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In the past two decades the biggest advance in the breeding of the non-Thoroughbred horse has been the arrival of artificial insemination. With its very many advantages, this has given a great boost to performance horse breeding. Now we have another big step on the breeding ladder – Embryo Transfer (ET).
There are non-surgical and surgical options available.
The non surgical approach has meant that this procedure is now a realistic proposition. The obvious, and enormous, advantage is cost. General Anaesthetic is not necessary.
Equine ET involves collection (flushing) of an equine embryo from the donor mare and transfer of that embryo into the uterus of a surrogate (recipient) mare. If the surgical route is chosen the embryo is injected directly into the uterus of a recipient mare while she is under general anaesthetic. In the non-surgical transfer, the embryo is introduced into the uterus of a recipient mare via the vagina with the aid of a uterine transfer catheter. For this procedure, the recipient mare needs only to be restrained i.e. with the use of stocks and mild sedation if necessary.
The success rate with the surgical transfer is higher (up to 90%) in comparison with the non-surgical option but never the less this can be very high as well 80-85%.
The disadvantages of a surgical ET, apart from the cost for the breeder is the limitation of a ‘reproductive life span’ for recipient mares (internal scarring, and the possibility of adhesions between gut and uterus following surgery) The non-surgical approach is the technique of choice for equine ET with most veterinary surgeons.
In the first step of the transfer, we have to select a suitable recipient mare, this is most important. The recipient should, ideally, be between the ages of three and nine years. She may be a maiden mare, or have had a few foals in the past, but should be classed as an ‘easy breeder’. The recipient must be good to handle and of a suitable size, i.e. draught cross type.
The next step is the synchronisation of the reproductive cycles of the donor and recipient mares with the aid of hormonal therapy. Ideally the recipient mare should ovulate as close to the donor as possible. This must be within the window of 24 hours before to 72 hours after the donor mare. This is not achieved easily; therefore we prefer to synchronise a minimum of two or even more recipients for each donor mare.
All the mares are examined daily with the help of ultrasound in order to establish the stages of the cycles and estimate ovulation times. The donor mare is then inseminated, or mated, at the optimum time. (In order to increase our chances of final success we prefer not to use frozen semen). The embryo collection procedure is carried out approximately on day seven and a half, post ovulation. If left any longer the embryo would be too big, and therefore too fragile to transfer and if the flushing were performed any earlier there would be a high risk of the embryo not having yet reached the uterus. This usually happens on day five, post ovulation.
To flush the embryo from the uterus of a donor mare, we use a balloon-ended catheter inserted in to the uterus. The balloon is then inflated with air. This creates a water tight seal against the internal side of the cervix. We use between one and three litres of a sterile fluid to distend the uterus. The ready made flushing fluid, which is a salt solution contains an antibiotic, which counteracts any possible contamination. There is also a protein source i.e. bovine serum albumin, to prevent the embryo ‘sticking’ to the internal walls of the flushing circuit.
In the next stage the fluid is siphoned from the uterus and then filtered through a special embryo filter. The contents of which are examined under a microscope. A seven and a half day old embryo is about half a millimetre in size. Following the successful recovery the embryo is then flushed several times with a different concentration of flushing and holding medium. When this is completed the embryo is loaded into the uterine transfer catheter. The chosen recipient is restrained in the stocks and sedated only if necessary. The veterinary surgeon then introduces the catheter through the cervix into the uterus and deposits the embryo.
After the embryo transfer procedure one has to wait for a minimum of five days before the pregnancy can be revealed on a scan of the recipient mare.
Even though the non-surgical embryo transfer technique has become more and more successful in recent years, it is not an easy procedure. Even the more simple stages have to be performed to perfection otherwise the transfer will fail.
We can now produce between three and five foals in one breeding season out of mares who are at their peak performance or are showing potential to go all the way to the top. This can carry on for a number of years. There is a small interruption to training or competing schedules,.
Bourton Vale hosted a client evening at the Adlestrop Village Hall on Wednesday 1st Novewmber. The evening was kindly sponsored by Boehringer Ingleheim and was a huge success; allowing attendees to meet the new members of our team and have an introduction to a variety of topics.