Effect of Dietary L-Arginine on Blood Flow Dynamics, Gestation Length, and Placental Efficiency of Mares

Objectives were to determine effects of arginine supplementation during different times of gestation to mares on uterine blood flow, placental efficiency and uterine involution. Pregnant mares (n=20) were randomly assigned to one of four diets beginning 21 d prior to expected foaling date 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 both early and late gestation. Arginine was supplemented at 1 % of diet. Ultrasonography was conducted to measure uterine blood flow at 21 d prior to expected foaling date (late gestation), then every two weeks until foaling, d 1, 4, and 7 after foaling to measure uterine involution, then every 14 d after breeding until 84 d of gestation (early gestation). Placentas were weighed, surface area and displacement volume were determined. Placental efficiency was calculated using foal wt and placental wt. Mixed procedures with repeated measures in SAS were used for blood flow parameters, and uterine involution parameters, while placental efficiency and gestation length data were subjected to Mixed procedures. Treatment did not affect ipsilateral or contralateral uterine artery measurements during late gestation of resistance index (RI; P>0.05), pulsatility index (PI; P>0.05), and blood flow (P>0.05) or during early gestation of PI (P>0.05), blood flow (P>0.05), and heart rate (HR; P>0.05). Ipsilateral uterine artery measurements during late gestation of RI (P=0.03) increased as trial progressed. Ipsilateral uterine artery measurements for early gestation of RI (P=0.03) were different over time. There was a treatment by time interaction for RI in contralateral uterine artery in early gestation (P=0.04) in which mares on E had increased RI on d 84. Total blood flow for mares in late or early gestation (P=0.52; P=0.74 respectively) was not effected by treatment. Average HR (P=0.04) increased over time and was decreased (P=0.01) for all mares consuming arginine. Total blood flow for mares during 7 d post-foaling (P=0.29) was not effected by treatment. Whole uterine diameter during 7 d post-foaling had a treatment by day interaction (P<0.01) with mares receiving arginine prior to foaling having smaller uterine diameter during 7 d post-foaling compared to mares either on C or E. Uterine fluid during 7 d post-foaling was not affected by treatment (P=0.01). Further research is continuing on arginine supplementation to gestating mares.