Abnormal cleavage tied to early loss in equine IVP embryos

Abnormal cleavage patterns during the first mitotic division of equine in vitro-produced embryos were linked to substantially worse outcomes after transfer, according to a retrospective study published online ahead of print in Equine Veterinary Journal on July 31, 2025. Researchers from UC Davis and Burns Ranch analyzed time-lapse images from 70 transferred embryos and 114 arrested embryos, and found that embryos with abnormal cleavage patterns had a total early pregnancy loss rate of 53.3%, compared with 22.6% for embryos with normal cleavage patterns. Earlier vitrification, used here as a proxy for faster blastocyst formation, was also associated with better day-14 pregnancy odds and lower loss through day 25. Those findings line up with broader equine IVP data showing that slower in vitro embryo development is linked to lower pregnancy rates after transfer. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For equine reproduction practices, the study points to a more objective way to rank IVP embryos before transfer. Equine IVP still lacks standardized embryo classification criteria, and pregnancy loss after transfer is a persistent clinical and economic challenge. That challenge sits within a system that is otherwise quite efficient: in a separate retrospective analysis of 2,292 IVP blastocyst transfers, 85% of successful IVEP sessions produced at least one pregnancy, rising from 78% when only one blastocyst was produced to 91% with two and 98% with three or more. That study also found that slow embryo development, poor post-thaw grade, advanced donor mare age, and later-season transfer reduced pregnancy rates, while donor mare and stallion identity usually had only modest effects overall—though some mares performed much better or worse depending on the stallion used. UC Davis says its time-lapse system is designed to track cleavage and other developmental milestones without repeatedly removing embryos from incubation, and the authors argue those early morphokinetic signals could help identify embryos with higher pregnancy potential. That could improve recipient mare use, counseling for pet parents and breeders, and overall efficiency in ICSI-based programs. (pubmed.ncbi.nlm.nih.gov)

What to watch: The next step will be whether these morphokinetic markers are validated in larger, prospective studies and incorporated into routine embryo selection protocols across commercial equine IVP programs. It will also be worth watching whether labs combine cleavage-based grading with other known predictors of success, including donor mare age, post-thaw embryo grade, seasonality, and mare-stallion pairing in underperforming donors. (pubmed.ncbi.nlm.nih.gov)