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Effects of dietary melatonin supplementation on total serum nitrites and antioxidant capacity of late gestating Holstein heifers
Previous studies have shown that dietary melatonin supplementation increased total placental nitrites and placental antioxidant capacity in ewes, while limited data exists in cattle. Therefore, our objective was to determine the effects of dietary melatonin supplementation on total serum nitrites and total serum antioxidant capacity in late gestating Holstein heifers. Dairy heifers were artificially inseminated with sex-sorted semen in January of 2013. Prior to d 170 of pregnancy, heifers (n = 20) were trained to acquire feed from the Calan feeding system. On d 190 of gestation, heifers were blocked by BW and randomly assigned to one of two dietary treatments consisting of 20 mg of dietary melatonin per day (MEL) or no melatonin supplementation (CON). At 0800 h, MEL heifers received 0.7 kg of grain top dressed with 2 mL of 10 mg/mL melatonin in ethanol while CON heifers received 0.7 kg of grain top dressed with 2 mL of ethanol alone. After consuming the grain all heifers were provided a TMR. Blood samples were collected from the tail via venipuncture of the coccygeal vein on d 180 (baseline), 210, 240, and 262 of gestation. Serum samples were analyzed for total nitrites and total antioxidant capacity using commercially available colorimetric kits. Data were evaluated using repeated-measures ANOVA of the MIXED procedure of SAS with the model statement containing dietary treatment, gestational day, and their respective interaction. Main effects of dietary treatment or gestational day are discussed in the absence of significant (P < 0.05) treatment by day interactions. Total serum nitrites were increased (P < 0.001) with increasing gestational age while no difference (P = 0.73) was observed between dietary treatments. A main effect of gestational day (P < 0.05) was observed for total serum antioxidant capacity, which was increased on d 210, 240, and 262 compared to d 180 of gestation. In addition, a main effect of dietary treatment (P < 0.001) was observed for total serum antioxidant capacity, which was increased by 40% in MEL vs. CON. Dietary melatonin supplementation during late gestation increased total antioxidant capacity in the blood while no effect was observed on total serum nitrites. In conclusion, dietary melatonin supplementation may be used to decrease oxidative stress during late pregnancy, which may improve fetal development and placental functional capacity.
Keywords: antioxidant, melatonin, pregnancy