Intravenous maternal L-arginine administration to twin-bearing ewes during late pregnancy enhances placental growth and development

This study aimed to investigate if intravenous maternal Arg administration to well-fed twin-bearing ewes, from 100 to 140 d of gestation or birth, could enhance placental development and placental nutrient transport. Ewes received intravenous infusions of saline (control) or 345 MU mol Arg HCl/kg of BW 3 times daily from d 100 of pregnancy (P100) to d 140 of pregnancy (P140; cohort 1) or from P100 to birth (cohort 2). At P140, ewes in cohort 1 were euthanized and individual placentae per fetus were dissected and placentomes were classed per type (A to D) and size (light to heavy). Placentome number and individual weight were recorded. As an indicator of placental nutrient transport, blood plasma was collected from the uterine ovarian vein (UOV), uterine artery (UA), and umbilical vein and artery at the time of euthanasia and analyzed for metabolites and free AA concentrations. The ewes in cohort 2 were allowed to lamb and lambs were weighed at birth. The expelled placenta was dissected and number of cotyledons and weights of total cotyledons, remaining fetal membranes, and total placenta were recorded. At P140, Arg-infused ewes had a 63% (P = 0.03) greater number of unoccupied caruncles than control ewes. No differences were observed for placental weight at P140. At birth, lambs from Arg-infused ewes tended to have 11% (P = 0.09) greater placental weight and 34% (P = 0.03) greater total cotyledon weight compared with control lambs. Arginine-infused ewes (Arg-infused) had increased concentrations of Arg (P = 0.0001) and ornithine (Orn; P = 0.004) but decreased concentrations of Met (P = 0.01) and His (P = 0.02 and P = 0.09, respectively) compared with control ewes in plasma UOV and UA. Fetuses from Arg-infused ewes had increased concentrations of Orn (P = 0.005) and decreased concentrations of His (P = 0.006), Met (P = 0.003), and Lys (P = 0.01) but no differences in Arg (P > 0.10) concentrations were found compared with control fetuses in umbilical artery and vein plasma. This study showed that maternal Arg administration of well-fed twin-bearing ewes during late pregnancy tended to improve placental growth and development.