Semen extender is a liquid diluent which is added to semen to preserve its fertilizing ability. It acts as a buffer to protect sperm cells from their own toxic byproducts, as well as protecting the sperm from cold shock and osmotic shock during the chilling and shipping process (the semen is chilled to reduce metabolism). 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, 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 volume increasers is dubious.