Ultrastructure of in vitro matured bovine oocytes after controlled freezing in 10% glycerol

The purpose of this study was to investigate the developmental capacity of, and possible subcellular damage to, bovine oocytes upon freezing and thawing. Following in vitro maturation, bovine oocytes were dehydrated in 10% glycerol, frozen, thawed, rehydrated, inseminated and further cultured in vitro. The cleavage rate among control ova was 74% versus only 3% among their frozen counterparts. In the control group 45% developed to blastocysts, whereas no blastocysts were obtained with frozen/thawed oocytes. s were collected before freezing, after dehydration, cooling to −5°C, seeding/thawing/rehydration and after freezing/thawing/rehydration and were prepared for transmission electron microscopy. seeded/thawed oocytes the vesicles of the ooplasm were peripherally dislocated and displayed some degree of confluence and variation in size. The frozen/thawed oocytes exhibited a high degree of heterogeneity in vesicle size and even more vesicles had become confluent. The smooth endoplasmic reticulum (SER) and mitochondria displayed pronounced dilation. Again, the vesicles were peripherally dislocated, and in more than half of the oocytes the oolemma was ruptured and the perivitelline space was occupied by ooplasmic content. concluded that cryopreservation of in vitro matured bovine oocytes is associated with ultrastructural damages, which become evident after seeding and especially the subsequent freezing and which deprive the oocyte of its developmental capacity.