Embryo Transfer by Matt Hecking
I
n simple terms embryo transfer involves the removal of an embryo from the uterus of one mare and transferring into the uterus of another mare.
Is my mare a suitable candidate?
This procedure is suitable for all sport and performance horses. It can be ideal in the following circumstances:
u Mares in competition can donate embryos while in work u Valuable mares may have more than one foal per year u Sub fertile mares can have their embryos transferred to young, reproductively healthy mares
u Older mares can donate embryos to young recipients u Mares with a damaged cervix as a result of a difficult foaling can have embryos transferred
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.
How does it work?
The first phase of the process is a standard AI cycle using either fresh or chilled semen. The donor mare is examined daily while in season by palpation and ultrasound in order to determine the perfect time to inseminate with semen from your choice of stallion. 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 aſter this time.
To perform the flush 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 2 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:- u Age and fertility of donor mare u Quality of semen used u Day of recovery u Number of ovulations
28 April/May 2020 For the latest news visit
www.centralhorsenews.co.uk The flushing process A recovered embryo
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 aſter the donor mare. Ovulation dates outside of this window 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 aſter the donor.
The embryo is transferred non-surgically using a specialised embryo transfer gun which is passed through the cervix and the embryo is deposited into the uterus. As the embryo is already 7 to 8 days old when transferred it only needs another 4 to 5 days before we perform a pregnancy scan using ultrasound to determine if the transfer has been
Sud vet Vicky Marchi ultrasound scanning a mare.
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