Given the right conditions, equine embryos produced in a lab using ICSI can lead to pregnancy rates of approximately 70%, researchers say. | Photo: iStock

“The good thing about these in vitro embryos is that they’re very small compared to flushed embryos, and they don’t have that embryonic capsule,” fluid that causes issues with cryopreservation (freezing), said Anthony Claes, DVM, PhD, Dipl. ACT, assistant professor in equine reproduction at the Utrecht University Faculty of Veterinary Medicine, in the Netherlands.

Claes and colleagues produced 261 equine in vitro embryos using intracytoplasmic sperm injection (ICSI) and cultured them up to the blastocyst stage. Then, they froze (cryopreserved) them and stored them—some for up to two years, he said. Later, they thawed the embryos and implanted them in recipient mares at four, five, or six days after ovulation. Finally, the researchers investigated other factors that might influence pregnancy success, such as mare age and management, season, and more.

Overall, they found 56% pregnancy rate up to 37 days after implantation. However, of those, 16% failed before 42 days of gestation, he said