Cryotop and Solid Surface Vitrification Cryodevices are Suitable for the Cryopreservation of In Vitro-Matured Water Buffalo (Bubalus bubalis L.) Oocytes

This work was conducted to evaluate the efficiency of Cryotop (CTP) and Solid Surface Vitrification (SSV) cryodevices in cryopreserving in vitro-matured buffalo oocytes and to study the influence of cumulus cells on viability of vitrified oocytes. Cumulus cell-free and -enclosed oocytes were exposed to an equilibration solution (ES) consisting of 7.5% (v/v) ethylene glycol (EG) and 7.5% (v/v) DMSO in TCM 199 + 20% FCS (base medium), for 5 min and then to a vitrification solution (VS) consisting of 15% (v/v) EG and 15% (v/v) DMSO with 0.5 M sucrose for 40 sec. The oocytes were then cooled in liquid nitrogen (LN2) using either a metal surface for SSV or Cyrotop sheets. Warming was performed in base medium with 1.0 and 0.5 M sucrose solutions, respectively. In experiment I, buffalo oocytes were exposed only to ES and VS for chemical toxicity. No significant differences were observed in cleavage, development to morula and blastocyst between the solution-exposed and unexposed groups. The cumulus cell-enclosed oocytes however, yielded significantly higher developments than cumulus cell-free oocytes after IVF. In Experiment II, oocytes were exposed to ES and VS and cooled in LN2. In vitro developments of cumulus cell-enclosed oocytes were not significantly different between SSV and Cryotop cryodevices. The present study demonstrated that buffalo MII oocytes can be cryopreserved successfully using CTP or SSV cryodevices with similar efficiencies and that the presence of cumulus cells was beneficial for their in vitro development. Key words: cryodevices, Cryotop, in vitro matured buffalo oocytes, minimum-volume cooling, solid surface vitrification