78
Effects of dietary melatonin supplementation during late gestation on uterine artery hemodynamics in Holstein heifers
The objective was to examine the effects of melatonin supplementation during late gestation on uterine artery hemodynamics in Holstein heifers. Prior to d 170 of pregnancy, heifers were trained to acquire feed from the Calan feeding system. On d 190 of gestation, heifers (n = 20) were blocked by BW and then randomly assigned to one of two dietary treatments: 1). 20 mg of dietary melatonin per day (MEL) or 2). 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. A TMR was provided after grain consumption. Supplementation ceased on d 262 of gestation for both treatment groups. Uterine artery hemodynamics, contralateral and ipsilateral to the conceptus, were obtained on d 180 (baseline), 210, 240, and 262 of gestation via Doppler ultrasonography and included resistance index (RI), pulsatility index (PI), and blood flow (BF). Dependent variables were analyzed 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. Contralateral RI (P = 0.43), PI (P = 0.29), and BF (P = 0.74) were not different between dietary treatments. Contralateral RI (P = 0.11) and PI (P = 0.09) were not different among gestational days; however, contralateral BF increased (P < 0.001) from d 180 to d 240 of gestation. Ipsilateral RI (P = 0.18) and PI (P = 0.25) were not different between dietary treatments; however, ipsilateral BF was increased (P = 0.01) in MEL vs. CON. Ipsilateral RI (P = 0.04) and PI (P < 0.01) decreased, while BF (P < 0.001) increased as gestation proceeded. Total uterine artery BF (summation of ipsilateral and contralateral) was increased (P < 0.01) in MEL vs. CON. Maternal heart rate was increased (P = 0.04) in MEL vs. CON, while maternal mean arterial pressure was not different (P > 0.06). In conclusion, dietary melatonin supplementation during late gestation increased uterine artery BF. Therefore, melatonin could be used to potentially increase uterine BF during a compromised pregnancy.
Keywords: melatonin, pregnancy, uterine blood flow