RESUMO
Melatonin is a universal antioxidant that improves in vitro embryo production in several species. The aims of this study were to determine the melatonin concentration in the ovarian follicular fluid (FF) of juvenile goats and the effect of melatonin during in vitro maturation (IVM) on embryo development. The FF melatonin concentration was 0.57--1.07×10-9 M, increasing with follicular diameter. Oocytes were matured, fertilised and cultured under conventional conditions. Blastocyst development, embryo quality and levels of reactive oxygen species (ROS) and reduced glutathione were assessed. In Experiment 1 different melatonin concentrations (10-3, 10-7, 10-9, 10-11 M) were added to the IVM medium, which contained cysteamine as antioxidant, and no differences were observed. In Experiment 2, melatonin (10-7 M) was tested in the presence or absence of cysteamine (experimental groups: melatonin, cysteamine, melatonin+cysteamine, non-antioxidant). The melatonin group presented a higher blastocyst rate than the non-antioxidant group (28.9 vs 11.7%; P<0.01) and a higher total cell number than the cysteamine group (225.1 vs 129.0; P<0.05). Oocytes from the melatonin and cysteamine groups had lower ROS levels than those from the non-antioxidant group. This study shows that melatonin is an interesting tool for improving oocyte competence in juvenile goats as it increases embryo production and quality.