Developmental competence of porcine oocytes selected by brilliant cresyl blue and matured individually in a chemically defined culture medium

The objective of this study was to investigate the effects of oocyte selection using brilliant cresyl blue (BCB) and culture density during individual in vitro maturation (IVM) on porcine oocyte maturity and subsequent embryo development using a chemically defined medium. Cumulus-oocyte complexes (COCs) were classified as BCB-positive or BCB-negative after exposure to a BCB solution for 90 min. The classified COCs were matured in a group (15 COCs per 100-μL droplet) or individually (1 COC per 1-, 2.5-, 5-, or 10-μL droplet). Meiotic competence, intraoocyte glutathione concentration, and developmental competence after intracytoplasmic sperm injection were monitored. The BCB selected oocytes competent for nuclear and cytoplasmic maturation. Furthermore, meiotic competence for oocytes matured individually in a 5-μL droplet was superior (P < 0.05) to that of oocytes matured in a 1-μL droplet. Also, the culture density in a 5-μL droplet during IVM resulted in a higher (P < 0.05) rate of cleaved embryos than that in a 1-μL droplet and produced a similar rate of blastocysts compared with that of a group culture system. Conversely, BCB selection did not improve cleavage and blastocyst formation. In conclusion, it was possible to predict porcine oocytes competent for maturation using oocyte selection with BCB. Moreover, a 5-μL droplet during the individual IVM culture was most suitable for oocyte maturation and subsequent embryo development, although every culture density used in this study supported development up to the blastocyst stage.