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Aim of this study was to evaluate the effect of presence or absence of cumulus cells around oocytes, on post-vitrification survival rate, maturation and developmental capacity of bovine oocytes. Ovaries were collected from abattoirs and all visible follicles were aspirated and examined. Only, cumulus cell complex (COCs) and natural (NDOs) or mechanically denuded (MDOs) were vitrified/warmed, matured, fertilized and cultured for 7 days to calculate post-thawing survival, maturation, fertilization and blastocyst production rates. Results showed that the proportions of total and morphological normal oocytes recovered post-vitrification were greater (P<0.05) for COCs (79.0 and 76.0%) than those obtained for NDOs (56.0 and 51.4%). Also, post-vitrification recovery rate and proportion of morphological normal oocytes was greater (P<0.05) for MDOs (67.8 and 63.2%) than those for NDOs (56.0 and 51.4%). Proportion of damaged oocytes post-vitrification was not affected significantly by oocyte type, but leakage of cellular contents represented the highest frequency of damaged oocytes, while splitting in two halves was the lowest frequent abnormality observed. The COCs yielded the highest (P<0.05) percentages of oocytes at M II (maturation rate) and the lowest percentages of degenerated oocytes, followed by MDOs, while NDOs showed the lowest percentages, being 60; 10% for COCs, 46.9; 20.5% for MDOs and 38.9; 30.4% for NDOs, respectively. Cleavage rate was higher (P<0.05) for COCs than those of MDOs and NDOs (40.0 vs. 26.3 and 21.3%, respectively). Production rate of embryos at morula and blastocyst stages was not affected significantly by oocyte type. In conclusion, cumulus cell layer surrounding the bovine oocytes recovered from ovaries collected from abattoirs play very important roles for maintain viability of oocytes during vitrification, and successfully in vitro matured, fertilized and developed to blastocyst stage.

VITRIFICATION AND IN VITRO MATURATION AND FERTILIZATION OF BOVINE OOCYTES WITH OR WITHOUT CUMULUS CELL LAYER.