Morphological changes, DNA damage and developmental competence of in vitro matured, vitrified-thawed buffalo (Bubalus bubalis) oocytes: A comparative study of two cryoprotectants and two cryodevices

Present study was designed to investigate the impact of two cryodevices; french mini straw (FMS) and open pulled straw (OPS) using two different cryoprotectants; ethylene glycol (EG) and propylene glycol (PG) on morphological damage, recovery rate, DNA damage and developmental competence of in vitro matured vitrified-thawed buffalo oocytes. In vitro matured oocytes were divided into three groups: (a) no cryoprotectant (unfrozen, control), (b) vitrified in FMS and (c) in OPS using EG/PG. After thawing, recovered oocytes were subjected to morphological evaluation, cryoinjury at DNA level and their developmental competence. Results showed that recovery rate from both the groups (b and c) were almost same. Amongst the morphological damaged oocytes, zona pellucida crack, oocyte shrinkage and splitting were significantly (P < 0.05) higher in FMS with PG as compared to FMS with EG (group b) while, OPS with EG was significantly (P < 0.05) better as it maintained the architecture of oocytes and hardly any damage was found except some cytoplasmic shrinkage and change in shape. The number of oocytes displaying DNA damage was significantly (P < 0.05) higher in FMS with PG. Cleavage and blastocysts production rate was significantly higher (P < 0.05) for the oocytes recovered from OPS as compared to FMS with PG or EG. OPS with EG gave best cleavage and blastocysts rate amongst all the groups. In conclusion, combination of EG with OPS gives the best result in terms of better recovery and survival rate, least morphological damages with good developmental competence of vitrified matured buffalo oocytes post-thawing.