Developmental competence of bovine oocytes selected based on follicle size and using the brilliant cresyl blue [BCB] test

ABSTRACT

Many studies reported that follicle size has an essential role in developmental potential of oocytes. Also, the brilliant cresyl blue [BCB] test is one of the most important criteria in selection of more competent oocytes. Selection of developmentally competent bovine oocytes. A total of 1730 bovine cumulus oocyte complexes [COCs] were recovered from the ovaries by follicles isolation and classified into 3 categories according to the diameters of the follicles [small, <3 mm; medium 3-6 mm and large >6 mm]. Oocytes were exposed to the BCB stain, diluted in Dulbecco's phosphate-buffered saline, modified with 0.4% bovine serum albumin [BSA] for 90 min. Oocytes with or without blue coloration of the cytoplasm were designated as BCB[+] and BCB[-], respectively. The BCB[+] and control oocytes originated from large and medium follicles exhibited a higher [p<0.0001] cleavage and blastocyst rate than BCB[2] oocytes. Furthermore, the BCB[+] oocytes from large and medium follicles had the highest [p<0.0001] proportion of blastocyst than other treatment groups. In contrast, the BCB[-] oocytes from small follicles had the lowest [p<0.0001] proportion of blastocyst than other treatment groups. Interestingly, the percentage of the BCB[+] oocytes from the large and medium ovarian follicles was significantly higher [p<0.0001], than the BCB[+] oocytes from the small follicles. Current results confirmed that each BCB[+] oocyte could not lead to perfect embryo development and the BCB test is not sufficient enough for the identification of oocytes that are competent for in vitro embryo development