The Equine Embryo Advances in Techniques: Trophectoderm Biopsy and Embryo Vitrification

Introduction
The commercial availability of equine embryo transfer has recently led to tremendous growth in breeder’s requests for desired genotypic and phenotypic specificity of offspring as well as embryo cryopreservation. These scientific advances come at a most opportune time for the horse industry because producing desired offspring not only reduces the “unwanted horse” population, but it favors a decrease of inherited disease, as well as permits the preservation of desired embryos until an owner can provide an optimal environment for their development.

Trophectoderm biopsy and preimplantation genetic diagnosis
Accurate gender identification of the equine fetus can be readily accomplished by transrectal ultrasonographic examination after 60 days of gestation. If the gender is not acceptable to an owner, the mare is often given an abortifacient agent and the unwanted fetus is aborted. While some consider abortion at this stage of gestation based on gender to be unethical, it should also be recognized that the practice is reproductively inefficient as well. Not only are pregnant recipient mares in use for at least 60 days carrying a fetus of unknown gender, but if aborted, they may fail to cycle again during the breeding season due to endometrial cup formation and the continued secretion of equine chorionic gonadotropin (eCG). Furthermore, the semen used to produce these pregnancies is wasted-it may be in limited supply, whereby the breeding dose for one mare precludes the use in another, or very valuable, as is often the case with frozen semen. Furthermore, stallion owners may not be aware of or in agreement with the abortion of their stallion’s offspring due to gender preference.