Motility degradation rate, plasma membrane integrity, and kinematics during cryopreservation of boar (Sus scrofa domesticus) spermatozoa in different freezing extenders and thawing temperatures

Despite the very limited use of frozen-thawed semen (FTS) in pig artificial insemination, FTS in some instances can be truly beneficial as it is not constrained by time (shelf-life) and space (regional quarantine) restrictions unlike fresh-extended semen (FES). It also allows long-term banking of highly valuable genetics particularly during epidemics. This study compares existing and currently available freezing extenders used in boar semen cryopreservation aimed to optimize protocols useful for in-country local swine industry with special focus on the motility degradation rate (MDR), and plasma membrane structural (percent live) and functional (HOST reactive) integrity. Treatment samples from ten freezing runs using five different sperm-rich fractions were frozen using three different cooling/freezing extenders (CE/FE): A) LEYGE, B) BF5, and C) Cryoguard (~500 x 106 spz/mL) in liquid nitrogen (LN2) vapor, thawed either at ~38°C or ~50°C for 20 sec, and examined using the Sperm Class Analyzer® CASA system. LEYGE had significantly the highest MDR from about 50% reduction post-thawing to 70% one hour thereafter. Cryoguard consistently had the lowest MDR although closely similar to BF5. There was a minimal effect on the plasma membrane functional integrity and was primarily limited to LEYGE and BF5. A fertility trial is recommended to attest the performance of FTS vs FES in terms of conception rates and the litter size following post-cervical AI before full-scale production and potential adoption by the breeder swine industry.