In certain cases, mares can have specific fertility problems that can not be overcome using traditional embryo transfer. Problems such as an inability to ovulate, occluded oviducts or a malfunction in normal uterine immunity cause mares to be unsuitable for embryo transfer.

These mares are not without options. Oocyte transfer is a procedure in which the donor mare’s oocyte is aspirated and transferred into the oviduct of a recipient mare. The recipient mare is then bred to the desired stallion and fertilization of the donor mare’s egg occurs within the oviduct of the recipient mare. The resulting embryo is then carried to term by the recipient mare.