Parthenogenetic activation of in vitro matured bovine oocytes

Bovine germinal vesicle oocytes were collected from 2- to 4-mm follicles. Oocytes were matured in medium 199 containing 10% bovine follicular fluid, FSH, and estradiol. Matured oocytes were cocultured for 2 to 24 h with dead bovine sperm in either Tyrode's medium without albumin or with 40% follicular fluid. After removal of sperm, oocytes were cultured an additional 48 to 72 h in synthetic oviduct fluid or medium 199 containing 10% follicular fluid without hormones. Oocyte activation rates (pronucleus to 8 cells), after exposure to dead sperm for 2, 4, 6, 12, or 24 h, in protein-free Tyrode's medium before embryo culture in synthetic oviductal fluid were 11, 17, 41, and 41%. Activation rates were decreased to 3, 9, 8, 27, and 34% for these same times by the addition of estrual follicular fluid to the protein-free Tyrode's medium. Substitution of bovine serum albumin for follicular fluid in the Tyrode's medium resulted in 47% oocyte activation. Activation depended on time and composition of media, occurred with high frequency with matured bovine oocytes under common in vitro culture conditions, and decreased in the presence of bovine follicular fluid. Therefore, because cleavage is not a sufficient measure of embryo quality, parthenogenetic controls must be run.