Development of in vitro matured bovine oocytes after cryopreservation withdifferent cryoprotectants

In vitro matured bovine oocytes at the metaphase-II stage were slowly froze n in phosphate buffered saline (PBS) containing 1.0 M glycerol, 1.0 M dimet hylsulfoxide (DMSO) or 1.0 M propylene glycol (PROH). When thawed rapidly, more (P<0.05) oocytes were morphologically normal after being frozen with D MSO (86%) or PROH (83%) than with glycerol (62%). When inseminated in vitro with frozen-thawed bull spermatozoa, higher (P<0.05) penetration rates wer e observed in DMSO (79%) or PROH (76%) than in glycerol (48%). The percenta ges of oocytes developing to the 2-cell stage at 48 h postinsemination were also significantly (P<0.05) higher in DMSO (51%) and PROH (54%) than in gl ycerol (33%). However, a significant increase in the proportions of 8-cell embryos (46 vs 21 to 26%; P<0.05) at 72 h postinsemination and morulae (14 vs 6 to 8%; P<0.05) was derived from oocytes frozen with PROH than with DMS O or glycerol. In conclusion, the type of cryoprotectant used is one of the critical factors affecting developmental competence of bovine oocytes froz en at the metaphase-II stage. For this stage of oocytes, PROH was the most effective, yielding a large number of 8-cell embryos and morulae than eithe r glycerol or DMSO in a slow freezing method combined with a 3-step thawing protocol. (C) 1999 by Elsevier Science Inc.