Cryopreservation induced changes in avian sperm: Molecular and biochemical perspectives

Cryopreservation is a pivotal tool for avian semen preservation but imposes detrimental effects on sperm viability and fertility. This review explores the biochemical and molecular mechanisms underlying cryopreservation-induced injuries in avian sperm, particularly in chickens, turkeys, ducks, and geese. Avian sperm exhibit a unique composition, including high polyunsaturated fatty acids, diverse proteins, and limited seminal plasma, rendering them vulnerable to oxidative stress and membrane damage during freezing and thawing. Cryopreservation leads to oxidative imbalance, lipid peroxidation, DNA fragmentation, and changes in antioxidant enzyme activity. Membrane rafts lose sterols, altering membrane fluidity and triggering early apoptotic events. Epigenetic modifications, including altered DNA methylation and RNA methylation, further compromise sperm function. Proteomic and transcriptomic changes, including disruptions in energy metabolism and motility-related proteins, contribute to reduced fertility. This review organizes the evidence around a proposed interconnected cryoinjury cascade; osmotic and ice-crystal stress, membrane damage, mitochondrial dysfunction, oxidative stress, and DNA/epigenetic damage, converging on reduced fertility, and distinguishes findings demonstrated directly in birds from those extrapolated from mammalian models. Comparative data are presented across chicken, turkey, duck, and goose sperm where available, with gaps identified. More thorough evaluation of cryoinjuries and biomarkers for fertility prediction is made possible by developments in analytical techniques including flow cytometry, metabolomics, and proteomics. Techniques like sterol inclusion, antioxidant supplementation, and cryoprotectant optimization show promise in reducing cryoinjuries. A comprehensive understanding of these intricate biochemical mechanisms is essential for enhancing genetic conservation in avian sperms, improving reproductive efficiency and optimizing semen cryopreservation procedures. This review also discusses potential future developments in integrative omics, nanotechnology, and molecular breakthroughs to maximize cryopreservation efficacy.