Equine Embryo Transfer – What’s it all about?

What is embryo transfer?

Embryo transfer (ET) is taking embryos from high -class mares (the donor), putting them in low-class mares (the recipient), with the hope of getting high-class foals. Horses born by embryo transfer can compete in most sports except racing.

Have any ET foals made it in top class sport?,/strong>

Yes, in show jumping there are many, for example, Cornet Obolensky, Mylord Carthargo and Glocks London are famous embryo transfer products.

Is ET common?

In other farm animals, ET is common and more successful. This is because superovulation (inducing multiple ovulations by using hormones) is possible in these animals and the embryos are tougher due to their structure and they can survive freezing more easily.

In show jumping, about 3% of foals born in Europe are by ET, for example, about 800 ETs in France, 600 in Germany, 300 each in Holland and Belgium. However, less than 100 embryo transfers are performed in Ireland annually.

ET is most common in show jumping mares, however, recently it has becoming more popular in eventing, such as the dual Badminton and Burghley winner Headley Britannia.

Is the success rate of ET-produced horses similar to or better than non-transferred horses?

The success rate is only slightly better, ie about 6% of these horses become international class performers. 6% of the 3% of foals born in Europe is obviously a very small number, so the overall amount of international standard ET horses is small.

What mares are suitable to perform embryo transfer on? Embryo transfer can be performed on any mares that can become pregnant for a short time. Usually three-year-old horses are the youngest, while a 22-year-old mare is the oldest horse which I have taken an embryo from.

There are three main reasons clients may ask for this service:

1: A client may have a top-class mare who is too valuable to carry the risks of pregnancy (she’s too posh to push) and the client may want more than one foal a year from this mare.

2: A mare may be performing well in her sport and the owner wants to get a foal from her without her having to take maternity leave. She can continue her career and even be sold while producing a foal or two at the same time.

3: A mare may have a physical problem preventing her from carrying a live foal safely. This may be a reproductive tract problem or other physical problem such as laminitis.

Why should I consider embryo transfer for my mare?

Consider ET if your mare has reached a high standard in her sport or if she is the dam of such a horse.

Sisters and more distant relatives of good horses are possibly not valuable enough to get a return on your investment. However, some bloodlines consistently produce top performers, so young performing mares from these lines may be good candidates.

Of course, no mare is guaranteed to produce top performers (consider Ratina Z, European and Olympic champion, she has had over 25 foals and has only a couple of Grand Prix performers).

However, breeding from top-performing mares carries a much higher chance of getting a top performer or top stallion. We need these horses in our studbook and because we have so few of these quality mares, everything should be done to encourage their owners to increase their output, so to speak.

We have so few top performing mares here compared to other studbooks that we need to utilise ET more urgently to give us our best chance of producing top-level show jumpers and stallions once again.

What is the success rate of ET?

The statistics worldwide are 70% chance of getting an embryo on a flush and 70% chance of this embryo transferring successfully. This means a 50% chance of a successful pregnancy per flush.

There are a lot of variables here:

Will flushing the mare affect my competition mare’s performance after?

Probably not. ET is not seen by most to affect a mare’s subsequent performance. Similarly, if the mare is not given a break from work during her ET programme, some feel it may affect the embryo recovery rate.

What is involved?

What kind of recipient mare is needed? The recipient mare should be young (four to 10 years ideally), in good body condition (rising condition is better than too thin or too fat), large enough to carry a potentially large foal (greater than 15.2 hands should be fine if she is wide enough), and quiet enough to catch and handle.

Experience in foaling is not essential, but a reproductively sound mare is essential. Thoroughbred mares are not ideal in my experience as they require more caslicks (stitching of the vulva), are not great milkers, require more feeding in winter and can get bullied if mixed with larger breeds.

If the recipient mare is synchronised within four days after the donor mare’s ovulation, hormone supplementation will not be required to maintain the pregnancy.

Some people feel that the recipient mare has an influence over the foal’s temperament and even its movement. This has not been the case in my experience.

Can the embryos be frozen?

Yes, they can, but the success rate for transfer drops well below 50%, thereby the overall success of the embryo recovery and transfer is approximately 30%. This makes it expensive and impractical. In an ideal world, freezing embryos in the autumn for implanting in the spring would save a lot of work with synchronization, and would mean no disruption for competition mares in peak season.

Any recent advances?

Embryo transfer has been performed commercially for over 20 years now, but still only 3% of sport horse foals in Europe are born this way. Cost and limited success rates are the main reasons for this.

There are some centres in Europe performing oocyte recovery and Intracytoplasmic Sperm Injection. This is the recovery of several oocytes from the ovaries of mares and fertilizing these harvested oocytes in vitro. The fertilized oocyte is then grown to an embryo stage before being implanted like the ET process.

This may lead to higher success rates than ET in the future, however, at present, it is more expensive.