Cumulus cell DNA fragmentation as non-invasive biomarker of equine oocyte quality in in vitro embryo production

Context The efficiency of in vitro embryo production in animal species is constrained by the absence of practical, non-invasive biomarkers to assess oocyte quality. Cumulus cell DNA fragmentation index (CC-DFI) has been proposed as a biomarker in humans, but data in animals remain limited. Aims This study investigated the association of CC-DFI with in vitro maturation (IVM) and intracytoplasmic sperm injection (ICSI) outcomes in horses, and its relationship with mare-related factors, autumnal transition period, cumulus cell viability, and cumulus expansion. Methods Cumulus–oocyte complexes (COCs) retrieved via ovum pick-up were subjected to IVM. Immediately after denudation, CC-DFI for each mare was assessed using a chromatin dispersion assay across 54 ICSI sessions. Viability was assessed based on membrane integrity, and expansion was quantified as the relative change in total COC area. Only mature oocytes were selected for ICSI and subsequent in vitro culture. Key results Oocyte maturation rate and cleavage rate were not associated with CC-DFI, whereas total blastocyst rate and yield were significantly negatively associated with CC-DFI. Blastocyst yield at day 7 was also significantly negatively associated with CC-DFI, whereas no associations were found with grade 1 blastocysts. No significant associations of CC-DFI with mare-related factors, autumnal transition period, cumulus cell viability, and cumulus expansion were observed. Conclusions In conclusion, this study supports CC-DFI as a potential biomarker for predicting oocyte developmental potential in equine ICSI, particularly blastocyst formation. Implications CC-DFI could help improve oocyte selection and embryo production efficiency in equine ICSI programs, but further validation is required before routine clinical use.