<i>Rhodiola sachalinensis</i> Polysaccharides as a Novel Cryoprotectant Improves Yak Frozen–Thawed Sperm Quality and Fertilisation Potential

Rhodiola sachalinensis polysaccharides (RSP), known for their antioxidant qualities, can scavenge superoxide anion radicals and prevent lipid peroxidation. This study aimed to determine the ideal extra concentration to use as a freezing extender additive and to explore the effects of RSP on the quality parameters and fertility ability of yak semen after cryopreservation. A commercial extender supplemented with varying concentrations of RSP (0, 0.02, 0.04, 0.06, 0.08, 0.1 g/L) was used to dilute the pooled semen samples from six yaks (four experimental replicates). The sperm's total motility, progressive motility, kinematics, membrane integrity, acrosome integrity, superoxide dismutase (SOD) activity, total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px) activity, catalase (CAT) activity, malondialdehyde (MDA), mitochondrial membrane potential (MMP), reactive oxygen species (ROS) and ATP levels were among the many parameters that were assessed after semen thawing. Our findings revealed that the total motility, progressive motility, kinematics, T-AOC, SOD, CAT, GSH-Px, MMP and ATP were significantly increased in the 0.06 g/L RSP-treated group than that of the control group (p < 0.05), whereas further increasing the concentration resulted in negative effects. Additionally, the MDA and ROS levels in 0.06 g/L RSP-treated group were notably lower than counterparts (p < 0.05). Following thawing, the fertilisation efficiency and subsequent developmental capacity of the 0.06 g/L RSP-treated group were considerably higher than those of the other groups (p < 0.05). Taken together, the inclusion of 0.06 g/L RSP in the semen freezing extender for semen cryopreservation is an effective strategy to enhance the quality and potential for fertilisation of yak spermatozoa. This study provides valuable insights into the role of RSP in ameliorating oxidative stress and preserving sperm function during cryopreservation.