Tower Equine

Veterinary Surgeons


Embryo Transfer - "Flushed with Success" - February 2008

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It is all about finding that elusive balance between work and family. Can you combine both the highflying career and motherhood? And no, we’re not talking about your own juggling act for once, but your horse’s. Because it isn’t just a human dilemma these days - mares are under equal pressure to both perform and reproduce, and they have biological clocks too. By the time a mare’s competitive days are over, her peak fertility is already behind her too. If you are lucky enough to own an equine star, you want to pass on her genes to the next generation, but you don’t necessarily want her taking an enforced maternity break. So can a successful ridden career be compatible with the patter of tiny hooves? Well there is an answer, and it is called Embryo Transfer.

The idea is simplicity itself. Your mare visits the stallion or the AI clinic in the usual way, but instead of carrying the foal to term, the embryo is flushed out of her at a few days of age and popped into a second mare. Instead of a year off getting hot and heavy, your equine athlete is back in work in two weeks, leaving the surrogate mum to deal with the swollen legs and stretched abdominal muscles.

There are other advantages too. With no pregnancy to carry, the procedure is almost risk free, plus it is quite possible to repeat it, ending up with two or even three foals in one year.

Put like this it sounds to good to be true. So why isn’t everyone doing it? The rates of embryo transfer are still very low in the UK, low enough that when a top mare such as Headley Britannia is used for ET, it makes headline news.

Well the main drawbacks are technical and financial ones. For a start the transfer process itself is extremely fiddly, requiring great care, timing and attention to detail. You need two mares – your donor mare and the surrogate – to be at almost exactly the same stage of their estrus cycle. The donor mare is then covered or inseminated, and just seven days after ovulation the embryo is flushed out of her uterus. Any older than this and the embryo will not take in the surrogate mare, but at a week old it is no bigger than the full stop at the end of this sentence. Blink and you miss it. After flushing the embryo has to survive being picked up, washed and peered at under the microscope and then deposited into an entirely new uterus. It is a lot to put up with for a fragile bundle of cells.

Sheep and cattle can be ‘superovulated’ so that they produce a handful of embryos on each flush, but mares are less helpful. If you are very lucky you might get two embryos, but sometimes you can do all the work of inseminating the mare, lining up the surrogate and flushing, and end up with no embryo at all. So a little bit of luck comes in handy too.

If you are successful, and the embryo is transferred to the surrogate mare, all you can do then is cross all your fingers and wait. Ten days later an ultrasound scan will show if the pregnancy has continued to grow in its new home.

With a fertile mare and an experienced team you can expect to retrieve an embryo in about three out of four flushes, Not all of these will lead to a pregnancy however, so you have to be prepared for at least a couple of tries.

None of which comes cheap. Tot up the cost of buying and keeping one, or preferably two surrogate mares (in case you retrieve two embryos), plus all the veterinary costs, and the foal is going to arrive owing you a lot more than just the stud fee. Such an investment in time and money means that embryo transfer is unlikely to be viable for many breeders. However a foal by a proven sire out of a top competition mare can command a significant price, and in these cases the sums can more than add up.

The good news is that as the number of mares entering ET programmes increases so the costs will come down. Take for example the polo world, particularly in Argentina and Australia, where ET has been in use for many years. In Argentina top quality polo mares routinely produce four or five foals a year, even in one case ten foals out of the same mare in one year. Ten Headley Britannia foals each year. Now there’s a thought...

Roger Lee MA VetMB CertEM(Stud) MRCVS