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Equine Embryo Transfer 1

Science fiction becoming reality

Embryo transfer in horses is a technique that is becoming increasingly available and widely used and in some breeds and disciplines is now considered routine.

The process involves using a surrogate or recipient mare to carry and raise a foal that was removed from the donor mare as an embryo only a few days old.


The technique of embryo transfer has several advantages :-

  1. It allows offspring to be born to performance mares without a break in work / training.
  2. It can make it possible for foals to be born to mares that for whatever reason would be unlikely to have a healthy pregnancy.
  3. Embryo transfer can be used to have an increased number of foals born from a genetically superior mare.

Surrogacy can also be a useful existence for unsound or unworkable mares that it may otherwise not be economically viable to keep.


When assessing a mare’s suitability as an embryo recipient or surrogate the following must be considered: The ideal surrogate is young and healthy, ideally between 4-10 years old and a proven breeder. It is also important to use a surrogate that it the same size or larger than the donor mare and of a temperament that allows repeated veterinary examinations with minimal stress.


A vital part of the procedure of embryo transfer is synchronising the reproductive cycle of the donor and recipient mares so that the prospective surrogate ovulates at the same time or up to 4 days after the donor mare. This part of the programme will require several ultrasound scans of the ovaries and uterus of both mares and often the use of drugs that manipulate the season. If possible, it is useful to have several possible surrogates lined up so that the timing of ovulation can be optimal and also occasionally because more than one embryo is collected from the donor.

Management Of The Donor

The donor mare can be covered naturally or artificially inseminated. The date of ovulation is noted as day 0.

Embryos are collected between days 6 and 9 post-ovulation. At this early stage it is not possible to tell if a pregnancy has occurred before attempting to recover any embryos before “flushing” the donor. Between 1-3 litres of a specially formulated solution is flushed into the uterus and out through a filter which is designed to collect the embryo(s). The filtered solution is examined closely under a microscope to hopefully identify an embryo. At this stage the embryo is just visible to the naked eye as a small “air bubble” that sinks.

The embryo is then introduced to the surrogate mare using a special catheter which passes through the cervix using a technique similar to that used for artificial insemination.

Success Rates

Embryo recovery rates average 75% and approximately 75% of embryos introduced into the surrogate will implant successfully as a healthy pregnancy which can be seen by ultrasound scan 1 week later.
Stringer Equine Veterinary Practice offers an embryo transfer package – for more information please contact us.

Richard Stringer BVSc MRCVS of Stringer Equine Veterinary Practice