Final answer:
Semen should be mixed with a protective extender, cooled, and frozen in nitrogen vapor before storage at -196°C. Before collection, the donor should be well-nourished and abstinent for a few days. Thawing involves careful warming to preserve sperm vitality.
Step-by-step explanation:
For storing semen specimens, it is necessary to provide nutrients such as glucose or fructose, a protectant such as egg yolk or milk to prevent cold shock, and a buffer to maintain pH balance, often using substances like Tris-hydroxymethyl-aminomethane. The semen-extender mixture should cool gradually to 5°C, remain at this temperature for several hours to equilibrate, then be packed into polyvinyl chloride straws before being frozen in nitrogen vapor at a controlled rate. This process involves freezing the semen to -150°C and then storing in vacuum sealed liquid nitrogen refrigerators at -196°C.
Before collection, individuals should be well-nourished and have abstained from sexual activity for a few days to ensure high quality semen which is viscous and cream-white in appearance. Collected semen is assessed for quality; it should have 70-80% motility.
Cryopreservation of semen involves freezing the semen for future use, and in vitro fertilization employs a swim-up technique using a culture media to separate the most viable spermatozoa. When required, frozen semen is thawed carefully in ice water and then warmed to body temperature, ensuring the vitality of the sperm is not compromised by the temperature change.