One of the popular Table Topics sessions held at the 2010 American Association of Equine Practitioners Annual Meeting, held Dec. 4-8 in Baltimore, Md., revolved around equine embryo transfer.

The session opened with a discussion on donor mare management. Many donor mares in embryo transfer programs are older and have a history of reproductive problems, including fluid accumulation in the uterus after breeding (i.e., persistent mating-induced endometritis). Table Topic attendees agreed that donor mares should be examined by ultrasound and samples should be collected from the uterus for culture and cytology. If a mare has a history of fluid accumulation after breeding, a uterine lavage and oxytocin therapy 4-6 hours after breeding might be beneficial in limiting the inflammatory response to spermatozoa. Oxytocin might be used one to four or more times per day to promote uterine contractions and to assist with fluid evacuation. In some mares prostaglandins (i.e., cloprostenol) might be more effective at stimulating uterine contractions and fluid evacuation. However, prostaglandins might be associated with side effects such as sweating, abdominal contractions, and diarrhea. In addition, prostaglandins are not generally recommended after ovulation due to adverse effects on development of the corpus luteum (which forms from the tissues remaining after a follicle ruptures at ovulation). Attendees also mentioned that some practitioners routinely use antibiotics after breeding or flushing the donor mare.

Embryo recovery techniques also were reviewed, including the optimal day to flush (usually Day 7 or 8) and media available for flushing mares. A majority of practitioners in the session indicated that they use a commercially prepared complete flush medium. In contrast, some practitioners use lactated Ringer's solution, with or without a surfactant (surface-active substance) added.

Synchronization of recipient and donor mares was discussed. Historically veterinarians have recommended that the recipient mare ovulate between one day before and up to two days after the donor mare. Recent studies, however, have suggested that the recipient mare can ovulate three to four days after the donor mare and pregnancies achieved after transfer.

Quality and management of recipient mares are key components of a successful embryo transfer program. Use of transitional (between diestrus and regular estrous cycles) or anestrus (not showing estrus) mares as recipients was discussed. If a synchronized cycling recipient is not available in late winter or early spring, a transitional mare treated with progesterone can be used. Alternatively, a mare in deep season anestrus treated with estradiol for three to five days and then administered progesterone beginning one day after ovulation of the donor mare can be used.

Equipment and techniques for transfer of recovered embryos also were reviewed. Small embryos (i.e. less than 1,000 µm) are often transferred with a straw and Cassou artificial insemination (AI) gun system, whereas larger embryos (i.e. greater than 1,000 µm) are often transferred with an AI pipette. The technique of transferring the embryo is where the "art" of embryo transfer meets "science." Development of sound clinical skills is critical for a high success rate.

This session was moderated by David Hartman, DVM, of the Hartman Equine Reproduction Center in Whitesboro, Texas, and Patrick McCue, DVM, PhD, Dipl. ACT, of Colorado State University.

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