Vitrification of in vitro -derived bovine embryos: Targeting enhancement of quality by refining technology and standardising procedures

Bovine in vitro fertilisation technology has been widely exploited in commercial settings. The majority of in vitro-derived cattle embryos are transferred into recipient cows as recently collected (i.e. 'fresh') embryos due to the lack of a reliable cryopreservation method that results in favourable pregnancy rates following transfer of thawed embryos. This is a primary reason for the poor industry uptake of this extreme temperature freezing process. Numerous investigations into vitrification have revealed the importance of rapid cooling and warming rates, enhancing embryo viability after cryopreservation compared with conventional slow freezing. Those studies spawned a considerable assortment of cryovessels and diversity of procedures, delivering variable rates of success, which makes performing vitrification consistently a practical challenge. Hence, further research is required in order to both optimise and standardise vitrification methodology and to design a cryovessel that enables direct transfer of vitrified embryos to recipients after warming. In parallel with improvements in vitrification, it is important to continue to raise the quality of in vitro-derived cattle embryos through modifications in laboratory culture techniques. The twin goals of methodology refinement and standardisation, leading to embryo quality enhancement, are each imperative if in vitro fertilisation technology is to be adopted in the field. © 2019 CSIRO.