Melatonin effect on bovine embryo development in vitro in relation to oxygen concentration

Melatonin promotes mouse embryo development in vitro. An effect of melatonin on bovine embryo development is described here. Slaughterhouse derived oocytes were subjected to standard in vitro maturation and fertilization procedures. Presumptive zygotes were cultured for 2 days in CR1aaLA medium supplemented with melatonin (10(-4) M) or without melatonin (control). Culture was performed under two different gas atmospheres containing physiological (7%) or atmospheric (20%) oxygen concentrations (2 x 2 factorial analysis). After day 2, embryos from each treatment group developed to at least four-cell stage, were cultured without melatonin until day 10 at optimum 7% O-2 atmosphere. Blastocyst formation rates of presumptive zygotes and of four-cell embryos were calculated for each group. Significant interactions between oxygen tension and the melatonin treatment were found. Out of four-cell embryos put into in vitro culture after initial incubation in medium containing melatonin, decreased blastocyst rate was observed in melatonin group (47.7%) compared with control (67.7%; P = 0.0327) when lower oxygen concentration was applied. A beneficial effect of melatonin was observed in 20% O-2: out of 61 embryos, 42 (68.9%) developed to the blastocyst stage after treatment in melatonin versus 32 of 63 (50.8%; P = 0.0458) blastocysts that developed in control group. In conclusion, beneficial or harmful effects of melatonin on bovine embryo development in vitro were observed, depending on the oxygen tension during the treatment.