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Published online by Cambridge University Press: 27 February 2018
A number of methods can now be used to store the female germ plasm from farm species. New assisted reproductive techniques such as ultrasound guided oocyte pickup, followed by the in vitro maturation of oocytes together with cryopreservation enable the collection and storage of germinal vesicle or metaphase II secondary oocytes and more practically embryos after in vitro fertilisation. Following freezing using equilibration or vitrification protocols, oocytes and embryos can be stored at liquid nitrogen temperatures for as long as required. Despite much research interest, the efficiency of secondary oocyte freezing is low and the developmental potential of stored oocytes is directly affected by the local cellular and hormonal environment during maturation, fertilisation and extended culture in vitro. An alternative strategy which avoids many of the technical difficulties associated with mature oocyte freezing may be to cryopreserve primordial oocytes in situ within ovarian cortex. This approach has the added advantage that it may also provide a means of conserving the oocytes of rare species and it can be used to bank cells obtained from postmortem tissue samples or species for which IVF protocols may not have been fully optimised. Although the methodology is still in its infancy, when ovarian cryopreservation is combined with autografting, xenografting, or follicle culture, ovarian tissue freezing has the potential to restore or extend the fertility of domestic animals so maximising their genetic potential.