Pregnancy Outcomes Following Artificial Insemination and Embryo Transfer in Dairy Cows-Expectations vs. Reality.

Bovine embryo transfer (ET) has been a consistently growing market worldwide with in vitro produced (IVP) embryos now far outnumbering those produced by traditional superovulation. Because transfer of a viable blastocyst-stage embryo to the uterus bypasses many of the potential biological causes of early pregnancy failure associated with artificial insemination (AI; anovulation, sperm transport, fertilization failure, early embryonic death), pregnancy success should logically be higher following ET than following AI. However, this is not always the case. One of the main factors contributing to this paradox is pregnancy loss following ET, particularly with IVP embryos. This greater embryo mortality presents a significant obstacle to more widespread use of IVP embryos. Improvements in embryo culture media as well as in our understanding of the underlying physiological and molecular regulation of early embryo development and embryo-maternal communication leading to a successful pregnancy will significantly contribute to improved reproductive efficiency and sustainability in agri-food production.