80 DEVELOPMENT OF A SYNTHETIC MEDIUM FOR THE IN VITRO CULTURE OF BOVINE EMBRYOS

Abstract

In the majority of media for embryo culture, 2 of typical components used are FCS or BSA; however, the presence of FCS in the culture medium has been shown to have a negative effect on embryo quality and the use of animal-derived proteins in culture media increases the risks of disease transmission through in vitro embryo production. The aim of this study was to develop an in vitro embryo culture medium free from FCS and BSA, but with the addition of various growth factors and cytokines (GF-CYK: IGF-I, IGF-II, bFGF, LIF, GM-CSF) 50 ng mL^–1 and (TGF-β1) 100 ng mL^–1 supplemented with hyaluronan (HA) and recombinant albumin (RA). Bovine oocytes (n = 1043, 6 replicates) from abattoir ovaries were matured in TCM-199 medium with 60 μg mL^–1 penicillin, 60 μg mL^–1 streptomycin, and 10 ng mL^–1 EGF for 24 h at 39°C and 5% CO₂ in humidified air. Afterward, the oocytes were fertilized in IVF-TALP medium with 6 mg mL^–1 fatty acid-free BSA and 1.7 IU mL^–1 heparin for 18 h under the same conditions. After fertilization, presumptive zygotes were divided into two groups and cultured in 30 μL droplets of SOF supplemented with (1) 0.4% BSA + 5 μg mL^–1 insulin, 5 μg mL^–1 transferrin, and 5 ng mL^–1 selenium (ITS) as a control; or (2) GF-CYK + 0.5 mg mL^–1 HA + 0.15% RA (M1). Droplets were preserved under mineral oil in a humidified atmosphere of 5% CO₂, 5% O₂, and 90% N₂ at 39°C. Blastocyst development and blastocyst diameter was observed at 7 and 8 days post-fertilization (dpf). Developmental and diameter data were analysed using the Wilcoxon test by using R software. The blastocyst rates were not significantly different between the control and M1 medium: at 7 dpf (22.9% ± 4.8 and 30.2% ± 3.0), and at 8 dpf (29.6% ± 5.1 and 37.4% ± 2.0 respectively; P > 0.05). The blastocyst diameter obtained with the M1 medium was significantly greater (P < 0.05) than that of the control at 7 dpf (173.3 μm ± 4.9 and 157.2 μm ± 4.1, respectively); however, no significant differences were observed at 8 dpf (190.3 μm ± 5.2 and 179.7 μm ± 5.3, respectively). In conclusion, the FCS- and BSA-free medium with GF-CYK, HA, and RA (M1) showed a comparable development rate to the control medium at 7 and 8 dpf. These growth factors and cytokines in association with hyaluronan and recombinant albumin have a synergistic action by promoting an increase in the blastocyst diameter at 7 dpf. This is fully synthetic method of embryo culture; it presents a valuable tool to reduce the risks of disease transmission via embryo transfer.