Lipids and proteins make up the plasma membrane of the sperm. Phospholipids will undergo a transition phase from a liquid to gel-state when the sperm is cooled below 18 ᵒC (27). Increased membrane disruption, cell death, and increased membrane permeability are experienced during the transition phase when phospholipids are lost from the plasma membrane (28). Plasma membrane fluidity and stability during cryopreservation are affected by the ratio of cholesterol and phospholipids in the plasma membrane (29). Cholesterol is an important additive to reduce membrane damage that occurs at low temperatures, and to maintain the fluid state of the membrane during the cryopreservation process (27). When cholesterol is used as an additive it helps to eliminate the phase transition at higher temperatures and at lower temperatures reduce the temperature at which the phase transition occurs (30). During the cryopreservation process it is thought that membrane damage occurs because of membrane lipids reordering (17) which can increase membrane permeability (31). When sperm undergo cryopreservation the temperature is lowered, which causes the water to move out of the cell and dehydration to set in, which changes the intracellular potassium and sodium ratio, allowing for an influx of calcium (32). The influx
Lipids and proteins make up the plasma membrane of the sperm. Phospholipids will undergo a transition phase from a liquid to gel-state when the sperm is cooled below 18 ᵒC (27). Increased membrane disruption, cell death, and increased membrane permeability are experienced during the transition phase when phospholipids are lost from the plasma membrane (28). Plasma membrane fluidity and stability during cryopreservation are affected by the ratio of cholesterol and phospholipids in the plasma membrane (29). Cholesterol is an important additive to reduce membrane damage that occurs at low temperatures, and to maintain the fluid state of the membrane during the cryopreservation process (27). When cholesterol is used as an additive it helps to eliminate the phase transition at higher temperatures and at lower temperatures reduce the temperature at which the phase transition occurs (30). During the cryopreservation process it is thought that membrane damage occurs because of membrane lipids reordering (17) which can increase membrane permeability (31). When sperm undergo cryopreservation the temperature is lowered, which causes the water to move out of the cell and dehydration to set in, which changes the intracellular potassium and sodium ratio, allowing for an influx of calcium (32). The influx