Embryo transfer has proved to be a powerful technology in genetic improvement of farm animals, primarily to propagate the genes of females of superior pedigree. In cattle, particularly in the dairy industry, breeding programs have been developed to promote genetic progress by strategic use of elite females via multiple ovulation embryo transfer (MOET) programs. In addition to conventional methods to produce embryos available for transfer, new technologies that produce embryos after cloning by somatic cell transfer or transgenesis are available; however, they are not widely used commercially.
Embryo transfer protocols have also been extensively used in research, in areas such as fetal-maternal interactions, models of human and animal diseases, and production of transgenic animals to produce therapeutic proteins for humans. Except in horses, embryo transfer programs in most mammals include administration of drugs that stimulate a supraphysiological growth of follicles in the ovaries followed by hormonal induction of ovulation. This approach increases the chances that multiple embryos are collected per procedure.
Collectively, the hormonal protocol used in animals is known as superovulation, whereas in humans it is referred to as ovarian stimulation. In farm animal embryo transfer, transferable embryos are embryos deemed of acceptable quality for transfer into recipient animals as fresh embryos or to be cryopreserved for future use. In 2018, in cattle, the number of transferable in vivo-derived (IVD) embryos produced in the world was ~470,000—less than half of transferable embryos produced via in vitro fertilization procedures (just over one million embryos). According to the Data Retrieval Committee, a committee of the International Embryo Technology Society, the total production and number of cattle embryo transfers were greater for in vitro produced embryos than for IVD cattle embryos for the first time in 2017.
