Many breeders are opting to handle and store their own frozen semen, both to avoid storage costs and for the convenience of having their semen close at hand. Handling and storing frozen semen is not difficult, but it must be done properly and safely. With the right equipment and practice, anyone can handle and store their own frozen semen.
- Frozen semen is packaged in straws labeled with the stallion‘s name, which are put into cup-like plastic cylinders called goblets, which are then snapped onto aluminum canes for storage. The canes have a label on top, where the stallion’s name is written in permanent marker (a fine point “Sharpie” marker works well for this). Straws, canes, and goblets are handled with straw tweezers. Protect fingers from nitrogen burns by wearing thin gloves.
- The first item one needs for storage of frozen semen is, of course, a storage tank. There are many makes and models of tanks, but all are essentially the same, being large cylinders of stainless steel or aluminum, with an inner vacuum lining somewhat like that of a thermos. There are from one to six storage canisters inside. A canister sits well down inside the tank, and is pulled up by a long handle which notches into a groove in the neck of the tank. A used storage tank can be purchased from representatives who service semen storage tanks for dairies and beef operations. A. I. supply companies and frozen semen brokers also sell used tanks. The main difference between an older, used tank and a new one is the hold-time, or the frequency with which the tank needs to be supplied with liquid nitrogen. A new tank can be topped-off every four months, while a used one will probably need to be serviced every two months. As long as a tank is not frosting up on its exterior after filling, it is a secure tank. All tanks should be checked weekly for signs of leakage and measuring of the nitrogen level. This is done by inserting a measuring device down the center of the tank. A tank should be kept about half full, and its level never allowed to drop below three inches.
Equipment and Supplies:
- Liquid nitrogen--available from welding and medical supply shops or from “door-to-door” suppliers
- Liquid nitrogen measure--available from suppliers or make your own--use wood, plastic or metal--no cylindrical measures
- Thin latex or cotton gloves--to protect fingers from nitrogen burns
- Long-sleeved shirt--to protect skin against accidental splashing of nitrogen
- Safety glasses--for eye protection
- Straw tweezers--plastic (may be best for beginners) or stainless, for handling the individual straws, goblets and canes
- Assistant--working between two tanks requires at least two people
- Fill the vessels slowly to minimize contraction and expansion stresses. Never seal the vessel tightly, as it is designed so that no internal pressure builds up. The stopper must not be too tight fitting, or the container may be damaged or burst. Never fill the container more full than the bottom of the neckline. When measuring nitrogen use metal, plastic or wood. Never use a tube, as the nitrogen may spurt up through the tube and splash out. Dispose of nitrogen on the ground, never on concrete or blacktop surfaces.
- Never clean with abrasive cleaners, use mild detergent and water and always wipe dry. Remember that the liquid nitrogen is evaporating constantly and must be replaced periodically. The evaporation rate will depend upon the use, age and condition of the vessel.
Handling the Container:
- Do not drop or tip the container. Do not slide, roll or walk the unit, because the vibration or shock can result in partial or total vacuum loss. If it’s too heavy to carry, use a roller base.
- One liter of liquid nitrogen produces 25 cubic feet of gas, displacing oxygen in the surrounding area. Always work in a well ventilated area. Call for medical help immediately in the event someone is seriously splashed by nitrogen, or becomes dizzy or loses consciousness after exposure to liquid nitrogen.
- The frozen semen will arrive in a shipping container, often a short hold-time container that will need to be promptly unloaded and returned to the semen broker. If you are unskilled at transferring frozen semen, try to work with a veterinarian or other skilled technician on your first attempt. Some shipping tanks will arrive with the straws already in goblets and on canes. These are relatively easy to transfer. Loose straws require more skill.
- No matter how your semen arrives, it is critical to remember that when frozen semen is exposed to thawing temperatures for more than three seconds, cellular damage may occur. Therefore, it is important to work quickly. If you have not completed the transfer in three seconds, dip the canister back down into the tank to re-chill it, and try again.
- If your straws of semen arrive loose in canister, you must first transfer them into goblets, and then snap the goblets onto canes for storage. Pre-chill the goblets and canes before use, and have them ready in a canister.
Steps to Transfer Semen:
- Arrange the tanks, and chairs for the handlers to sit on, in a well-lighted and ventilated area.
- Keep the canisters you are working with two inches below the neck of the tanks at all times, and dip them back down into the nitrogen every few seconds to keep them cold.
- With the canisters pulled up to two inches below the neck of the shipper, grasp a straw with your straw tweezers, identify it, remove it and transfer it into a chilled goblet. Immediately re-submerge the canisters.
- Next, have your assistant pull up a canister containing a chilled cane marked with the stallion’s name, snap the goblet onto it , and re-submerge. Some people combine these steps, by having the goblets attached to the canes before transferring the straws.
- Remember to take it step-by-step. First, the straws need to be identified. Next they are sorted into goblets. Finally, the goblets are snapped onto canes. Re-submerge every three seconds and/or between each step. Make sure all the equipment is pre-chilled. Soon you will be handling and transferring frozen semen like a pro!
- Timing is critical. Research has shown that cellular damage occurs when the semen is exposed to room temperatures for longer than three seconds. If the straws have not been successfully transferred within three seconds, they should be re-submerged in the tank to maintain their temperature.
- Work at least two inches below the neck of the tank at all times, as the temperature near the top of the neck can be several degrees warmer, and the risk of cellular damage exists.