Lipid-rich bovine serum albumin is beneficial for the early development of bovine embryos, but induces lipid droplet formation in the blastocyst

Lipid-rich bovine serum albumin (LR-BSA) has been reported to increase the survival rate of blastocysts after freezing and thawing. However studies on the early development of in vitro fertilised (IVF) embryos are still insufficient in cattle. This study investigated the blastocyst productivity of in vitro culture (IVC) medium (synthetic oviductal fluid medium with amino acids, mSOFaa) supplemented with 5% fetal bovine serum (FBS, Control) or LR-BSA (1, 2.5, 5 mg/ml dosages, respectively) and the qualitative characteristics of produced blastocysts. Cleavage rates on day 2 were similar between all groups. Significant differences were obtained in the blastocyst rate in the 2.5LR-BSA group compared with the control (23.5% vs 35.7%, P < 0.05). Hatching rates were significantly higher in all treatment groups than in control (P < 0.05). The cell number in blastocysts did not differ among groups, but the apoptotic index in the 5.0LR-BSA group was higher than the control (P < 0.05). The expression of embryo quality-related markers was affected. Octamer-binding transcription factor 4 (Oct4), placenta associated 8 (Plac8), and sex-determining region Y-box 2 (Sox2) genes expression in the 2.5LR-BSA group were significantly up-regulated compared to the control (P < 0.05). Cytoplasmic lipid contents and the lipid droplet formation-related gene, sterol regulatory element binding transcription factor 1 (Srebf1), were significantly increased in the 5.0LR-BSA group (P < 0.05). Therefore, the LR-BSA supplementation (2.5 mg/ml) to mSOFaa medium could contribute to the early development of bovine IVF embryos and the qualitative improvement of the resulting blastocysts.