Effects of Time of Mild Oxidative Stress before Freezing on the Post-Thawed Sperm Quality

The purpose of this study was to consider the effect of mild oxidative stress period on the frozen-thawed bull semen performance. In this study، 120 minutes was considered for equilibration of sperm before freezing. One µm of Nitric Oxide (NO) at the 0، 45، 90 and 120 cooling period was added to the diluant before cryopreservation. Sperm motion parameters، plasma membrane integrity، acrosome integrity، viability، apoptosis and mitochondria activity were assessed. Induction of oxidative stress with nitric oxide in the T0 and T45 groups led to significant improvement of total (88. 4 ± 2. 8، 84. 7 ± 2. 7) and progressive motility (50. 4 ± 2. 5، 49. 5 ± 2. 5) when compared to other groups. Percentage of plasma membrane integrity and viability were not different in T0 (74. 4 ± 2. 9 and 85. 6 ± 2. 9) and T45 (75. 6 ± 2. 9 and 84. 6 ± 2. 3) groups، where as it was significantly higher when compared with T90 (63. 6 ± 2. 9 and 69. 6 ± 2. 3) and T120 (61. 5 ± 2. 9 and 54 ± 2. 3). Moreover، the highest significant percentage of spermatozoa with active mitochondria was observed in the T0 (82. 5 ± 3. 1) when compared with T45 (65. 7 ± 3. 1)، T90 (42 ± 3. 1) and T120 (43 ± 3. 1). Acrosome integrity and linearity of sperm were not affected by the oxidative stress treatment time. It seems that applying oxidative stress using 1 µM NO would improve post-thawed bull sperm quality at the T0 and T45 time of cooling.