The 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

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.

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.

Proper removal of semen straws from inside of a semen tank.

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 been given to the neck design

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 or LN2 vapors can cause a freezing injury similar to a burn.

THE CARE AND MAINTENANCE OF SEMEN TANKS

Cutout of a semen tank, viewing the inner shell.

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• 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.

FILLING A SEMEN TANK1. 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.

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.

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.

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.

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 materi-als that could create microscopic holes in the tank.

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.

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) 873-4683Fax: (614) 873-5751www.selectsires.com

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THE CARE AND MAINTENANCE OF SEMEN TANKS

Frost forming on the neck of a tank, a sign of a slow vacuum leak.