Generally, blastocyst (BL) formation and embryo cell number are used as main parameters to evaluate the viability and quality of in vitro-produced somatic cell nuclear transfer (SCNT) embryos. We investigated whether in vitro development of SCNT pig embryos correlates with in vivo viability after transfer to surrogates. For SCNT, cumulus–oocyte complexes (COCs) were matured in TCM-199 supplemented with follicular fluid, hormones, EGF, cysteine, and insulin for the first 22 h and in a hormone-free medium for 18 h. Three sources of pig skin cells were used as nuclear donor: (1) skin fibroblasts of a cloned piglet that were produced by SCNT of fetal fibroblasts from a Landrace × Yorkshire × Duroc F1 hybrid (LYD), (2) skin fibroblasts of a miniature pig having the human decay accelerating factor gene (hDAF-MP), and (3) skin fibroblasts of a miniature pig with a different strain (MP). MII oocytes were enucleated, subjected to nuclear transfer from a donor cell, electrically fused, and activated 1 h after fusion. SCNT embryos were cultured in a modified NCSU-23 (Park Y et al. 2005 Zygote 13, 269–275) for 6 days or surgically transferred (110–150 fused embryos) into the oviduct of a surrogate that showed standing estrus on the same day as SCNT. Embryos were examined for cleavage and BL formation on Days 2 and 6, respectively (Day 0 = the day of SCNT). BLs were examined for their cell number after staining with Hoechst 33342. Pregnancy was diagnosed by ultrasound 30 and 60 days after embryo transfer. Embryo cleavage was not affected by donor cells (82, 81, and 72% for LYD, hDAF-MP, and MP, respectively), but BL formation was higher (P < 0.05) in hDAF-MP (16%) than in LYD (9%) and MP (6%). MP showed higher (P < 0.05) BL cell number (46 cells/BL) than hDAF-MP (34 cells) but did not show a difference from LYD (37 cells). LYD and MP showed higher pregnancy rates (Table 1) on Days 30 and 60, even though they showed lower BL formation in vitro. Due to a relatively small number of embryo transfers through a limited period, we could not exclude any possible effects by seasonal or operational differences. These results indicated that pregnancy did not correlate with in vitro BL formation of SCNT pig embryos but rather were affected by the source of donor cells.

This work was supported by the Research Project on the Production of Bio-organs (No. 200506020601), Ministry of Agriculture and Forestry, Republic of Korea.