Practical aspects of equine embryo transfer

This article focuses on practical aspects and most specific points of equine embryo transfer (EET). Induction of polyovylations in donor mares is not possible. Only the repetition of embryo collections can increase the number of foals from the same mares. At each oestrus, follow follicular growth and artificial inseminations are conducted in the same way as for any brood mare. It is essential to know the number and timing of ovulations at least a 12-hours accurency. Induction of ovulation is frequently required, GnRH agonists are used to do that. Embryos are flushed from the donor mare’s uterus, typically on day 7 or 8 after ovulation using a long (~1.5 m) and large (diameter 8 mm) Foley-type balloon-tipped catheter introduced by vaginal route just in front to cervix. Some practical details are important to EET practitioners, firstly, the embryos are easily located under stereo-microscope after filtration of flushing medium, and secondly most equine embryos are immediately transferred or after cooling at 4°C less than 24 hours. To have a recipient mare in the right stage of her oestrous cycle (D5 to D8 after ovulation) is the biggest and the most difficult challenge for EET practitioners because the synchronisation of oestrous and ovulations is very difficult to obtain. Therefore, embryos are transferred transcervically to the uterus of a recipient mare. Recently, a modified method using a speculum and a specific forceps seems to give a much better success rate than the conventional technique which requires a large training. The EET has regulatory constraints: regulations of different breeds allowing or not allowing the embryo transfer and sanitary European regulation concerning intra-community trade of equine embryos (Annex D to Council directive 92/65 EEC) and, in some countries, additional national regulation. The possible sanitary risks of ET in equine have been still little studied, and without International or European official registrations of EET activity, it is difficult to know the extent of the use of the technique around the world. The average success rate of embryo recovery is of the order of 40 to 50% depending on the fertility of the donor and the type of sperm used, the transfer success rate can reach 70 to 80% if the technique is well mastered by ET practitioners.