Effect of glucose levels during the in vitro culture in synthetic oviduct fluid medium on in vitro development of bovine oocytes matured and fertilized in vitro

The present study was conducted to determine the optimal glucose levels during the in vitro culture of bovine oocytes matured and fertilized in vitro for blastocyst development. Oocytes matured in TCM-199 + 10% FCS + hormones and granulosa cells were fertilized in vitro in a TALP medium with frozen-thawed, swim-up separated, and heparin-treated spermatozoa. After insemination, 1199 oocytes were cultured for 3 days in synthetic oviduct fluid medium (SOFM) supplemented with 10% human serum (HS) and with 10 different glucose levels (0 to 5 mM), and further cultured for 5 days in SOFM + 10% HS containing 1.5 mM glucose (Experiment 1). In Experiment 2, 739 oocytes were cultured for 3 days following insemination in either SOFM + human serum albumin or SOFM + 10% HS containing 0.188 mM glucose. From Days 4 to 8, the oocytes were cultured in SOFM containing 4 different glucose levels. A high level of glucose (3.0 and 5.0 mM) at Days 0 to 3 significantly reduced the rate of blastocyst development (3.0 to 4.2%), and a yet higher (5.0 mM) glucose level at Days 4 to 8 also significantly lowered the rate of blastocyst development as compared with 1.5 mM glucose (19.5% vs 29.3%). The present results indicate that a lower level (0.188 mM: 28.8% in blastocyst development) of glucose is preferable in SOFM for the in vitro development to blastocysts at Days 0 to 3 after insemination. At Days 4 to 8, the original level (1.5 mM) of glucose contained in SOFM appears to be the most effective treatment.