Effect of Dietary L-Arginine on Blood Flow Dynamics, and Placental Measurements of Mares

Objectives were to determine effects of arginine supplementation during different times of gestation to mares on uterine blood flow, placental measurements and uterine involution. Pregnant mares (n=20) were randomly assigned to one of four diets beginning 21 d prior to expected foaling date (actual 20.1 d) until 84 d of next gestation. Diet 1 (C): basal diet, Diet 2 (L): C plus arginine during late gestation, Diet 3 (E): C plus arginine during early gestation, and Diet 4 (LE): C plus arginine during early and late gestation. These treatments were applied for a 2 year duration (2016 and 2017). Arginine was supplemented at 1 % of diet. Ultrasonography was conducted to measure uterine blood flow. Placentas were collected for analysis. Blood flow was not different in ipsilateral uterine artery, contralateral uterine artery, nor total blood flow. There was a treatment by day interaction (P = 0.0083) in 2016 for uterine diameter with mares receiving any arginine treatment having smaller uterine diameter on days 4 and 7 compares to C. Uterine edema score for 2017 had a treatment by day interaction (P = 0.0009), with mares receiving E and L having the least amount of edema on d 7 compared to other treatments. No differences were found for placental measures. Percent capillaries within microvilli (P = 0.0207) with samples from the gravid horn of the placenta from mares receiving C had largest percentage of capillaries within microvilli. Blood nitrite concentration during early and late gestation in 2016 were increased (P = 0.0099; P = 0.0220) in mares receiving L compared to mares receiving C and mares receiving arginine in late gestation had an increased concentration of nitrites present within placental tissue. Supplementation of arginine to mares during different time points of gestation had positive results relevant to time of supplementation.