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The present study in rabbits compared, in the first experiment, the effect of two commonly used oocyte ages, 13 h and 17 h after ovulation induction treatment, on the technical efficiency of somatic nuclear transfer steps, using fresh cumulus cells as nuclear donors. Recently ovulated metaphase II oocytes (13 h) showed higher fusion (13 h: 83% vs 17 h: 67%, p < 0.05) and in vitro development rates than in vivo slightly aged metaphase II oocytes (morula, 13 h: 74% vs 17 h: 25%, p < 0.05; blastocyst, 13 h: 16% vs 17 h: 8%; p < 0.05). In contrast, activation rate was higher in the 17 h group (13 h: 45% vs 17 h: 67%; p < 0.05). In a second experiment, using recently ovulated oocytes (13 h) as recipients, two donor cell types (from primary cultures of either cumulus cells or fetal fibroblasts) were tested to evaluate their effects on the efficiencies of the different technical steps of somatic nuclear transfer procedure. A better fusion rate was obtained when fetal fibroblasts were used as nuclear donors (cumulus cells: 45% vs fetal fibroblasts: 67%, p < 0.05). No statistically significant differences were detected in cleavage rate regardless of the cell type used (cumulus cells: 44% vs fetal fibroblasts: 60%, p > 0.05). However, in vitro development to morula (cumulus cells: 41% vs fetal fibroblasts: 14%, p < 0.05) and to blastocyst stage (cumulus cells: 27% vs fetal fibroblasts: 3%, p < 0.05) were different between cell types.

These result demonstrate that denuded expanded or hatching rabbit blastocysts of greater size can be satisfactorily vitrified by use of a two-step procedure. The similarity of vitrification solutions used in humans could make it feasible to test such a procedure on human denuded blastocysts of different sizes.