Abstract
A simplified procedure for bisection of bovine morulae and blastocysts involving a fine microsurgical blade and Dulbecco's phosphate-buffered saline (PBS) supplemented with 0.3 M sucrose and 0.1 mM ethylene diamine tetra acetic acid (EDTA) was employed to examine the developmental ability of the bisected demi-embryos. This procedure did not require a holding pipet to restrain the embryo and only a single micromanipulator was needed. Bisected embryos were transferred to recipient heifers either as pairs of demi-embryos or as single demi-embryo to compare maintenance of pregnancy and fetal survival as to the incidence of identical twins. Blastocyst formation rate was significantly (P<0.05) higher (78.3% vs 60.5%) in embryos bisected in medium containing sucrose as compared to controls when early or mid-blastocyst stage embryos were bisected. Bilateral transfer of bovine demi-embryos generated more fetuses per original embryo than unilateral transfer of a single demi-embryo (105% vs 93%). Embryos producing identical twin pregnancies from sets of demi-embryos (bisected-twins) represented 30.7% of the total while 39.8% of embryos produced one pregnancy and the remaining 29.5% failed to result in pregnancy. The results show that bovine embryos can be bisected by a simplified method and lead to normal pregnancies with a high incidence of identical twins.
