Pig embryonic stem cells (ESC) has been suggested to become important animal model for therapeutic cloning using embryonic stem cells derived by somatic cell nuclear transfer (SCNT). However, the quality of cloned embryo and derivation rate of cloned blastocyst has been presented limits for derivation of cloned embryonic stem cell. In this study, we have tried to overcome these problems by aggregating porcine embryos. Zonafree reconstructed SCNT Embryos were cultured in micro-wells singularly (non-aggregated group) or as aggregates of three (aggregated groups) at the four cell stage. Embryo quality of the cloned embryos and attachment on feeder layer rate significantly increased in the aggregates. The aggregation of pig SCNT embryos at the four-cell stage can be a useful technique for improving the quality of pig cloned blastocyst and improvement in the percentage of attachment on the feeder layer of cloned embryos. * This work was supported by the BioGreen 21 Program (PJ0081382011), Rural Development Administration, Republic of Korea.

• Dong-Kyung Lee(Department of Agricultural Biotechnology, Animal Biotechnology Major, and Research Institute for Agriculture and Life Science, Seoul National University, Seoul, Korea)
• Jae-Yeon Hwang(Department of Agricultural Biotechnology, Animal Biotechnology Major, and Research Institute for Agriculture and Life Science, Seoul National University, Seoul, Korea)
• Jong-Nam Oh(Department of Agricultural Biotechnology, Animal Biotechnology Major, and Research Institute for Agriculture and Life Science, Seoul National University, Seoul, Korea)
• Chang-Kyu Lee(Department of Agricultural Biotechnology, Animal Biotechnology Major, and Research Institute for Agriculture and Life Science, Seoul National University, Seoul, Korea)