Embryo transfer: past, present, future - a personal perspective.

Embryo transfer is just one of a range of assisted reproductive technologies - often the last one in a sequence of others - that has revolutionised the cattle breeding industry. The number of in vitro-produced embryos transferred annually now surpasses the number derived by traditional superovulation by a factor of four. Although issues with cryotolerance of IVP embryos, embryo loss, and, in some cases, calf birth weight remain to be fully resolved, IVP embryos are likely here to stay as a tool for genetic improvement in dairy herds, offering increased flexibility in sire usage allowing multiple pregnancies from elite dam-bull combinations to be generated and the ability to produce more embryos per unit time than traditional superovulation. What follows is a short personal look back at the last 30 years; if you are looking for deep insights into the underlying biology regulating embryo development, this is not the place to look! Please refer to some of the excellent recent reviews and research papers cited herein.