Cryopreservation of in vitro-produced bovine embryos by vitrification: In pursuit of a simplified, standardized procedure that improves pregnancy rates to promote cattle industry use

The goal of cryopreservation is to retain the original stage of gametes and embryos after they have endured cooling and warming. Slow freezing is a standard method for in vivo-derived bovine embryo cryopreservation, three fifths of such embryos being frozen by this method globally. However, it is evident that slow freezing is not efficient for cryopreserving in vitro-produced bovine embryos. Hence, only one-third of in vitro-produced bovine embryos are cryopreserved. Vitrification is a preferred method for storage of human embryos; consequently, it has been explored as a novel means to store in vitro-produced bovine embryos, for which it shows considerable promise as an alternative to slow freezing. This is due to several reasons: vitrification is often less time-consuming than slow freezing; it does not need expensive slow rate freezing machines; and it has been proven to have comparatively higher survival rates. Yet, in the cattle industry vitrification continues to present shortcomings, such as possible toxicity of vitrification solutions and failure to standardize methods, which pose a challenge for its application to in vitro-produced bovine embryos. Therefore, determining the most suitable procedure is crucial to make vitrification more practical in commercial settings.