LED-based red light photostimulation improves short-term response of cooled boar semen exposed to thermal stress at 37°C

Pre-treatment of boar semen with a red light photostimulation procedure increases its "in vivo" fertilising ability. However, "in vitro" conducted studies shown contradictory results regarding the ability of photostimulated spermatozoa to react against strong stress and to achieve the capacitation status. The aim here was to determine the effect of photostimulation on the response to short-term moderate thermal stress of boar semen. Boar semen was exposed to red LED light regime emitting a 620-630 nm during 10 min of light, 10 min of rest and 10 min of light after 3 hr since semen was collected. An aliquot without photostimulation was included as a control. After the photostimulation, the sperm cells were incubated for 15 min at 37°C. Afterwards, motility, viability, intracellular Ca2+ level and production of reactive oxygen species (ROS) and peroxynitrite were analysed. The results showed that the photostimulated group maintained total motility throughout the time, whereas a significant decrease in total motility was observed in the nonphotostimulated control group. Furthermore, for kinetic parameters of motility, a significant increase was observed in LIN, STR and WOB in photostimulated spermatozoa. Peroxynitrite production was significantly increased in the photostimulated spermatozoa, whereas viability, ROS production and intracellular Ca2+ levels were not affected by photostimulation. In conclusion, photostimulation of commercial boar semen has a positive effect on motility of spermatozoa subjected to a short-term moderate thermal stress, which was concomitant with an increase in peroxynitrite production.