Redefining safety standards: a large-scale comparative analysis of bovine versus murine models for medical device embryotoxicity testing

PURPOSE: To overcome the limited sensitivity of the standard mouse embryo assay (MEA) for embryotoxicity screening of assisted reproduction devices and to assess the bovine embryo assay (BEA) as a suitable alternative. METHODS: In a large comparative laboratory study, sperm selection, fertilization, and embryo culture media from two suppliers (Vitrolife and Genea Biomedx, respectively) were used to generate bovine blastocysts from cumulus-oocyte complexes obtained from slaughterhouse ovaries and inseminated with frozen semen from the same bull (BEA). Bovine culture media were used for the control group. BEA assessed the following in the three groups: cleavage; blastocyst development and kinetics; post-warming re-expansion/hatching; total cell number; inner cell mass (ICM) and trophectoderm (TE) allocation; and ICM/TE ratio. In parallel, the culture media from both suppliers were tested using mouse cumulus-oocyte complexes that had been inseminated with epididymal sperm (IVF-MEA) and in vivo-derived one-cell embryos (standard MEA). RESULTS: BEA detected differences consistent with reduced developmental competence and embryo quality across 4118 bovine oocytes (≥ 4 independent cycles; ≥ 50 oocytes/group). Sperm selection media performed similarly. Regarding fertilization media, the bovine control yielded higher day 8 blastocyst rates than Vitrolife (P < 0.005), while Genea Biomedx exhibited superior blastocyst quality indicators than Vitrolife (P < 0.05). For embryo culture media, the bovine control outperformed Genea Biomedx, with Vitrolife performing intermediately (P < 0.05). Multiple kinetic, hatching, first lineage allocation and survival endpoints were reduced for Genea Biomedx (P < 0.05). Standard MEA found no significant differences, whereas IVF-MEA (1028 oocytes) detected a difference in day 4 blastocyst yield only. CONCLUSION: BEA revealed functional and quality differences between media not detected by mouse assays, supporting BEA to strengthen safety assessment while reducing animal sacrifice.