The development of in vitro embryo production in the horse.

The development of techniques to produce equine embryos in vitro is reviewed with specific reference to intracytoplasmic sperm injection (ICSI). Unexplored 50 years ago, this technology has progressed rapidly in the last 20 years to become a commercial reality for the equine breeding industry. Improvements in our understanding of oocyte and embryo competence in the horse have been key factors in overcoming some of the initial problems associated with ICSI. It is now possible to obtain high nuclear maturation and cleavage rates in vitro and the most limiting factor, presently, is the low rate of development to the blastocyst stage. However, in spite of this, once obtained, these in vitro-derived blastocysts can result in pregnancy rates in excess of 60% following transfer.