EMBRYO TRANSFER – Frequently Asked Questions

From the September 2013 issue of The Stable Magazine – www.thestablemagazine.com/september2013

What is Embryo Transfer?

Embryo Transfer is the process of fertilising an egg (from a mare who is a successful competition or show horse, or perhaps from one who is not able to carry a foal to term), harvesting the resulting embryo and transferring it into a recipient mare, who can then carry to foal to term, give birth and care for the foal until it is weaned. 

What are the advantages of ET?

The main advantage with Embryo Transfer is the fact that mares who are not able to carry a foal to term may still reproduce. If your mare is a particularly valuable horse, putting her in foal does come with some associated risks. Through using a recipient mare, you are still able to have a foal from your mare without the risk of complications to your mare during pregnancy or foaling.

If you have a mare with a particularly intense competition schedule, ET might be preferable to taking her out of work until the foal has been weaned. If you’re breeding on a large scale, it is possible to have more than one foal from your mare in a season, with the option of harvesting multiple embryos and transplanting them into more than one recipient mare. ET also allows foals from older mares to be carried by recipient mares - or mares who have previously had complications foaling or carrying a foal to term.

Designer babies!

Will we get to the stage where you can select a stallion and a mare from out of a catalogue and order your own designers foal embryo? Quite possibly! Frozen embryo sales are becoming more popular as technology for AI and ET improves. What’s next on the cards? Research suggests that sexing embryos is possible - or fertilising embryos with sex-selected sperm. While the techniques are still being improved, this could well be an option in the future.

Is ET available in Australia?

Yes! There are a number of specialised veterinary practices around the country that are able to assist you in facilitating the ET process. ET is growing in popularity both in Australia and overseas. It is much less expensive to import a live (frozen) embryo than it is to import a mare in foa. Many breed societies will allow foals born as a result of ET to be registered and to compete, with the exception of Thoroughbreds, as the Australian Studbook does not allow foals born as a result of artificial insemination to be registered or race.

What costs are involved?

According to our research on various clinics around Australia, the average successful embryo transfer foal would cost anywhere between $2000-$4500. Of course, much of this depends on the viability of the eggs from the donor mare, use of a suitable recipient mare and breeding with good quality semen. Much of the cost involved relates to the recipient mare. Clinics that specialise in ET often run their own band of recipient broodmares - horses that have been checked and screen as suitable candidates to carry and raise ET foals. The more mares in their prospective broodmare herd, the more likely they are to have a suitable recipient ready for their clients.

What does the recipient mare contribute to the process?

The recipient mare is the mare who will carry the embryo (foal) to term, foal, and be a surrogate mother to the newborn until weaning. The recipient mare does not contribute genetic information to the embryo, although the size of the recipient mare may affect the height of the foal. As the recipient mare will also raise the foal she may ‘pass on’ some characteristics and mannerisms to the foal.

What qualities should a recipient mare possess?

Ideally, recipient mares will be proven breeders in good health, and will not have had any prior foaling problems. The history of a recipient mare should be carefully considered before she is used for the purpose of embryo transfer. Up to three recipient mares may be required for one successful embryo transfer, as synchronisation between the donor and recipient mares is required for successful embryo transfer.

It is important to note that not all good recipient mares (who are healthy and physically able to carry the foal to term) make ideal surrogate mothers. The recipient mare is also required to raise the foal until it is of weaning age.

How does the quality of semen affect the end result of embryo transfer?

As with ‘conventional’ breeding methods, and indeed, artificial insemination, the quality of the semen used does have an effect on the success rate of Embryo Transfer. Poor quality semen (with less viable or small numbers of sperm) can greatly reduce the success rate of breeding a foal.

Fresh semen is preferred. Chilled and frozen semen have slightly lower success rates in general, although many other factors influence the quality of semen. Frozen semen has the advantage of being easily transported - interstate or overseas, provided it is kept in optimum conditions.

How many embryos are you likely to get from the donor mare?

Donor mares can have embryos collected at each ‘cycle’. So every 19-21 days, donor mares can be flushed. Some mares will have ‘double ovulations’ and can produce two embryos in a cycle. Embryos are not guaranteed at every flush. Once embryos are harvested, they are washed, cleaned and examined for viability.

What are the chances of a live foal on the ground eleven months later...?

ET is advancing at a good rate/ According to our research, working with a good quality, viable embryo, good quality sperm, and a healthy recipient mare, horse owners can expect at least 75% of donor mares to conceive.

When is a mare a good candidate to be an embryo transfer donor?

Donor mares must be healthy and in good condition - and they should be thoroughly examined before the ET process is undertaken. Ideally, younger donor mares (under twelve years of age) who cycle regularly have the highest success rate and produce better quality embryos. The quality of the embryo from the donor mare has a lot to do with your chance of success. Mares that have not been able to conceive previously may have lower quality embryos, or produce fewer embryos than mares who conceive easily. Mares who have a previous history of low conception rates - while good candidates for ET (as the most viable embryos can be selected) - may only give a 30% success rate. This is worthwhile if preserving the mare’s bloodlines is very important to the breeder, although time and expenses are involved should be weighed up against the possibility of no resulting foal. The reasons the mare may not have been able to successfully conceive may or may not be overcome using the embryo transfer process. In this case, an examination and veterinary advice should be sought for the best course of action.

What is the process for ET?

In a nutshell...

The donor mare should be examined by a vet to determine her cycle and time of ovulation. Artificial lighting may be used to regulate the cycle. The aim is to determine the day of ovulation, optimum breeding times, and hopefully, to be able to co-ordinate a recipient mare. The donor and recipient should be synchronised for the best results.

The donor mare is bred (either by fresh, chilled or frozen semen). Embryos are then flushed from the donor mare at around day 7 or 8 after ovulation in a non-surgical procedure. They are graded according to viability. Embryos that appear viable are scored a ‘1’ or a ‘2’, and produce success rates of around 70-80% at 14 days.

Embryos can be transferred to the recipient mare immediately (either surgically or non-surgically), or they may be chilled to allow a 24 hour window for implantation. (Useful when transporting an embryo from one stud or property to another!) Embryos can also be frozen - for which they are usually collected on day 6 after ovulation.

Embryos are then implanted into a recipient mare who has ovulated as close as possible to the donor mare. A pregnancy test can be performed as close to five days after the embryo transfer has occurred.

Is it an option for my mare?

While it might seem like the ideal solution if you compete with your mare every weekend, Embryo Transfer isn’t something to be taken lightly. As with breeding a foal of your own the conventional way, there are associated costs, financial outlay, and there is no 100% guarantee that you’ll end up with a foal. Success rates are improving, and if conditions are right (a viable egg from a donor mare, good quality semen, and a healthy recipient mare) there is obviously a greater chance of the process resulting in a live foal.

Your mare should also have outstanding bloodlines and wonderful qualities that you’d like to pass on to a foal. (Same as if you were considering breeding her in the conventional way.) The only real difference is that Embryo Transfer does offer mare owners the opportunity to breed from mares that otherwise, may not be able to carry a foal to term.

Embryo transfer takes considerable organisation, preparation, planning, time and financial outlay. If you’re thinking that embryo transfer might be something you’d like to consider - do your research, speak to your veterinarian and find out whether ‘on paper’ your mare would be a good candidate before you go booking in ultrasounds and paying your deposit on a stud fee for this season.

This article was originally published in the September 2013 issue of The Stable Magazine – Australia’s FREE Online Horse Magazine. Read this article and many more online at www.thestablemagazine.com