Effects of in vitro-growth culture duration on fertilizability of bovine growing oocytes and proliferation of cells surrounding oocytes.

The effects of in vitro-growth (IVG) culture duration (12 and 14 days) on the fertilizability and the developmental ability of IVG oocytes matured with pre-maturational culture, and on the proliferation of cells surrounding oocytes during IVG culture were examined. The fertilization and cleavage rates of 12- and 14-day IVG oocytes were similar; however, 14-day IVG oocytes showed lower blastocyst development rate than 12-day IVG oocytes. In addition, the number of cells surrounding oocytes increased until 12 days of IVG, but decreased at 14 days. The results indicated that the extension of IVG period beyond 12 days impaired the proliferation of cells surrounding oocytes, leading to the decrease of developmental ability but not fertilizability of 14-day IVG oocytes.