In Vitro Production of Equine Embryos

The development of methods to produce embryos in vitro in the horse has been delayed compared with other domestic species. Oocytes can be collected from excised ovaries or from the small or preovulatory follicles of live mares. Intracytoplasmic sperm injection is the only reliable method to fertilize equine oocytes in vitro. Intracytoplasmic sperm injection-produced embryos can be transferred into the oviducts of recipient mares or cultured to the morula or blastocyst stage of development for nonsurgical embryo transfers into recipientsʹ uteri. Embryos cultured in vitro have some morphological differences compared with embryos collected from the maresʹ uteri. Most notably, the embryonic capsule does not form in culture, and the zona pellucida fails to expand completely. However, embryo produced in vitro can result in viable pregnancies and healthy offspring.