55 Relationship between genomic estimated breeding values for single blastomeres and the corresponding calves derived from in vitro-produced embryos in Japanese Black cattle

Preimplantation genomic evaluation combined with in vitro embryo production has drastically accelerated genetic improvement in cattle. We reported that possibility for the genomic evaluation using a single blastomere derived from in vitro-produced embryos at the 8-cell stage in the last IETS meeting (Yoshioka et al. 2023 Reprod. Fert. Dev. 36, 186). The aim of this study was to clarify the relationship between the genomic estimated breeding values (GEBVs) of a single blastomere collected from the 8-cell stage embryo and the corresponding calf from the embryo having the remaining seven blastomeres. Immature oocytes collected from Japanese Black cattle using transvaginal ovum pickup were matured, fertilized in group, and cultured in microwells. In the blastomere separation (BS) group, after removal of the zona pellucida with 0.25% pronase, the blastomeres were separated through pipetting, and a single blastomere was collected for SNP genotyping. The embryos having the remaining seven blastomeres were cultured to the blastocyst stage (n = 51). In the control group, intact embryos were cultured to develop to the blastocyst stage (n = 53). Calves paired with single blastomeres were produced by embryo transfer either freshly or after vitrification (n = 7). Both of single blastomeres and the hair root cells from corresponding calves were subjected to DNA extraction, and SNP genotyping was performed using SNP Chip. The GEBVs of carcass weight, ribeye area, rib thickness, subcutaneous fat thickness, yield rate, and beef marbling score were predicted using the genomic BLUP method. The blastocyst developmental rate on Day 7 (Day 0 = IVF) was higher in the BS group than in the control group (84.3% [43/51] vs. 64.2% [34/53]; P < 0.05). The call rate for an individual, the accuracy of SNP genotypes, was 70.42%–88.82% in single blastomeres. On the other hand, the corresponding calves were as high as 99.98%–99.99%. There was a positive correlation between single blastomeres and the corresponding calves in GEBVs for all six carcass traits examined. High correlations were found for rib eye area, subcutaneous fat thickness, yield rate, and beef marbling score in GEBVs (r = 0.81, 0.89, 0.86, and 0.83, respectively, P < 0.05). Our results showed that calves were obtained from cryopreserved blastocysts after analysis for GEBVs using a single blastomere collected at their 8-cell stage. Moreover, the GEBVs from a single blastomere could be used to predict those of the corresponding calves. These findings suggest the possibility of preimplantation genomic evaluation with high blastocyst developmental rate using single blastomeres in Japanese Black cattle.