Lipid content, active mitochondria and brilliant cresyl blue staining in bovine oocytes

Bovine oocytes that stain with brilliant cresyl blue (BCB) have a relatively higher developmental competence. The aim of the present study was to investigate the relationships among BCB staining, lipid content, and active mitochondria. Bovine oocytes (N = 133) with at least three layers of cumulus cells were segregated as BCB retained (BCB+) or metabolized (BCB-) and then stained for active mitochondria (Mitotracker Red) and lipid (Bodipy), with analysis by confocal microscopy. The BCB+ oocytes (N = 45) contained approximately 26% more cytoplasmic lipid than BCB- oocytes (N = 26-27; P < 0.05). Staining for active mitochondria did not differ between the groups. In BCB- oocytes but not BCB+ oocytes, lipid content correlated with active mitochondrial staining (r = 0.48; P < 0.05). Diameter correlated with lipid content for BCB+ oocytes (r = 0.46; P < 0.05), but not for BCB- oocytes (r = 0.16; P > 0.05). Irrespective of BCB staining, both lipid and active mitochondrial content correlated with diameter. In conclusion, the higher lipid content of BCB+ bovine oocytes might provide a cellular and functional basis for their greater developmental competence.