Relationship Between Morphology Of Bovine COCs And Their Developmental Potential And Apoptosis

A morphological classification of the immature cumulus-oocyte complex(COC)was used to determine the developmental potential of bovine oocytes. The COCs,according to their cumulus and ooplasm features, were classified into fourcategories, designated as follows: COCs with heterogeneous ooplasm with dark clustersand much more layered cumulus investment as categoryⅠ; COCs with homogeneousooplasm and much more layered cumulus investment as categoryⅡ; COCs withheterogeneous ooplasm with dark clusters and few layered cumulus investment ascategoryⅢ; COCs with homogeneous ooplasm and few layered cumulus investment ascategoryⅣ. FOR the four categories the nuclear status was evaluated by orcein stainingand the developmental competence was evaluated by in vitro fertilization. The resultsfrom this research are as follows:The rates of the four categories oocytes in MⅡafter 22 hours maturation were71.30%,39.00%,78.10% and 64.82%, the rates of ova Cleavage were 72.64%, 47.88%,87.30%, 79.25%,the rates of 8-cell stage were 57.18%,19.91%,68.48% and 49.87%, therates of blastocysts were 32.30%, 10.80%, 47.56% and 31.36%, the rates of hatchedblastocysts were 9.10%,2.27%,26.71% and 8.90%, respectively. Statistically significantless were found in the rates of MⅡ, Cleavage,8-cell stage and blastocysts compared categoryⅡwith other three categories, respectively (P＜0.01). Statistically significantmore were found in the rates of hatched blastocysts compared categoryⅢwith otherthree categories (P＜0.01). Results showed that the categoryⅢhad the highestⅣEP(invitro embryos production)potential and categoryⅡhad the lowestⅣEP potential. Itdemonstrated that the considered morphological criteria for COCs classification wererelated to developmental competence in bovine oocytes.The morphological analysis of nuclear changes with an assessment of chromatinfragmentation by terninal deoxynucleotidyl transferase-mediated dUTP nick end-labeling(TUNEL) assay, a way to detect DNA fragmentation, was carried out to investigate onbovine oocytes developmental competence and resultant incidences of nuclear DNAfragmentation as an indication of oocytes quality. Immature oocytes, matured after 22hours and 72 hours oocytes were subjected to apoptosis analysis by TUNEL assay. Theresults suggested that no apoptosis was detected in immature or matured after 22hoursoocytes, and the occurrence of apoptosis in these oocytes are not related to developmentalcompetence. As the culture time goes by, the number of apoptosis oocytes is increasing.