Embryo transfer simply involves the removal of an embryo from the uterus of one mare and transferring into the uterus of another mare.
This procedure is suitable for all sport and performance horses. In particular it is a beneficial assisted reproductive exercise for:
Ideally the best donor mares are mature, reproductively healthy mares. In order to maximise success rates, detailed attention needs to be paid to the donor mare and the recipient in relation to timing of ovulation.
The donor mare is examined daily while in season by palpation and ultrasound in order to determine the exact time of ovulation. Recovery of embryos is usually attempted on day 7 (ovulation day is day 0). Day 6 and day 8 embryos can be transferred, but the success rate diminishes dramatically after this time.
A sterile catheter is inserted through the cervix and into the uterine body and the uterus is then filled with a special flush media. This media is then allowed to flow back through the catheter and passed through a filter which traps the embryo. The contents of the filter are then poured into a dish and examined for the presence of an embryo under a microscope.
Embryos that are day 7 are generally less than 1mm in diameter. The embryo is then graded from 1 to 5, grade 1 and two being ideal and grade 5 as of no value. The recovered embryo is then washed and maintained in holding media until transferred into a recipient mare.
Embryo recovery rates may be as high as 75% or as low as 25%. Factors that influence this recovery rate are:
It is critical that the oestrous cycle and the day of ovulation of the recipient mare is closely synchronised with that of the donor mare. Ideally the recipient mare should ovulate from one day before and no more than three days after the donor mare. Ovulation dates outside of this synchronisation will dramatically reduce transfer success rates.
As the act of synchronisation cannot be an exact science, it is therefore best to try to synchronise at least 2 to 3 recipients in order to obtain one that would fit into that critical window. Ideally it is best to have the recipient ovulate 1 to 2 days after the donor.
The embryo is transferred non-surgically using a specialised embryo transfer instrument which is passed through the cervix and the embryo is deposited into the uterus. At this stage it is not unusual to administer certain medications to enhance the success rate of the transfer by helping the mare maintain the transferred embryo.
As the embryo is already 7 to 8 days old when transferred it only needs another 4 to 5 days before the embryo can be observed with ultrasound to determine if the transfer has been successful.
The success rate of transfer is usually about 70%. It is important to follow up with subsequent pregnancy examinations as some recipient mares do not stay pregnant to term with the majority of these losing their pregnancy prior to 50 days. This is more likely to occur when using older donor mares and when the embryo transferred is of a lower grade.
We are a well-established equine practice servicing South Auckland and the greater Auckland area. With our purpose-built hospital and surgical facilities our experienced staff are able to provide quality care with a full range of medical, diagnostic and surgical services.
