Abnormal early cleavage may flag higher pregnancy loss in horse embryos
CURRENT BRIEF VERSION: Abnormal cleavage patterns during the earliest cell divisions of equine in vitro-produced embryos were linked to substantially worse pregnancy outcomes in a new retrospective study from researchers at the University of California, Davis and collaborators. In embryos transferred after time-lapse monitoring, early pregnancy loss was 53.3% for embryos with abnormal cleavage patterns, versus 22.6% for normally cleaving embryos, and pregnancy success was also lower overall. The paper, published online ahead of print in Equine Veterinary Journal on July 31, 2025, argues that first-division morphokinetics could help fill a longstanding gap in standardized quality grading for equine IVP embryos. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinarians working in equine reproduction, the findings suggest embryo selection may be improved before transfer, not just by grading blastocysts later in development, but by tracking how the embryo divides at the very start. That matters because equine IVP has expanded quickly, yet pregnancy loss remains a practical and economic concern, and existing grading systems adapted from cattle don't reliably predict outcomes in horses. Prior work has also shown that pregnancy odds are shaped by more than morphology alone: slower embryo development, poor post-thaw grade, advanced donor mare age, and later-season transfer all reduce pregnancy rates, while donor mare and stallion effects are usually modest overall but can differ sharply in some mare-stallion combinations. (pubmed.ncbi.nlm.nih.gov)
What to watch: Whether time-lapse morphokinetic screening becomes part of routine commercial IVP workflows, and whether future studies tie these abnormal cleavage patterns to chromosomal errors or other biological causes of loss. Another practical question is how these early cleavage markers will perform alongside already recognized predictors such as development speed, post-thaw embryo quality, donor mare age, seasonality, and specific mare-stallion pairings. (cehhorsereport.vetmed.ucdavis.edu)