Abnormal embryo cleavage linked to early pregnancy loss in mares
CURRENT BRIEF VERSION: Abnormal cleavage patterns during the first cell division of equine in vitro-produced embryos were linked to markedly worse pregnancy outcomes in a new retrospective study from researchers at the University of California, Davis, and collaborators. Reviewing time-lapse images from 70 transferred embryos and 114 arrested embryos, the team 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 blastocyst formation also improved the odds of a day-14 pregnancy and reduced loss through day 25, adding to earlier equine data showing that slower embryo development, poorer post-thaw grade, advanced donor mare age, and later-season transfer can all reduce pregnancy rates after transfer of in vitro-produced embryos. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For equine reproduction practices using ICSI and other in vitro embryo production workflows, the findings point to a practical, non-invasive way to refine embryo selection. That could matter because IVP embryos have historically shown higher early loss than in vivo-derived embryos, even though larger retrospective data suggest IVEP is generally efficient: 85% of successful 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. Prior work also suggests mare and stallion identity usually have a modest effect overall, but some underperforming donor mares can have pregnancy rates that differ by as much as 50% depending on the stallion used. (pubmed.ncbi.nlm.nih.gov)
What to watch: The next step will be whether clinics adopt time-lapse morphokinetic grading prospectively, and whether larger studies confirm it improves live foal rates, ideally alongside embryo selection and transfer decisions that also account for donor mare age, embryo quality, season, and occasional mare-stallion interaction effects. (pubmed.ncbi.nlm.nih.gov)