DEVELOPMENT IN-VITRO OF RABBIT EMBRYOS AFTER FREEZING BY 2-STEP OR ULTRARAPID COOLING METHODS

The effects of rapid freezing by two-step and ultrarapid cooling metho ds on 2-cell, 8 to 16-cell, compacted morula and early blastocyst stag es of rabbit embryos were examined. Dimethylsulfoxide (DMSO, 3.5 mol/l ) combined with sucrose (0.25 mol/l) was used as the freezing medium. The embryos were loaded into plastic straws with the freezing medium, held during 2.5 min and then were directly plunged into liquid nitroge n (ultrarapid cooling) or after a time from 30 to 45 min held at -27 d egrees C (two-step cooling). After rapid thawing embryo development wa s evaluated by in vitro developmental capacity shown by the embryos an d was compared to control. All studied embryonic stages developed in v itro after two-step and ultrarapid cooling procedures. However, higher developmental rates were obtained when the two-step cooling method wa s used. Using the two-step cooling method, best results were obtained at compacted morula and blastocyst stages, and no significant differen ces were shown when compared with control embryos at blastocyst stage. All embryonic stages to which the ultrarapid cooling method was appli ed showed lower developmental rates than control. The results show tha t a high proportion of rabbit embryos can develop in vitro after freez ing by two-step cooling method.