Investigation of hydrostatic pressure-induced stress preconditioning of boar semen using modified cryopreservation

The aim of this study was to investigate the effect of varying hydrostatic pressure treatments (HP) on the boar semen quality during the modified cryopreservation. In Experiment I, combinations of pressure level (20/40/80 MPa) and duration of application (40/80/120 min) were used. Before freezing, only the magnitude but not the duration influenced the total (TM%) and progressive motilities (PM%). The 20/40 MPa levels yielded a significant (p < 0.05) improvement compared to control samples (atmospheric), but the 80 MPa was detrimental. The post-freezing-thawing (FT) motilities were influenced significantly by both the HP level and its duration. For TM%, the 40 MPa:120 min gave the highest post-FT result (54.8% ± 3.3%); however, the 40 MPa:80 min (41.0% ± 3.1%) application showed the largest and significant improvement (18.4% ± 3.1%) compared to its control (22.6% ± 3.1%) and compared to the improvement (12.9% ± 3.6%) achieved by 40 MPa:120 min. For PM%, the improvement with the 40 MPa:120 min application was slightly larger than with the 40 MPa:80 min one (15.2% ± 4.2% vs. 13.8% ± 3.3%); furthermore, the difference was not significant. In Experiment II, the 40 MPa:80 min combination was tested at four different stages of the semen handling. By pressurization after dilution with the freezing extender without glycerol, significantly higher post-FT values (TM%, intact acrosome% and head membrane%) were obtained. The two experiments demonstrated possible improvement in post-FT semen quality achievable through the appropriate application of HP to boar semen during cryopreservation.