Frozen Boar Semen Can Be Successfully Stored at -80°C, Reducing Need for LN₂ Storage Containers

This study explores alternative freezing approaches aimed at reducing or avoiding the use of liquid nitrogen (LN₂) to store boar semen. Sperm-rich fractions from three boars were pooled and frozen in 0.25- and 0.5-mL straws using four different protocols: a conventional method (Control; LN₂ vapours followed by immersion and storage in LN₂), FT1 (as Control but stored at -80°C), FT2 (LN₂ vapours followed by storage at -80°C), and FT3 (direct transfer from 5°C to -80°C plus storage at this temperature). Sperm quality and intracellular H₂O₂ production were evaluated at 30- and 150-min after thawing. Sperm motility and viability in FT1 and FT2 were similar to Control, whereas FT3 showed poorer sperm quality and higher intracellular H₂O₂ generation. Straw size also influenced cryosurvival, being lowest in 0.5 mL straws. In addition, sperm quality deteriorated alongside post-thaw incubation time. In contrast, storage time (one week vs. one month) did not show a clear effect on the evaluated parameters. In conclusion, these findings suggest that freezing protocols based on LN₂ vapour cooling, combined with storage at -80°C, could be a practical alternative for short-term storage of boar semen, reducing LN₂ use.