Semen extender is a liquid diluent which is added to semen to preserve its fertilizing ability. It acts as a buffer to protect the sperm cells from their own toxic byproducts, and it protects the sperm cells from cold shock and osmotic shock during the chilling and shipping process (the sperm is chilled to reduce metabolism and allow it to live longer). The extender allows the semen to be shipped to the female, rather than requiring the male and female to be near to each other.Special freezing extender use also allows cryogenic preservation of sperm (“frozen semen”), which may be transported for use, or used on-site at a later date.
Semen extenders should not be confused with drugs or nutritional supplements designed to increase the volume of semen released during an ejaculation. The efficacy and utility of such products is dubious.
The addition of extender to semen protects the sperm against possible damage by toxic seminal plasma, as well as providing nutrients and cooling buffers if the semen is to be cooled. In the case of freezing extenders, one or more penetrating cryoprotectants will be added. Typical cryoprotectants include glycerol, DMSO and dimethylformamide. Egg yolk, which has cryoprotective properties, is also a common component.
Antibiotics are almost universal in semen extenders, especially those being used for shipping or freezing semen. Ticarcillin (often used in combination with clavulanic acid under the designation timentin), amikacin sulfate, penicillin, and gentamicin are commonly used.