En 1680-6433 2008-2177 Fusion and development of 2-cell bovine embryos to tetraploid blastocyst with different voltages and durations Background: The values of embryonic stem cell and cloning are evident. Production of clone from embryonic stem cells can be achieved by introduction of stem cell into a tetraploid blastocyst. Tetraploid blastocyst can be produced in vitro by electrofusion of 2-cell embryos. Objective: The aim of this study was to assess the effect of different voltages and durations on fusion rate of bovine 2-cell embryos and their subsequent development in vitro. Material and Methods: The in vitro produced bovine 2-cell embryos were categorized into 3 groups: (1) fused group (FG); 2-cell embryos fused by exposure to different voltages (0.5, 0.75, 1, 1.25 and 1.5 kV/cm) and durations (20, 40, 60, 80 and 100 μs), (2) exposed control group (ECG); 2-cell embryos exposed to different voltages and durations but remained unfused and (3) unexposed control group (UCG); embryos cultured without exposure to any voltage. The embryos from each group were cultured and fusion, cleavage and developmental rates were compared in each group. Results: The results show that increased voltage, increases the fusion rate up to 88% for 1.5 kV/cm; however, the rate of cleavage and blastocyst formation decreases significantly to 18% and 10% respectively (p<0.05). Increased duration does not significantly increase fusion rate, however, in high voltage, increased duration decreases cleavage rate and blastocyst formation rate. Blastocyst formation rate in UCG showed a better development (32%) compared to FG (20%) or ECG (22.5%) (p<0.05). Conclusion: It can be concluded that for optimal fusion, cleavage and development, one pulse of 0.75 kV/cm for 60μs should be applied. Background: The values of embryonic stem cell and cloning are evident. Production of clone from embryonic stem cells can be achieved by introduction of stem cell into a tetraploid blastocyst. Tetraploid blastocyst can be produced in vitro by electrofusion of 2-cell embryos. Objective: The aim of this study was to assess the effect of different voltages and durations on fusion rate of bovine 2-cell embryos and their subsequent development in vitro. Material and Methods: The in vitro produced bovine 2-cell embryos were categorized into 3 groups: (1) fused group (FG); 2-cell embryos fused by exposure to different voltages (0.5, 0.75, 1, 1.25 and 1.5 kV/cm) and durations (20, 40, 60, 80 and 100 μs), (2) exposed control group (ECG); 2-cell embryos exposed to different voltages and durations but remained unfused and (3) unexposed control group (UCG); embryos cultured without exposure to any voltage. The embryos from each group were cultured and fusion, cleavage and developmental rates were compared in each group. Results: The results show that increased voltage, increases the fusion rate up to 88% for 1.5 kV/cm; however, the rate of cleavage and blastocyst formation decreases significantly to 18% and 10% respectively (p<0.05). Increased duration does not significantly increase fusion rate, however, in high voltage, increased duration decreases cleavage rate and blastocyst formation rate. Blastocyst formation rate in UCG showed a better development (32%) compared to FG (20%) or ECG (22.5%) (p<0.05). Conclusion: It can be concluded that for optimal fusion, cleavage and development, one pulse of 0.75 kV/cm for 60μs should be applied. Bovine, Embryo, Development, Electrofusion, Tetraploid. Bovine, Embryo, Development, Electrofusion, Tetraploid. 181 186 Mohamad Reza Darabi Mohamad Reza Darabi - No Mohamad Hosein Nasr-Esfahani Mohamad Hosein Nasr-Esfahani mh.nasr-esfahani@royaninstitute.org No