EFFECTS OF CUMULUS CELLS, DIFFERENT CRYOPROTECTANTS, VARIOUS MATURATION STAGES AND PREINCUBATION BEFORE INSEMINATION ON DEVELOPMENTAL CAPACITY OF FROZEN-THAWED BOVINE OOCYTES

To improve freezability of bovine follicular oocytes, it is necessary to minimize injury to the oocytes caused by freezing and the toxicity of cryoprotectants. The maturing ability of frozen-thawed follicular o ocytes with or without cumulus complexes was tested. The proportion of frozen-thawed follicular oocytes reaching the metaphase II (M II) sta ge after in vitro maturation of 24 h was significantly (P<0.05) higher in cumulus oocyte complexes (COCs; 44%) than in denuded oocytes (30%) . Oocytes were cultured for 0, 6, 12, 18 or 24 h then frozen-thawed wi th 1,2-propanediol (FROH) or dimethyl sulfoxide (DMSO), and cultured f or 24, 18, 12, 6 or 0 h respectively. In PROH, 24:0 (67%) showed signi ficantly (P<0.05) higher maturation rate than 0:24 (38%), 6:18 (41%). In DMSO, 18:6 (72%) and 24:0 (61%):showed significantly (P<0.05) highe r maturation rate than 0:24 (30%), 6:18 (33%) and 12:12 (44%). In case of 18:6, DMSO (72%) showed significant (P<0.05) higher maturation rat e than FROII (52%), however in case of 0:21, 6:18, 12:12 and 24:0, the re-was no significant (P<0.05) difference in the maturation rate betwe en PROH and DMSO. The proportion of embryos developed to greater than or equal to 2cell, greater than or equal to 8cell, morula and blastocy st in 18:6 DMSO (35, 10, 3 and 0%) and 24:0 PROH (38, 12, 5 and 0%) wa s significantly (P<0.05)lower than that of fresh oocytes (67, 38, 31 a nd 16%). There was no significant (P<0.05) difference in the rate of e mbryos that developed to greater than or equal to 2cells, greater than or equal to 8cells, morulae and blastocysts between PROII and DMSO. W hen the frozen oocytes were grouped as rewarming culture (21:2 PROII) and control (24:0 PROH), there was no significant (P<0.05) difference in the rate of embryos that developed to greater than or equal to 2cel ls, greater than or equal to 8cells, morulae and blastocysts between 2 4:0 PROII (42, 24, 11 and 1%) and 21:2 PROH (51, 29, 16 and 4%) but 21 :2 PROH showed slightly higher developmental capacity than 24:0 PROH. Transferable blastocysts (4%) were obtained in 21:2 PROH when the froz en-thawed follicular oocytes were fertilized and cultured for 8 to 9d. (C) 1997 by Elsevier Science Inc.