First field results on the use of stallion sex-sorted semen in a large-scale embryo transfer program.

Flow cytometry sex-sorting technology was developed in 1989. However, it is only the bovine species in which offspring of the desired sex are obtained at a commercial level. The aim of the present work was to evaluate efficiency parameters when using fresh sexed semen in a large-scale equine commercial embryo transfer program. During the 2009, 2010 and 2011 breeding seasons, 938 synchronized cycles were artificially inseminated. One hundred (10.6%) mares failed to ovulate, and for the remaining 838 useable cycles, 887 doses of sexed semen were used, representing 1.06 doses per cycle. In general, 435 (51.9%) out of 838 flushing performed resulted in the recovery of at least one embryo and 496 (59.1%) embryos were recovered, including twins and triplets. Pregnancy rate at 25 days achieved 81.5% (one embryo transferred per recipient). Embryo recovery rate was not statistically different either between preovulatory and postovulatory artificially inseminated mares or when increased quantities of sexed sperm per dose were used (15-45 million) (P > 0.05). A broad variation in embryo recovery rate was observed between the different stallions used in this study. Sex accuracy of the sex sorting assessed by ultrasound fetal sex determination was 90.3%. Finally, overall efficiency (female embryo pregnancies per useable cycles) was 39% (325/838), meaning that to obtain a female pregnancy of at least 75 days it was necessary to perform 2.5 flushing.