Sperm cryopreservation in small ruminant is an efficient strategy to distribute spermatozoa for reproductive programmes, but this process reduces the fertility potential of frozen–thawed spermatozoa. The aim of the current research was to evaluate the impact of different concentrations of cysteamine (CYS) in soybean lecithin (SL)-based medium on postthawed buck semen quality and fertility potential. Semen samples were collected from five bucks, twice a week, then diluted in the SL-based extender containing different concentrations of CYS as follows: extender containing 0 mM (control, C0), 1 mM (C1), 2 mM (C2), 4 mM (C4) and 8 mM (C8) CYS. Motility characteristics, membrane integrity, abnormal morphology, mitochondrial activity, acrosome integrity, viability, apoptotic-like changes, lipid peroxidation, DNA fragmentation, ROS concentration, pregnancy rate and kidding rate were evaluated after freeze–thaw process. In results, C1 resulted in greater (p ≤ 0.05) total motility, progressive motility, average path velocity, membrane integrity, mitochondrial activity, acrosome integrity, viability, pregnancy rate and kidding rate compared to the other groups. Furthermore, supplementation of freezing medium with 1 mM of CYS presented lower (p ≤ 0.05) apoptotic-like changes, lipid peroxidation, DNA fragmentation and ROS concentration compared to the other groups. On the other hand, C8 presented the least (p ≤ 0.05) total motility, progressive motility, average path velocity, membrane integrity, mitochondrial activity, acrosome integrity and viability as well as the highest (p ≤ 0.05) apoptotic-like changes, lipid peroxidation, DNA fragmentation and ROS concentration compared to the other groups. Therefore, supplementation of freezing medium with 1 mM CYS could be a helpful strategy to protect buck's spermatozoa quality and fertility potential during cryopreservation process.
