Effect of different shipping temperatures (∼22 °C vs. ∼7 °C) and holding media on blastocyst development after overnight holding of immature equine cumulus-oocyte complexes

Abstract Intracytoplasmic sperm injection (ICSI) is an important tool for equine embryo production in both clinical and research settings. In clinical ICSI programs, immature equine cumulus-oocyte complexes (COCs) are often collected at the mare's location and shipped to the ICSI laboratory. To simplify shipment and aid scheduling of subsequent procedures, COCs can be held overnight at room temperature (∼22 °C) before placement into maturation culture, with no detrimental effect on meiotic or developmental competence. A recent study indicated that it might be possible to hold COCs overnight at cold (∼4 °C) temperatures. If so, this might allow longer holding periods that would ease shipping requirements. In this study, we compared oocyte maturation rates, as well as cleavage and blastocyst rates after ICSI, for COCs held at either room or cold temperatures overnight before the onset of in vitro maturation. In Exp. 1, COCs were shipped overnight in a commercial embryo holding medium, ViGRO (Vg), in insulated containers designed to hold at either room temperature (RT, ∼22 °C) or cold temperatures (Cold, ∼7 °C). Subsequent rates of in vitro maturation, cleavage and blastocyst formation were significantly higher in the RT treatment (39%, 90% and 41%, respectively) than in the Cold treatment (23%, 60% and 17%, respectively, P P