Cryopreservation-induced oxidative damage in ram sperm and the role of natural antioxidants as cryopreserved sperm quality enhancers

Ram sperm cryopreservation is crucial for artificial insemination and genetic improvement programs in the small ruminant industry. Semen handling and cryopreservation can negatively affect sperm quality irrespective of the storage conditions and extenders used. Studies have reported an increase in reactive oxygen species in ram sperm during cryopreservation, leading to oxidative stress. Oxidative stress significantly compromises the sperm fertilising ability by inducing oxidative damage to protein, lipid, and nucleic acid components of the sperm cell. The supplementation of antioxidants to semen extenders before cryopreservation can minimise this detrimental effect. Natural antioxidants have emerged as an economical and effective source of additives to preserve and enhance ram sperm quality during semen preservation. This review presents an overview on harmful effects of oxidative stress on ram spermatozoa, extrinsic and intrinsic factors responsible for occurrence of oxidative stress, as well as natural antioxidants and their potential as an additive for sperm quality enhancers in different ram breeds. Taken together, we suggest that synergistic combinations of antioxidants that are economically feasible, such as resveratrol with vitamins C or E, could be the way forward, but warrant further investigations into dosage versus toxicity, standardised extraction protocols, and breed-specificity in their supplementation in semen extenders.