Sex Determination by Polymerase Chain Reaction and Karyotyping of Bovine Embryos at First Cleavage in vitro

The purpose of this study was to compare the embryo sexing methods between PCR and karyotyping of in vitro produced (IVP) bovine embryos at the 2-cell stage. The embryos were divided into 3 groups according to the time of first cleavage completion. Zygotes cleaving before 24 hours postinsemination (hpi), during 24-36 hpi and after 36 hpi were classified as fast, intermediate and slow cleaving embryos, respectively. All 2-cell stage bovine embryos were separated into two blastomeres, one was karyotyped and the other was subjected to PCR amplification. The percentages of embryos which were sexed by PCR were significantly (p<0.005) higher than those analyzed by karyotyping (100% vs 56%). The proportions of male embryos sexed by PCR and karyotyping in the fast and intermediate cleaving groups were significantly (p<0.05) higher than female embryos, whereas the proportions of males were significantly (p<0.05) lower in the slow cleaving group. The overall ratios of males to females analyzed by both methods were significantly (p<0.05) different from the expected ratio of 1:1.