What is involved in freezing semen?
To process semen for freezing, the raw semen is diluted with a standard skim-milk glucose based extender and centrifuged to concentrate the sperm cells and remove seminal plasma. Seminal plasma contains factors that can be both protective and harmful to sperm. Primarily it is advantageous to remove seminal plasma when freezing semen. In the past clinicians would remove all of the seminal plasma, however, current research suggests it is beneficial to retain some, because seminal plasma is known to moderate the inflammatory response of the uterus when presented with sperm cells. Following centrifugation the sperm are diluted into the freezing extender which has a complex formulation including sugars, salts, egg yolk, skim milk and a cryoprotectant, predominantly glycerol. The semen is loaded into straws and frozen in liquid nitrogen vapor. This can be accomplished by one of two methods; either by floating a rack of straws over liquid nitrogen in a Styrofoam box or by a specially designed
