Historical Aspects of Equine Embryo Transfer.

The research article focuses on the historical advances in equine embryo transfer, tracking the progression from its early stages in the 1970s to the present. It also explores the challenges that have persisted over the years, particularly regarding the low embryo recovery rates from donor mares.

Initial Progress of Equine Embryo Transfers

• The researchers discuss the history of equine embryo transfers, highlighting that early attempts were made simultaneously in Cambridge, England, and Kyoto, Japan in the 1970s. In these early stages, embryo transfers were often undertaken surgically.
• Initially, the process involved flushing the uterine horn ipsilateral to the side of ovulation. However, this method only achieved limited success due to the continued movement of the embryo throughout the uterine lumen after day 6.
• Upon the realization of the embryo’s continuous movement, the researchers decided to flush the whole uterus instead. This new approach led to an improvement in success rates.

Development of Non-surgical Methods and the Success of Inter-species Transfers

• Subsequent to the surgical methods, a non-surgical technique was developed. This procedure involved transferring the embryos via the cervix and proved to be increasingly successful.
• Using the non-surgical method, the success rates of equine embryo transfers have markedly increased over time, with current pregnancy rates between 75%-90%.
• Further developments have included the experimental use of embryo transfers in horses and donkeys, illustrating the unique ability of equids to carry interspecies hybrid conceptuses and extraspecies pregnancies to full term.
• This research also explored the potential of creating genetically identical twin foals by splitting day 4-8 cell embryos and day 6 compact morulae.

Persistent Challenges in Enhancing Embryo Recovery Rates

• Despite the significant advances in the field over the past 45 years, there remain persistent issues, particularly concerning the relatively low embryo recovery rates from donor mares treated with exogenous gonadotropins to stimulate superovulation.
• This challenge arises due to the toughness of the ovarian tunica albuginea, which forces ovulation through the ventrally situated ovulation fossa. Here, multiple follicles compete with each other and undergo luteinization before they can ovulate properly, leading to low recovery rates.