Melatonin and tannic acid supplementation in vitro improve fertilization and embryonic development in pigs

The objective of this study was to determine the effects of melatonin supplementation during maturation and tannic acid supplementation during IVF on fertilization kinetics and early embryonic development. Experiment 1 determined the optimum concentration of melatonin supplemented to the oocytes for subsequent embryonic development. Oocytes (n = 400) were supplemented at 22 h of maturation with 0, 75, 100, or 150 nm melatonin and then subjected to IVF and embryo culture. After IVF, a portion of the embryos were evaluated for penetration, polyspermy, and male pronuclear (MPN) formation rates. Embryos were evaluated 48 h after IVF for cleavage and 144 h for blastocyst formation. There were no significant differences between treatment groups with respect to penetration and polyspermy. Supplementation of 150 nm melatonin produced a significantly greater (P < 0.05) percent of embryos with MPN compared to those supplemented with 75 nm or 100 nm. Supplementation of 150 nm melatonin produced significantly less (P < 0.05) embryos cleaved by 48 h after IVF while 75 nm melatonin supplementation had a significantly higher (P < 0.05) percentage of blastocyst formation by 144 h after IVF. Based on the optimal concentration of melatonin observed in experiment 1, experiment 2 determined the effects of supplementing 75 nm melatonin to the maturation media and 5.0 μg/ml tannic acid supplementation during IVF on oxidative stress, fertilization kinetics, and embryonic development. Oocytes (n = 720) were supplemented at 22 h of maturation with or without 75 nm melatonin and then fertilized with frozen-thawed sperm supplemented with or without 5 μg/ml tannic acid. Reactive oxygen species levels were measured in matured oocytes using 2',7'-dichlorodihydrofluorescein diacetate. Oocytes supplemented with 75 nm melatonin had significantly less (P < 0.05) reactive oxygen species generation and oocytes fertilized with sperm incubated with tannic acid had a significantly less (P < 0.05) incidence of polyspermic penetration compared to no supplementation. All treatment groups had significantly greater (P < 0.05) incidence of male pronuclear formation compared to oocytes not supplemented with melatonin and fertilized without tannic acid. Oocytes that were supplemented with melatonin and fertilized with sperm incubated with tannic acid had a significantly higher (P < 0.05) percentage of blastocyst formation by 144 h post-IVF compared all other treatment groups. Results indicate that supplementation of 75 nm melatonin during oocyte maturation and 5 μg/ml tannic acid during IVF leads to a decrease in oxidative stress, increase in IVF success and subsequent embryo development in pigs.