Addition of Casein to the Diluents during Semen Transportation Improves the Post-Thaw Qualities of Okinawan Native Agu Pig Spermatozoa

Abstract

This study was conducted to elucidate the protective effect of casein added to the semen diluents on reductions in sperm cryotolerance caused by seminal plasma (SP) proteins during semen transportation of Okinawan native Agu pig. Semen samples from three Agu pigs were immediately diluted with equal volumes of Beltsville thawing solution (BTS) containing casein sodium at a final concentration of 0.5%, and were transported within 1.5-2 h at 30˚C. Casein treatment during semen transportation had the beneficial effects on post-thaw sperm motility and plasmalemma integrity. Higher levels of cholesterol were retained in fresh sperm treated with casein than in untreated sperm in all pigs (P<0.05). The potential resistance to cell damage from cryoinjury was enhanced in sperm treated with casein during semen transportation in all pigs: caspase activity was markedly lower, and DNA integrity and intracellular ATP content were higher than those in untreated sperm treated. Furthermore, higher sperm penetrability to matured oocytes in vitro was maintained in post-thaw sperm treated with casein. These findings demonstrate that the addition of 0.5% casein to BTS during semen transportation improved the post-thaw qualities of Agu sperm by protecting sperm cryotolerance from the detrimental action of SP proteins prior to the freezing procedure.