Frozen-thawed (FT) boar semen for artificial insemination (AI) in commercial pig production is still only used in exceptional cases, mostly to improve the genetic progress. This semen has not been used under production conditions as efficiently as liquid-preserved semen, because of the high susceptibility of boar spermatozoa to damage during cryopreservation and a complicated process of deep freezing. The processes of cooling, freezing, and thawing produce physical and chemical stress on the sperm membrane