Application of embryo transfer using in vitro produced embryos: intrinsic factors affecting efficiency.

Embryo transfer remains a viable approach to increase propagation of offspring from high genetic merit females. Although it is now over 60 years since the report of the birth of the first calf from embryo transfer, utilisation of embryo transfer technology worldwide is not widespread. Limitations of conventional procedures for superovulation and embryo transfer are not limited to but include variability in response to superovulation, the labour intensive nature of superovulation procedures, time required between collections and cost of technology. Recently, harvest of ova and transfer of in vitro produced embryos has received more attention as a potential alternative to conventional superovulation and subsequent embryo transfer. Aspiration of follicular ova and in vitro embryo production offers potential advantages in reducing loss of female germplasm occurring through the natural process of ovarian follicular atresia, can increase yield of embryos from elite donor cows beyond that possible with superovulation, and provides a means of salvaging genetic material from valuable animals at slaughter or those culled for disease control or other reasons. Recent evidence indicates poor ovum quality is a major factor limiting in vitro embryo production and discovery of a role for intrinsic factors such as ovum follistatin and cumulus cell cathepsins in control of ovum quality has led to ongoing research on new technologies to increase yield of transferable embryos.