Abstract
This study aimed to evaluate the effect of different cryodevices [conventional straws (CS) and open pulled straws (OPS)] of vitrification on viability, morphology and ultrastructure of ovine immature oocytes. Ovaries of slaughtered ewes were transported from a local abattoir to our laboratory in 0.9 % normal saline at 25–30 °C. The visible follicles (1–6 mm in diameter) were sliced with a microblade and their cumulus-oocyte complexes (COCs) were released in Dulbecco’s phosphate buffer saline. Upon examination under a stereomicroscope, good quality oocytes (n = 266) were selected and randomly assigned into three groups: 1) Fresh oocytes (control, n = 78); 2) Oocytes vitrified using CS (n = 95) and 3) Oocytes vitrified using OPS (n = 93). The gross morphology of COCs was evaluated under a stereomicroscope whilst their viability was evaluated in Trypan blue stained smear. Moreover, glutaraldehyde-fixed COCs (n = 45) were processed for transmission electron microscopy. It was observed that the proportion of recovered normal ovine oocytes after vitrification in OPS (89.24 %) was significantly higher (P < 0.05) than those vitrified in CS (73.68 %). Meanwhile, the proportion of abnormal oocytes was greater (16.84 %) in CS than OPS (8.60 %). The proportion of viable ooplasm and viable cumulus oocytes was significantly (P < 0.05) higher in the fresh group (88.88 %) than OPS (69.11 %) and CS (54.54 %) groups with significant (P < 0.05) difference between the two vitrification groups. Notably, ultrastructural alterations of vesicles and lipid droplets in fresh oocytes were similar with OPS and lower than CS vitrified-warmed oocytes without significant difference between the two vitrified groups. In conclusion, OPS vitrified-warmed oocytes have less cryoinjuries and higher survivability in comparison with CS vitrified-warmed oocytes, although ovine immature oocytes were more vulnerable to cryopreservation by vitrification.
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