Morphology and biochemistry of in-vitro produced bovine embryos: implications for their cryopreservation.

Examination of some ultrastructural and physiological characteristics of in-vitro produced bovine embryos may help to explain why such embryos are more sensitive to freezing than their in-vivo derived counterparts. Improvement of embryo survival after freezing can be achieved by changing the conditions of their culture, selection of embryos based on the kinetics of their development, and changing "standard' freezing procedures. Cryopreservation of embryos by vitrification, in particular, seems to yield higher survival than conventional slow freezing. Further development of protocols requires additional embryo transfer studies to ensure that the ability of thawed embryos to develop normally in vivo correlates strongly with in-vitro survival assays.