Achieving success in conventional equine embryo transfer: A practical review

Equine embryo transfer is a well-established procedure in horse breeding programs and it's used to increase the number of offspring from valuable mares, obtain embryos from mares in competition and produce foals from mares unable to carry a pregnancy to term. The success of embryo recovery depends mainly on the day of flushing, management of insemination, and the fertility of donor mare and stallion. Other relevant factors include donor age and reproductive status, number of ovulations, operator experience, and flushing technique. Pregnancy rates after transfer are influenced by donor-recipient synchrony, the recipient's day post ovulation, embryo quality and developmental stage. The transfer technique and the characteristics of the recipient mare are also essential for pregnancy establishment and maintenance. This review evaluates the current status of equine embryo transfer and examines the principal factors affecting its outcome in order to maximise the efficiency of conventional embryo transfer programs.