Embryo biopsy and vitrification applied to a commercial embryo transfer program in Argentina

Use of embryo vitrification (EV) would have multiple advantages in a commercial embryo transfer (ET) program. EV would allow embryos to be transferred so that foals were born in early spring, which is preferred in Argentina due to health problems in foals that are born in late spring-summer. Currently, many high-level Polo mares compete in the spring, and the potential for embryo production from these mares is thus lost. EV would allow embryo storage against future loss or sale of a mare and allow owners to control which embryos were transferred in any given season. EV would also help the ET Center, by spreading work out through the breeding season and simplifying recipient synchronization. To explore the use of EV in our program, we compared pregnancy rates after transfer of vitrified-thawed vs. fresh embryos. Embryos were recovered on Day 7 to 8 post-ovulation from donor mares in our clinical program at Doña Pilar in September 2021 to May 2022 (Season 1) and then vitrified, and in September 2022 to January 2023 (Season 2) and transferred fresh. All embryos were transferred during Season 2. Fresh embryos were either biopsied via micromanipulation for sexing by PCR (BF, n=136) or were not biopsied (client did not request sexing orthe embryo was considered too small to biopsy,