Structural Changes in Cattle Immature Oocytes Subjected to Slow Freezing and Vitrification

This study was conducted to evaluate the effect of different cryopreservation methods (slow-freezing and vitrification) on structural changes of bovine immature oocytes. bovine ovaries were collected from local abattoirs. cumulus-oocytecomplexes (cocs) were retrieved using aspiration method from 2-6 mm follicles. in experiment 1, selected oocytes were randomly divided into 4 treatment groups namely freezing solution-exposed, frozen-thawed, vitrification solution-exposed and vitrified-thawed and then oocytes abnormalities were examined under a stereomicroscope. in experiment 2, oocytes were randomly allocated to the same grouping as experiment 1 plus control group. following freezing or vitrification, all oocytes were fixed in glutaraldehyde and processed for transmission electron microscopy. in experiment 1, there was a higher incidence of abnormalities in the frozen-thawed and vitrified-warmed oocytes compared to those in freezing solution and vitrification solution-exposed groups (p<0.05). in experiment 2, there were marked alterations in the perivitelline space, microvilli and vesicles of frozenthawed and vitrified-warmed oocytes characterized by loss of elasticity and integrityof cytoplasmic processes and microvilli following cooling and warming. in conclusion, ethylene glycol-based freezing and vitrification solutions are suitable choices for cryopreservation of immature oocytes and most organelles are able to retain their normal morphology following cryopreservation and thawing processes.