Embryo Transfer (ET)

ET is the process where a 6-8 day old embryo is flushed from a donor mare and transferred into a recipient mare whose oestrous cycle has been synchronised with the donor, and this recipient mare carries the foal to term. The main advantage and most common use of ET is to obtain foals from performance mares without interrupting their sporting careers.

The process is reasonably straightforward, with the mare being bred as normal, and then returning to Chiltern Equine Clinic a week later for the day in order for the embryo flush to be performed. The flush is a reasonably non-invasive, non-painful procedure that takes place under light sedation. It doesn't have to interfere with the training program of the mare. The embryo is then transported by courier to Twemlowes Stud Farm to be transferred into a suitable recipient mare. The pregnancy can be diagnosed 5-7 days later to confirm that the recipient held the pregnancy.

Other reasons why ET is such a useful tool...

More than one foal can be produced from genetically valuable mares per season while limiting the risk to the mare.

Breeding multiple foals from individual mares per year.

Obtaining foals from mares with a reproductive problem.

Obtaining foals from mares with non-reproductive health problems.

Shortening the generation interval by breeding 2 and 3 year old fillies (a valuable use of sport horse fillies before they are ready for serious work).

Extending the reproductive life of an older mare.

Older mares are prone to reproductive aging with conditions including Peri-glandular fibrosis and Endometriosis often being diagnosed which can result in early embryonic death or abortion. They can often become pregnant but some are unable to carry their foal to term. These mares are classic candidates for ET.

In short, the donor mare has to be able to ovulate a viable oocyte and provide suitable conditions in the oviduct for fertilisation and maturation of the early embryo, and provide successful transportation into the uterus where an appropriate environment is necessary for a short period of time until the embryo is removed.

It is important to note that the embryo recovery rate will differ depending on the circumstance, for instance with young healthy mares (<14years) the recovery rate (RR) can average 70-90% compared with aged (>14years) mares, at 50-80% and particularly older maiden mares, where the RR can drop below 50%.

If the mare is sub-fertile to begin with, then a RR<60% may only be expected.

Fresh vs chilled vs frozen semen; the type and quality of semen can really affect the recovery rate.

In addition to this it is important to note that older mares also have an increased risk of producing embryos with DNA abnormalities resulting in a higher incidence of embryonic or foetal death.

Once you have decided that you would like to proceed with ET for your mare, it is important for us to carry out a general physical examination, reproductive examinations and take a breeding history record. We need you to outline your required goals, i.e. the number of embryos you would like, stallion choice and the amount of time we have to achieve this for you (considering time of year/work commitments of mare etc), so there is no risk of disappointment from having unachievable goals that can't be reached.

Chiltern Equine Clinic does not have a herd of recipient mares therefore all obtained embryos will be transported to Twemlowes Stud Farm for implantation.

Prices for 2024 Season coming soon!