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

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

Effect of various concentrations of minimal essential medium vitamins [MEM vitamins] on development of sheep oocytes during in-vitro maturation

Improvements in culture media formulations have led to an increase in the ability of sheep embryo in culture throughout the preimplantation period. This study was carried out to evaluate the effects of various concentrations of MEM vitamins during in vitro maturation of sheep oocytes and subsequent embryo development. Sheep ovaries were collected from a slaughterhouse and transported to the laboratory. Oocytes were matured in SOF medium supplemented with, eCG, hCG and EGF in various concentrations of MEM vitamins [control, 0.5, 1 and 1.5x] for 24h. The cumulus oocyte compelex [COCs] were co-incubated with epididymal spermatozoa of post mortem rams in synthetic oviduct fluid fertilization [SOFF] medium with 10% heat inactivated estrous sheep serum for 18h. Embryos were cultured in synthetic oviduct fluid culture 1 [SOFC1] medium for 48h followed by cultured in synthetic oviduct fluid culture 2 [SOFC2] medium for six days. Addition of 0.5 and 1 x MEM vitamins significantly increased [P< 0.05] overall blastocyst development [21.62% and 22.33%; respectively] compared with 1.5x MEM vitamins [15.59%], but there was no difference between control, 0.5 and 1x MEM vitamins in the percentage of embryos successfully developing to the blastocyst stage [19.50%, 21.62% and 22.33% respectively]. It seems that addition of 1.5x of MEM vitamins has detrimental effect on blastocyst rate