Effects of iron and copper in culture medium on bovine oocyte maturation, preimplantation embryo development, and apoptosis of blastocysts in vitro

The aim of this study was to investigate the effects of iron and copper on bovine oocyte maturation, preimplantation embryo development and apoptosis of blastocysts. The concentrations of iron in the culture media were 0 (control), 0.45, 0.81, 1.96 and 3.26 mg/l, and the concentrations of copper were 0 (control), 0.093, 0.27, 0.46 and 0.68 mg/l. The changes in the iron (1.96 mg/l) and copper concentrations (0.46 mg/l) in the culture media were measured after oocyte maturation for 22 h and after zygote culture for 48, 96, 144 and 192 h. The results showed that there were no significant differences in oocyte maturation and cleavage between media containing iron and the control, but the media containing iron had higher (P>0.05) rates of 8-cell embryos, morulae, and blastocysts than the control, and addition of 1.96 mg/l of iron increased the blastocyst rate (P>0.05). The effects of copper on oocyte maturation and cleavage were similar to iron, and addition of 0.46 and 0.68 mg/l of copper increased the rates of morulae and blastocysts (P>0.05). Addition of iron or copper significantly decreased the number of apoptotic blastomeres compared with the control (P>0.05). After oocyte maturation for 22 h and zygote culture for 48 h, the iron concentrations decreased by 3.6 and 9.2%, respectively, and the copper concentrations decreased by 6.5 and 10.9%, respectively. After zygote culture for 96, 144 and 192 h, the iron concentrations decreased by 21.4, 25.5 and 27.0%, respectively, the copper concentrations decreased by 23.9, 28.3 and 30.4%, respectively. In conclusion, iron and copper played an important role in the success of culture of 8-cell embryos, morulae, and blastocysts, and long-term lack of iron or copper increased the number of apoptotic blastomeres. Furthermore, transition of primary demand for trace amounts of iron or copper from the cytoplast to culture medium for utilization by zygotes may occur after in vitro zygote culture for 48 h.