Porcine blastocyst viability and developmental potential is maintained for 48 h of liquid storage at 25 °C without CO2 gassing

Abstract

Short- and medium-term storage of pig embryos has become relevant for commercial application of non-surgical deep uterine embryo transfer (NsDU-ET) in the light of the strict legal and administrative requirements posed by the International Association for Air Transport (IATA) to allow shipment of liquid nitrogen (LN2) containers and the technical drawbacks when using vitrified embryos. Therefore, this study developed an efficient method for the liquid storage of in vivo-derived porcine blastocysts for a moderate duration (48 h) without controlled CO2 gassing. We evaluated two storage temperatures (25 °C and 37 °C) and three HEPES-supplemented media: the chemically defined media TL-PVA and NCSU-PVA and the semi-defined medium NCSU-BSA. We observed no differences in survival, hatching rate or final developmental stage between the two temperatures, but storage at 25 °C was more efficient to preserve zona pellucida (ZP) integrity. Blastocysts were successfully stored for 24 h in a chemically defined medium. Yet, only 48 h storage in NCSU-BSA medium supported blastocyst development. Although all storage conditions resulted in an embryonic developmental delay, blastocysts stored in NCSU-BSA at either tested temperature could hatch and attain the same final developmental stage as control blastocysts when cultured under standard conditions after storage. Moreover, blastocysts stored at 25 °C for 48 h in NCSU-BSA medium could produce pregnancies after surgical transfer. In conclusion, porcine blastocysts maintain their viability and developmental potential after storage in the semi-defined medium NCSU-BSA for at least 48 h at 25 °C.