Chromosome aberrations in in vitro-produced bovine embryos at days 2-5 post-insemination

Availability of embryos of high quality is required to obtain satisfactory embryonic developmental rates and normal calves following transfer of in vi tro-produced (IVP) bovine embryos. One relevant quality parameter is the fr equency of chromosome aberrations, which can be evaluated using multicolor fluorescent in situ hybridization (FISH) with chromosome 6- and chromosome 7-specific probes in cattle. In this study, interphase nuclei (n = 3805) we re analyzed from 426 bovine IVP embryos. We found that 73%, 72%, 81%, and 5 8% of the embryos from Days 2, 3, 4, and 5 post-insemination (pi), respecti vely, displayed a normal diploid chromosome number in all cells. When looki ng at the types of chromosome aberrations, the percentages of mixoploidy at Days 2, 3, 4, and 5 pi were 22%, 15%, 16%, and 42%, respectively, whereas the percentages of polyploidy (i.e., all nuclei in an embryo were analyzed and were polyploid) were 5%, 13%, 3%, and 0%, respectively. In conclusion, numerical chromosome aberrations were detected as early as Day 2 pi. The de velopment of polyploid embryos is slow and is apparently arrested during th e third cell cycle, whereas the mix-oploid embryos seem to continue develop ment.