PERSPECTIVE: Progressive techniques for wild mammal oocyte cryopreservation and recovery

The loss of wild biodiversity has encouraged the development of assisted reproduction techniques, such as in vitro fertilization, intracytoplasmic sperm injection and somatic cell nuclear transfer. The recovery and cryopreservation of oocytes derived from antral follicles are important steps to ensure the efficiency of these techniques. The capability of embryonic development depends on the success of these steps, especially for wild mammals, whose availability is limited, and accessibility is low. In general, it is possible to obtain from a few units to dozens of oocytes depending on the species and collection technique used. The cryopreservation protocols for domestic species are used as a starting point for studies on phylogenetically close wild species; however, the results are modest. Studies show viability after thawing ranging from 37‐70% and metaphase II does not exceed 42%. Currently, the main goal is to optimize these results by improving or comparing different cryopreservation and recovery methods. The susceptibility of oocytes to injury during cryopreservation shows inter‐specific differences. Optimal methods differ even between species that belong to the same phylogenetic group. Moreover, vitrification has been a promising technique for establishing biobanks. Protocols for evaluating the efficiency of these processes have been studied in several species. Therefore, this review discusses the use and development status of oocyte recovery and cryopreservation techniques in wild mammals and evaluates the success and perspectives of conservation of immature or matured oocytes in different species. The factors that impact successful oocyte cryopreservation must be established for each species.