Cryopreservation of Domestic and Wild Animal Spermatozoa: Update of Knowledge

Current sperm cryopreservation protocols for domestic and wild mammals aim to minimize the cryogenic damage caused by cell dehydration, ice formation, and osmotic stress. The optimization of sperm cryopreservation include the use of different synthetic and nonsynthetic-based extenders supplemented with additives (e.g., egg yolk, coconut water, etc.) and antioxidants (e.g., melatonin, L-carnitine, caffeine, resveratrol, etc.) that protect the plasmalemma, acrosome, and mitochondria against the detrimental effects caused by the cryopreservation process. Furthermore, the use of penetrating (e.g., glycerol, ethylene glycol, dimethylformamide, etc.) and nonpenetrating (e.g., sucrose and trehalose) cryoprotectant agents (CPAs) or their combination should be investigated to protect sperm during the freezing process in slow and ultra-rapid freezing procedures. Finally, new cryopreservation protocols should focus on freezing curves and initial cooling rates that allow optimal dehydration during freezing and adequate hydration during thawing. The suitable interaction of all these factors will allow a sperm subpopulation to survive cryopreservation with integrity and fertilizing capacity, contributing to the improvement of the efficiency of genetic resource management and the development of germplasm banks that support the preservation of genetic diversity in domestic and wild animals.