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Dairy Pipeline: January 2003
Ray L. Nebel
Extension Dairy Scientist,
Reproductive Management
(540) 231-4432
email: rnebel@vt.edu
The primary objective in handling semen properly is to conserve the fertile life of sperm until deposition in the female. This is accomplished by minimizing exposure of semen to temperature fluctuations and contamination with other compounds especially water and soap. The semen storage tank is a large, metal, vacuum-sealed liquid nitrogen refrigerator encased within an extremely efficient insulation system. With proper attention and handling, most liquid nitrogen semen storage tanks give years of troublefree service, but all storage tanks will eventually fail. To ensure maximum holding time, the tank should be kept in a cool and dry location away from direct sunlight, in a clean and well-ventilated area away from drafts, elevated above concrete to prevent corrosion, and where it can be seen daily. Particular attention must be given to the neck and vacuum fitting. Accumulation of frost on these areas indicates that the vacuum insulation has been lost and liquid nitrogen has been evaporating rapidly. In addition to the obvious error of permitting a liquid nitrogen storage tank to go dry, stored semen may be exposed to adverse high temperatures when straws are being removed for thawing. An accurate inventory and location of the semen stored in the liquid nitrogen tank is important to prevent exposure of semen during searching for the straw prior to removal for thawing. Thermal injury to sperm is permanent and cannot be corrected by returning semen to the liquid nitrogen. For optimal maintenance of sperm viability, canisters and canes containing semen should be raised into the neck of the tank only for the time required to retrieve a single straw. The canister should not be raised above the frost line that appears in the neck of the tank and exposure to elevated temperatures should not exceed 5 to 8 seconds.