SURVIVAL RATE OF IMMATURE AND IN VITRO MATURED BOVINE OOCYTES VITRIFIED USING CRYOLOOP METHOD
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Date
2016-07-05
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COLLEGE OF VETERINARY AND ANIMAL SCIENCE-MANNUTHY,THRISSUR
Abstract
Successful cryopreservation of oocyte using vitrification ensures the
availability of large number of oocytes for in vitro maturation (IVM) and in vitro
fertilization (IVF). The present study was carried out to evaluate effect of meiotic
stage on survival rate of bovine oocytes after cryoloop vitrification and to assess
viability using morphological evaluation and trypan blue staining.
Ovaries of 36 slaughtered cattle were selected and randomly allotted to three
groups. Oocytes were recovered by follicular aspiration. Half of the group І culture
grade oocytes (n=44) were subjected to trypan blue (0.05%) staining for viability
assessment and aceto-orcein staining for evaluation of nuclear status. Culture grade
oocytes in group ІІ (n=38) were matured in vitro after cryoloop vitrification and
culture grade oocytes in group ІІІ (n=39) were vitrified after in vitro maturation.
A total of 241 oocytes were aspirated and yield of immature oocytes per cow
was 6.69. Trypan blue staining of culture grade oocytes obtained by morphological
evaluation in group І yielded only 81.82 per cent live oocytes. Aceto-orcein staining
of group І culture grade oocytes revealed that 54.44 per cent of oocytes were in GV
stage.
Morphological survival rate of mature vitrified oocytes in group ІІІ was
higher than immature vitrified and matured oocytes in group ІІ (66.67% vs 52.63%).
Cumulus expansion, polar body extrusion and trypan blue dye exclusion rate were
also higher in group ІІІ, whereas nuclear maturation rate was almost similar.
The meiotic stage at which cryoloop vitrification was carried out had no
significant influence on survival rate, viability, cumulus expansion, polar body
extrusion and nuclear maturation rate of bovine oocytes. Hence immature bovine
oocytes can be preserved using cryoloop technique, where facilities are not available
for IVM. Compared to morphological evaluation, trypan blue staining technique was
found to be more reliable for assessing oocyte viability.
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