Apoptosis in porcine cumulus-oocyte complexes: Relationship with their morphology and the developmental competence

The aim of this study was to assess the presence and distribution of apoptosis in porcine cumulus-oocyte complexes (COCs) and its relations with COC morphology and developmental competence. The COCs were obtained from slaughterhouse ovaries, classified into A1 (top category), A2, B1, B2, C, and D based on their morphology. A1, A2, and B1 were matured and fertilized in vitro, and blastocyst rate was compared among them. Before and after in vitro maturation (IVM), annexin-V staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays were performed to assess early and late apoptosis, respectively. There was a significant increase in both annexin-V (+) oocytes and TUNEL (+) cumulus cells as morphology further deteriorated. There were no statistical differences regarding annexin-V (+) oocytes within immature and post-IVM COCs, but TUNEL (+) oocytes were only observed in post-IVM COCs. Early and late apoptosis was detected in cumulus cells of all categories of immature and post-IVM COCs. However, the difference was only significant for annexin-V (+). There were no significant differences in embryo development. Therefore, apoptosis increases as the morphological features of the immature COCs decrease. In conclusion, the selection of COCs from Categories A1, A2, and B1 may be used as a selection criterion for in vitro development.