Embryo Transfer
With the advancement of equine reproductive technology, embryo transfer
in mares is rapidly becoming a more popular and available technology. Why
would you want to transfer an embryo? There are many reasons people consider
embryo transfer that include: having multiple embryos/year from a valuable
mare, an older mare that you do not want to place through the stress of
pregnancy or foaling, a mare that usually conceives but has problems with
early embryonic death, or a show/competition mare that you don’t want to
give time off of the show seasons for foaling and raising a foal.
"What is involved in the process of embryo transfer?", you ask. The
embryo donor mare is bred like normal, except that it is imperative to know
exactly when she ovulates using palpation and ultrasound. The reason we must
know when the donor mare ovulates is so an embryo recipient mare is also
ovulating at approximately the same time. There are several embryo recipient
stations available in the U.S. to receive an embryo from you mare if they
have been given advance notice. It is also possible for you to have your own
recipient mare, but you generally need 4 - 5 recipients mares for one donor
mare. Your recipient mares also need to be palpated, ultrasounded, and
possibly chemically manipulated so that one of your recipient mares ovulates
at the same time as your donor mare.
After your donor mare has been bred and you have a recipient mare lined
up you wait for 6 to 8 days, depending on the circumstances, to harvest the
embryo. Harvesting an embryo is done by 1st flushing the donor mare’s uterus
with a special flushing fluid, running the fluids and (hopefully an embryo)
through a series of tubing and filters, and then searching for the embryo
under a microscope. Once an embryo has been found it can either be shipped
to the recipients mare using special solution and packaging, or placed into
a recipient mare at the clinic that ovulated at the same time as the donor
mare. Pregnancy diagnosis is performed on recipient mares at 7 to 14 days
after the embryo transfer.
There are several factors that affect both the rate of embryo recovery
from the donor mare as well as the acceptance of the embryo by the
recipient. These factors include the physical health of both mares, the
reproductive health of both mares, age of the mares, semen quality, handling
techniques of the semen and embryo, stress levels of the mares, hormone
levels of the mares, etc. All of these factors make predicting success rates
very difficult. There is published data that suggest embryo recovery rates
that vary from 50 to 90%. Success rates of embryo acceptance and pregnancy
confirmation in recipient mares vary from 20 to 60%.
As you can see embryo transfer does and will continually increase as
playing an important role in equine reproduction. There is a great deal of
work and technicality involved with transferring embryos, but this process
can also be rewarding by providing multiple foals or that special foal out
of your favorite older mare.
