Metal mesh vitrification (MMV) method for cryopreservation of porcine embryos

The objective was to develop a simpler, more reliable vitrification method for porcine embryos. Prepubertal donor gilts were induced to ovulate with eCG and hCG, and then inseminated artificially. Morulae and expanding blastocysts approximately 200 μm in diameter were collected 6 or 7 d after hCG treatment. Embryos collected from donor gilts were maintained, so as to be individually recognizable, and handled in batches of four or five. The embryos together with a minimum volume (<2 μL) of vitrification solution were placed onto stainless steel metal meshes or plastic plates, and then plunged into liquid nitrogen—metal mesh vitrification (MMV) and plastic plate vitrification (PPV), respectively. The meshes or plates were stored in 1.8-mL cryotubes submerged in liquid nitrogen. Stored embryos were subsequently removed, cultured in medium for 24 h, and then assessed for viability. The survival rate (84.4%) of expanding blastocysts cooled by MMV was higher than that (53.1%) of embryos cooled by PPV (P < 0.05). There was no significant difference in total cell number between MMV and PPV. The survival rate of morulae cooled by MMV was 55.0%. Transfer of 200 expanding blastocysts cooled by MMV to 10 synchronized recipient gilts resulted in 37 live piglets from 7 recipients. In conclusion, the MMV method was an effective vitrification procedure for cryopreservation of expanding porcine blastocysts. However, there was a batch effect on embryo survival after vitrification.