Effects of single and double exposure to brilliant cresyl blue on the selection of porcine oocytes for in vitro production of embryos

The aim of this study was to evaluate the effectiveness and toxicity of single and double application of the brilliant cresyl blue (BCB) test on the selection of porcine oocytes as an indirect measure of oocyte growth for in vitro fertilization (IVF) and nuclear transfer. In the first experiment, oocytes were exposed to BCB before and after maturation culture and classified according to their cytoplasmic coloration: blue coloration and colorless. The classified oocytes were fertilized with spermatozoa and then cultured for 7 days. The percentages of maturation to metaphase II in blue oocytes at the start of maturation culture were higher than those of colorless oocytes (68.7-70.1% versus 0.8-3.6%, P < 0.05). However, double application of BCB test before and after maturation culture had a toxic effect on fertilization and embryonic development. No significant differences in the blastocyst formation were found between blue oocytes without double application of BCB test and control oocytes without any application of BCB test, whereas the total cell number per blastocyst from the blue oocytes was higher than that from the control oocytes (48.0 versus 34.2, P < 0.05). In the second experiment, oocytes were exposed to the BCB test before or after maturation culture, and then the matured oocytes were activated to evaluate the ability of parthenogenetic development. The proportion of blastocyst formation of blue oocytes classified after maturation culture was lower than that of blue oocytes classified before maturation culture (10.0% versus 27.0%, P < 0.05). Therefore, double application of the BCB test before and after maturation culture impaired fertilization and embryonic development, whereas a single application before maturation culture was efficient to select oocytes for IVF and nuclear transfer.