Storage temperature of boar semen and its relationship to changes in sperm plasma membrane integrity, mitochondrial membrane potential, and oxidoreductive capability

The aim of this study was to analyze changes in sperm plasma membrane integrity, mitochondrial activity, and extracellular environment during storage of boar semen at 5 °C, 16 °C, and 25 °C for 10 days. Progressive sperm motility, plasma membrane integrity (SYBR-14/PI-test and HOS test), aspartate aminotransferase (AAT), and mitochondrial activity (JC-1-test and NADH-dependent NBT assay), as well as pH and osmolality were assessed in nine ejaculates of Polish Landrace boars. The plasma membrane integrity of the semen stored at 5 °C was similar to that of the semen stored at 16 °C and 25 °C; however, an increase in AAT activity of the semen stored at 5 °C revealed sperm membrane disorders as early as day 2. Significant differences in the progressive motility of the semen stored at 5 °C and 16 °C were observed at each of the evaluation times. This reduced motility was consistent with decreased sperm mitochondrial transmembrane potential and oxidoreductive capability. We inferred that the cooling of boar semen to 5 °C increases the permeability of the sperm plasma membrane, which may not be revealed by SYBR-14/PI staining or HOS testing. The loss of boar sperm motility that occurs during hypothermic liquid preservation may be connected with alterations in the plasma membrane stability and disorders of mitochondrial transmembrane potential and oxidoreductive capability.