Effect of oocyte maturation medium on in vitro development of in vitro fertilized bovine embryos

The objective of this study was to examine the effects of different culture media used for maturation of bovine oocytes on in vitro embryo development following in vitro fertilization. Oocytes were aspirated from 2–5 mm follicles of ovaries collected at a local abattoir. The oocyte‐cumulus complexes (OCCs) were cultured for 23–25 h in one of seven commercially available media supplemented with 6 mg/ml bovine serum albumin (BSA), 0.25 mM pyruvate, 10 μg/ml luteinizing hormone (LH), 0.5 μg/ml follicle‐stimulating hormone (FSH), and 1 μg/ml estradiol. After maturation for 23–25 h, all eggs were subjected to the same in vitro fertilization protocol using modified TALP medium and subsequently cultured in the same serum‐free embryo culture medium (HECM‐1/BSA) for 8 days, after which embryo development was assessed. Five media (SFRE, MEMα, TCM199, MEMα/+, RPMI:MEMα) better supported normal oocyte maturation as determined by embryo development to the two‐cell (76–82%), morula/blastocyst (25–32%), and blastocyst (12–19%) stages. Oocytes that were matured in Waymouth's medium MB 752/1 or Ham's F‐12 had a significantly reduced incidence of cleavage to the two‐cell stage (52% and 37%, respectively), which was not attributed to failure of fertilization. Of the eggs that did cleave to the two‐cell stage in these two media, 27% and 9% developed to morulae/blastocysts but only 6% and 3%, respectively, developed into blastocysts. This study demonstrates that (1) the culture medium used for bovine oocyte maturation can markedly affect subsequent embryo development at several stages, including blastocysts, and (2) bovine oocytes can be matured and fertilized and develop to blastocysts in serum‐free medium.