Application of High Hydrostatic Pressure (HHP) to Improve Cryopreservation of Young Bull Semen

The objective of the study was to determine the effect of high hydrostatic pressure (HHP) on quality of cryopreserved semen of young bulls. Semen for this study was collected from 8 bulls aged between 13 and 18 months at monthly intervals, from June to September. After collection, semen was diluted in a commercial Bioxcell® extender (one part at 1:1 and a second part to give a sperm concentration of 20 million/0.2 mL), filled into straws and treated with HHP at 30 MPa for 90 min. After HHP treatment, pre-diluted semen (1:1) was diluted to a sperm concentration 20 million/0.2 mL and filled into straws. In addition, part of the semen diluted to a concentration of 20 million/0.2 mL was not treated with HHP (control). All of it was held at +4°C and frozen in a freezer after 2.5-h equilibration. Semen was thawed in a water bath at 38°C and subjected to estimation of the percentage of motile sperm both subjectively and using a computer-assisted semen analyzer and cytometric assessment of sperm cell membrane integrity. Subjective motility and fast progressive motility were significantly higher with pre-diluted (1:1) and HHP treated semen compared to control (P<0.05). No significant differences were observed in percentage of membraneintact spermatozoa between control and experimental groups. Additionally, the influence of HHP on the sperm of individual bulls was assessed. In bull number 2, the HHP treatment after semen pre-dilution significantly improved progressive motility from 54.1 to 63.4 percent (P<0.05). In bull number 4, the HHP treatment after semen pre-dilution significantly improved subjective motility, rapid motility and progressive motility by 12.5, 16.8 and 16.3 percent, respectively (P<0.05). No effect was seen for 6 bulls. It is concluded that for some bulls, the application of HHP before semen freezing may improve the cryopreservation outcome. However, this requires further research in this area, also to determine the fertilizing capacity of bull semen exposed to high hydrostatic pressure.

Cells under pressure: how sublethal hydrostatic pressure stress treatment increases gametes' and embryos' performance

The principal approach in in vitro embryo culture and manipulation has been a defensive one: procedures aim to satisfy passively the supposed or real physiological needs of gametes and embryos. Similarly, during cryopreservation the aim is to cause minimal damage to cells whilst attempting to obtain the highest achievable cell survival. However, carefully chosen and precisely controlled sublethal stress treatment of cells has been described to improve embryos’ and gametes’ performance, and, as a consequence, subsequent morphological survival, fertilisation, in vitro development, pregnancy and farrowing rates improved considerably compared with untreated controls. This review summarises studies that open up a new approach: instead of – and besides – trying to passively reduce the harm to cells during in vitro manipulations and culture, procedures may also prepare the cells themselves to ward off or reduce the damage by turning up the cells’ own, inner capacities.