Abstract: This study aimed to establish a method that can assess the chromosomal quality and production performance of early bovine embryos, and provide technical support for the industrial application of bovine in vitro embryos. In this study, 27 in vivo blastocyst, 21 in vitro blastocyst, 6 in vitro 2-cell embryos and 5 in vitro 8-cell embryos were selected, and the embryonic cell samples with different cell numbers of in vivo embryos and in vitro embryos were obtained by embryo splitting technique. Among that, in vivo embryos were divided into two groups, one was in vivo trophectoderm cells (tec) group (splitting some of the tec from the in vivo blastocyst), the other was the half in vivo embryo group (splitting half of the embryo from the in vivo blastocyst). The remaining groups were in vitro tec group (splitting some of the tec from the in vitro blastocysts), in vitro 2-cell embryo group (splitting one blastomere from the in vitro 2-cell embryo), and in vitro 8-cell embryo group (splitting one blastomere from the in vitro 8-cell embryo). After embryo splitting, whole-genome amplification (WGA) was conducted, and the samples with successful amplification (DNA amounts greater than 1 000 ng) were subjected to SNP chip detection. Data with a call rate greater than 90% were evaluated for production performance, those below 90% were subjected to chromosomal fragment deletion analysis and data filling. The results showed that:1) After splitting part of the trophectoderm cells, the developmental rates of bovine in vivo embryos (remaining portion of in vivo blastocysts after splitting some of the tec) and bovine in vitro embryos (remaining portion of in vitro blastocysts after splitting some of the tec) were (94.4±5.6)% and (90.5±6.6)%. However, the culture development rate of half of the in vivo embryo (the remaining part of the embryo after splitting half of the embryo from the in vivo blastocyst) was significantly reduced to (22.2±14.7)%. 2) The success rate of DNA amplification in the half in vivo embryo group and the in vitro 2-cell group were 100%, while the success rates of DNA amplification in the in vivo TE group, the in vitro TE group and the in vitro 8-cell embryo group were (94.4±5.6)%, (76.2±9.5)% and (60.0±24.5)%, respectively. Compared with the half in vivo embryo group, the amount of DNA after WGA was significantly lower in both of in vivo TE group and in vitro TE group (P<0.05), and the amount of DNA after WGA was significantly lower in the in vitro TE group than that in the in vivo TE group (P<0.05). 3) Compared to the half vivo embryo group (91.2±1.6)%, the chip call rates were significantly lower in the in vivo TE group (76.7±15.2)%, in vitro TE group (74.3±9.6)%, in vitro 2-cell group (76.1±6.9)%, and in vitro 8-cell group (61.2±19.0)% (P<0.05), and the call rates were all lower than 90%. The in vitro 8-cell group had the lowest chip call rate compared to the other groups. 4) If at least 7 consecutive SNPs deletions were considered as the chromosome fragment deletion selection criteria, a total of 188 and 388 chromosome deletion fragments were obtained in the in vitro TE group and in vivo TE group, respectively. Gene selection identified that a total of 46 genes were included in the deletion fragments of the in vitro TE group and 48 genes were included in the deletion fragments of the in vivo TE group. GO and KEGG enrichment analysis showed that the differentially deleted genes in the in vitro TE group were significantly enriched to cytoskeleton and cell differentiation, whereas the genes enriched in the in vivo TE group were mainly related to cellular material secretion and transport. 5) The filling accuracy (R²) of 52 334 SNPs filling sites out of 64 958 SNPs filling sites was between 0.99 and 1, and the mean value of R² for all filling sites was 91%, indicating a high filling accuracy. Breeding value estimation showed that the production performance of in vitro TE group was lower than that of in vivo TE group. Together, using of embryo splitting, WGA and SNP chips can enable to assess the chromosome quality and production performance of early preimplantation embryos with little impact on the quality of embryo development;In addition, the abnormal expression of genes such as cytoskeleton during in vitro development may contribute to the poor quality of in vitro embryos.

Key words: bovine embryos, embryo splitting, single-cell amplification, SNP chips, embryo quality