaired.
Frost forming on the neck of a tank, a sign of a slow vacuum leak.
Broken goblet or dislodged canister - Sometimes the
breeder will “lose” a cane, straw, canister or goblet down
inside of the semen tank. In such cases, do not try to
retrieve these items yourself. Inform your Select Sires’ sales
representative; they are best equipped to handle this
problem without jeopardizing the quality of your semen
inventory.
Inventory - As with any well-managed business, you must
keep an accurate inventory and location of the items you
use. Not only is this necessary for accounting and audit
purposes but it is also necessary to avoid any unwanted
exposure of semen to the elements outside your tank.
Taking care of your tank will ensure the quality of semen
straws and allow you to breed for elite type and production
to enhance your herd! 
Telephone: (614) 873-4683
Fax: (614) 873-5751
www.selectsires.com
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