Chromosomal abnormalities in bovine embryos and their influence on development

A study was undertaken to determine the relationship between chromosome composition and embryo development. Bovine cumulus-oocyte complexes were matured in vitro and exposed to semen from one of three different bulls, one of which was a 1/29 Robertsonian translocation carrier. There were no significant differences among the three bulls in their sperm penetration or in the cleavage or developmental rates of resulting embryos, which were subjected to chromosome analysis on Day 2 (40-44 h postinsemination [hpi]) and Day 5 (120-124 hpi) of development. No difference was detectable in the growth rates of embryos of different chromosomal composition on Day 2. On Day 5, a total of 343 embryos were obtained from all three bulls, of which 158 embryos could be karyotyped and assessed for cell numbers. Cell numbers for the Day 5 embryos showed that the mean numbers for the individual chromosome compositions (least-squares means +/- SEM) were 7.9 +/- 6.0 for haploids, 7.9 +/- 6.0 for polyploids, 16.8 +/- 4.3 for aneuploids, 23.4 +/- 4.0 for mixoploids, and 30.0 +/- 1.7 for diploids, indicating a significant reduction in the growth rate of embryos with chromosomal abnormalities (p < 0.001). It was concluded that development rates (as evidenced by cell numbers) were slowest in haploid and polyploid embryos, intermediate in aneuploid embryos, and fastest in mixoploid and diploid embryos.