Red LED Light Irradiation Increases the Resistance Against Environmental Stress of Frozen Bovine Sperm Thawed in Suboptimal Conditions

This work sought to test the positive effect of red LED light on frozen bovine sperm resistance to thawing in suboptimal conditions. Moreover, a preliminary study explores whether this improvement could have any repercussions on in vivo fertilizing ability. Thus, frozen bull semen straws (n = 16) were thawed (a) with irradiation for 5 min at 20 °C (2 min light, 1 min darkness, 2 min light; PHOTO); (b) without irradiation for 5 min at 20 °C (ET); or (c) through immersion into a water bath at 38 °C for 40 s as standard control (CONTROL). Sperm quality and preliminary, purely descriptive AI trials were performed. The PHOTO samples demonstrated significantly (<i>p</i> < 0.05) improved percentages of intact acrosomes, progressive motility, DNA condensation and fragmentation, and viable sperm with high ROS/superoxides. The viability of PHOTO samples decreased significantly (<i>p</i> < 0.05) when compared with the ET ones. Overall results of both the PHOTO and ET samples were poorer than those of the CONTROL. Otherwise, the PHOTO straws yielded greater pregnancy rates (64.0% vs. 49.4% in CONTROL) when evaluated at two different farms. The results suggest that irradiating cryopreserved bovine sperm during thawing in suboptimal conditions could improve AI pregnancy rates, although more in vivo studies are needed to support this conclusion.