Since the first live foal produced by embryo transfer was born in 1974, the procedure has become one of the most popular assisted reproduction options for breeders with mares who are valuable or for mares that are to remain in competition.

During a presentation at the 2010 American Association of Equine Practitioners Convention, Patrick M. McCue, DVM, PhD, Dipl. ACT, associate professor of equine science at Colorado State University (CSU) reviewed the results of more than 490 embryo recovery procedures performed at CSU between 2004 and 2008. He discussed the flush techniques commonly used and the success rates of retrieving embryos from mares of various ages and reproductive status.

According to McCue, a majority of embryo flush procedures are attempted at Day 7 or 8 after ovulation. Flushes may be performed on day 6 or early on day 7 in an attempt to recover small embryos for cryopreservation (freezing). He typically uses four liters of fluid in an initial series of flushes, and he proceeds with another liter or two if an embryo isn’t recovered during the first round.

The average embryo collection success rate of young mares (< 15 years of age) was 57.1%, while the embryo recovery rate of older mares (≥ 15 years of age) was 39.4%. In addition, he noted that embryo collection success was significantly lower in mares that experienced prolonged uterine inflammation after mating (i.e., a prolonged period of fluid accumulation)