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There are presently several techniques employed by commercial and academic laboratories worldwide. Select Breeders Service is equiped to utilize any of these various techniques in customizing a freezing protocol most suitable for the individual stallion. There are many differences between the techniques, however, a few basic principles are common to all.
Following collection, the semen is diluted and centrifuged to remove seminal plasma, which can be detrimental to sperm during the freezing process. This process also concentrates the sperm so that a sufficient number of motile sperm can be included in a single insemination dose.
- After seminal plasma has been removed, the sperm pellet is re-suspended in an extender which contains ingredients to protect the fragile sperm during the freezing and thawing process. These ingredients differ among extenders but usually include sugars, buffers against pH changes, egg yolk or milk proteins and lipids, the cryoprotective agent glycerol, and antibiotics.
- Sperm are allowed to equilibrate in the extender until they are loaded into plastic straws. These straws are clearly labeled with the stallion's name and registration number, as well as the date the semen was processed.
- The rate at which the extended semen is cooled from room temperature to -196° C is variable and dependent upon the specific procedure that is selected. This may be a relatively constant or highly variable progression through the cooling curve. Multiple step cooling is accomplished with a programmable cell freezing machine which pumps liquid nitrogen into the freezing chamber at a rate controlled by the pre-programmed computer.
- The frozen semen is then immersed and maintained in liquid nitrogen in special cryogenic containers. Select Breeders Service, Northgermany is equipped with an extensive, well maintained storage facility which provides the stallion owner with a safe, affordable method of maintaining and distributing the inventory of frozen semen.