Holding temperature to transport immature bovine oocytes in collection media critically affects their developmental competence

We investigated the holding condition in collection media to establish transportation system of immature bovine cumulus-oocyte complexes (COCs). We examine holding temperature (38℃ or 20℃), basal media (Lactated Ringer's solution and TCM199) and supplementation of hypoxanthine, an inhibitor of meiotic resumption. As a result, no blastocyst was obtained from COCs held at 38℃ for 6 h or longer, whereas blastocysts were obtained even after 24 h holding in all experimental groups held at 20℃. The blastulation rate was maintained (42%) in TCM199 with hypoxanthine group even after 12 h holding, while reduction of the blastulation rates were observed in all other groups (P < 0.05). After 24 h of storage, Lactated Ringer's solution without hypoxanthine showed the highest blastulation rate (40%). In conclusion, holding temperature of oocytes critically affects the developmental competence of oocytes, and oocytes held at 20°C maintain their developmental competence at least 12 h.