Written by Dr Fiona Lacey

Embryo transfer (ET) involves the removal of an embryo (early developing pregnancy) from the uterus of one mare and the transfer of that embryo into the uterus of another mare. In recent years, the use of embryo transfer in many breeds is gradually increasing as confidence in both the technique and the reliability of the procedure grows.

The applications of embryo transfer in horses include :
  • 1. Obtaining foals from young performance mares tso they can continue to compete.
  • 2. Obtaining foals from mares that can no longer carry a foal to term.
  • 3. Obtaining foals from mares with non-reproductive health problems.
  • 4. Obtaining foals from mares whose owners are not prepared to risk them foaling down themselves.
  • 5. Obtaining multiple foals from the same mare, possibly by different sires.

Embryo collection usually occurs at day 7 or 9 post ovulation. Mares must be intensively managed to ensure correct timing of all procedures. The process of embryo collection involves a uterine lavage in which a sterile catheter is placed through the cervix into the uterus. The uterus is then filled with up to 4L of sterile embryo flush solution which is then allowed to flow back out through the catheter and through an embryo filter. Contents of the filter are then examined under a microscope for the presence of an embryo. If an embryo is recovered, it is then transferred through the cervix into the uterus of a suitable recipient mare. A significant amount of work is required to ensure that recipient mares are at a suitable stage of their cycle and ready to receive the embryo.

Selecting a fertile donor mare is paramount to achieving maximal success rates in an embryo transfer program. The best embryo donors are mature, reproductively sound mares or young healthy maidens.  Research has shown that embryos produced by aged, subfertile mares are inherently defective and have low survival rates after transfer to recipient mares. Therefore, old, subfertile mares are not optimal candidates for embryo transfer, however, with hard work acceptable rates can be achieved.

Not surprisingly, semen type also influences the rate of embryo recovery, with higher recovery rates for mares bred with fresh or chilled semen. Typically in a young, fertile mare using good quality semen, we can expect an embryo recovery rate of approximately 80% and a transfer success rate of approximately 90%. These figures can vary tremendously if older or sub-fertile mares are used but give an indication of what you should expect.

While embryo transfer is quite expensive to conduct due to the amount of work and level of expertise required, it is quickly becoming a widely used technique amongst many mare owners. We are seeing many people take advantage of our 'fixed price' offer as it gives them confidence knowing that if we don't achieve a pregnancy they won't be thousands of dollars out of pocket. For more details on our pricing system or if you are interested in learning more about successfully breeding an ET foal, please contact Olive Grove Equine Clinic on 9571 3992 or email info@ogec.com.au.