Effects of follicular fluid during in vitro maturation of bovine oocytes on in vitro fertilization and early embryonic development.

Abstract

In vivo, oocytes mature while bathed in preovulatory follicular fluid, so we studied maturation of oocytes in vitro in media supplemented with such fluid. Bovine oocytes were obtained from 2-to 6-mm follicles from slaughterhouse ovaries and were matured for 24 h in tissue culture medium 199 + 10% estrous cow serum supplemented with bovine follicular fluid (BFF) obtained from a preovulatory follicle either before (0 h) or 8 or 20 h after a GnRH-induced LH surge. After in vitro fertilization, oocytes matured in 10% or 40% 20-h BFF had higher cleavage rates (p < 0.05) than those matured in 10% or 40% 0-h BFF (80% and 86% vs. 46% and 51%, respectively); oocytes matured in 8-h BFF were intermediate. A greater percentage of oocytes showed cumulus expansion with 20-h BFF than with 0-h BFF (p < 0.05). In experiment 2, more (p < 0.05) embryos from oocytes matured in 20% or 40% 20-h BFF developed to blastocysts after culture of embryos compared to those matured in 20% or 40% 0-h BFF (29% and 29% vs. 7% and 14%, respectively) or those matured in no BFF (12%). Embryos from oocytes matured in a mixture of 0-h and 20-h BFF developed to the blastocyst stage similarly (27%) to those matured in 20-h BFF, suggesting that positive factors in 20-h BFF overcame any inhibitory effect of 0-h BFF. To summarize, bovine oocytes matured with BFF collected 20 h after LH surge result in higher cleavage rates after in vitro fertilization and more blastocysts than those matured in 0-h BFF. When the factors responsible are identified, they might be used to enhance maturation of oocytes in vitro.