Comparison of different cryoprotectant regimes for vitrification of ovine embryos produced in vivo

This study was aimed to compare different cryoprotectants for vitrification of sheep embryos produced in vivo. Blastocysts were obtained from superovulated Santa Ines ewes and randomized into three groups: conventional freezing using ethylene glycol (EG) (control group), vitrification with EG and dimethyl sulfoxide (DMSO vitrification), or vitrification with EG and dimethylformamide (DMF vitrification). All groups were analyzed for embryonic viability (propidium iodide staining), re-expansion rate after thawing (at morphological and ultrastructural levels) and pregnancy rate after embryo transfer (ET). Embryos of DMSO vitrification group showed lower cell viability (44.44%), compared to DMF group and control embryos (77.77% and 100%, respectively). The ultrastructural study showed similar cryopreservation damage among control and DMF embryos, and these were less damaged than DMSO vitrified embryos. Embryos vitrified with DMF had higher rates of re-expansion in vitro (53.33%) than DMSO (26.66%), and control (33.33%). After ET, similar pregnancy rates were obtained from all groups (DMF: 45%, DMSO: 30%, control: 40%). Collectively, DMF vitrification is more efficient than DMSO vitrification and is indistinguishable from conventional freezing of sheep embryos.