Embryo Transfer (ET) allows Breeding from the Best

If the desired objective is to improve one’s stock by breeding better horses rather than just buying the best whatever the price, the way to do it is to Breed the Best from the Best. To improve the chance of breeding winners at a higher level within one’s lifetime it is advantageous to speed up the process by obtaining several foals each year from the very top mares rather than breeding from all one’s mares and waiting to see which is the best.

Embryo Transfer (ET) is the most widely used assisted reproductive technique for genetically superior mares.

The first successful equine embryo transfer was reported in 1972. However, it was not until the early 1990s that embryo transfer became an accepted clinical procedure in the equine breeding industry. Over the last few years ET has improved with the use of non-surgical transfer methods and is achieving high pregnancy results of up to approximately 70%.

By using ET you have the opportunity of breeding a foal from the highest performing mare without interrupting her showing or competitive career. It is also possible to obtain foals from mares that are incapable of carrying a pregnancy to term, e.g. mares with age related endometrial changes, early embryonic loss or mares with non-reproductive health problems which make carrying a foal to full term and rearing it unadvisable.

The process of embryo transfer is as follows:

Having carefully assessed that your mare is good enough to be worth investing in, you must choose a stallion.

Arrange for the mare to be inseminated by AI or natural service.

Seven or eight days after ovulation has taken place the uterus is flushed and hopefully an embryo recovered; it is then transferred into a well synchronised recipient mare.

The recipient mare is scanned after a further seven or eight days and if in foal, once again at twenty eight days after conception to confirm a heart beat and then a third scan at forty two days to confirm all is well.

The process requires a collaborative approach between the manager of the mare and the veterinary surgeon that is going to do the work and will have selected suitable recipient mares. The process is ideally carried out at a specialist reproductive centre with experience of ET and a herd of recipient mares from which to choose two whose oestrous cycles are running in parallel with the donor mare. The veterinary surgeon will carefully monitor the donor mare’s follicular development by rectal ultrasonography and decide on the precise timing of service. The embryo will be flushed seven to eight days post ovulation and transferred into one of two previously prepared recipient mares.

The Recipient Mare
At Twemlows Hall we have a herd of about ninety young, healthy and reproductive sound recipient mares. This allows us to select most carefully two recipients for each donor mare; they should be of about the same size as the donor mare or slightly larger. They should be from 4 to 14 years of age. It is advantageous but not always possible to use mares that have had at least one foal.

As soon as the embryo has been found the two recipient mares are prepared for the non-surgical embryo transfer. The decision as to which one to use is not made until just moments before the transfer is made. The veterinary surgeon will decide on examination which of the two mares has the best cervical and uterine tone to receive the embryo.

Transported Embryo Service. Specialist ET centres with a large herd of recipient mares have a big advantage over the veterinary practice which does not have this facility because they are able to choose a suitable recipient from a large number of mares; but distance and the cost of travelling mares can be a deterrent. This has resulted in veterinary surgeons many miles from Twemlows Hall working closely with Noelle Lowry, the in house equine reproduction veterinary surgeon by operating a “Transported Embryo Service” service. The distant veterinary surgeon prepares the donor mare and collects the embryo which is then packaged and chilled in an equitainer which is taken by courier to Twemlows Hall for transfer into an already prepared recipient mare.

Clearly this procedure requires great co-operation between the two veterinary surgeons and it is important to make plans well before the donor mare is inseminated.

With careful planning ET can be carried out with very little interruption to the mare’s competitive programme