The researchers studied different methods for freezing boar semen to improve its viability and fertility. They tested various extenders, additives, thawing techniques, and protocols. The best results were seen with extender number Ⅳ, which increased sperm motility, viability, and integrity of the acrosome and plasma membrane. Adding O.E.P. to the extender further improved sperm quality. Pre-equilibration before freezing and thawing at 50℃ also enhanced sperm motility. Using thawing diluent number Ⅲ resulted in higher sperm motility compared to other diluents. Sows inseminated with the optimized frozen-thawed semen successfully got pregnant and had large litters.