18. Effects of Melatonin Supplementation and Maternal Nutrient Restriction on Fatty Acid Transport During Late Gestation in Beef Cattle

Abstract Nutrient restriction during gestation can impair fetal growth efficiency, jeopardizing offspring survival and later productivity. Studies have shown melatonin supplementation during maternal nutrient restriction (MNR) enhances placental nutrient transporter abundance, helping to mitigate fetal nutrient deficiencies. This study aimed to examine fatty acids profiles and placental fatty acid transporter abundance in nutrient restricted dams supplemented with melatonin. To realize this objective, Brangus heifers (n = 29) were fed either 100% of NRC requirements (ADQ) or 60% of NRC requirements (RES) from d 160 to d 240 of gestation. These groups were randomly assigned to receive either 20mg of melatonin supplement daily or no supplement, constructing four treatment groups (ADQ-CON, n = 7; ADQ-MEL, n = 7; RES-CON, n = 7; and RES-MEL, n = 8). On d 240, maternal blood, fetal blood and amniotic fluid were collected for fatty acid analysis. Placentomes were collected to determine gene transcript abundance via RT-PCR techniques. MNR increased (P ≤ 0.05) SLC27A1 transcript abundance, a common long chain fatty acid transporter, in both the caruncle and cotyledon compared with ADQ fed dams. Caruncle SLC27A4 transcription abundance was increased (P ≤ 0.005) in RES-MEL compared with all other treatment groups. Maternal concentrations of total monounsaturated (P ≤ 0.001) and total omega-3 (P ≤ 0.041) fatty acids were increased in RES dams compared with ADQ dams. Melatonin treatment did not influence maternal fatty acid profiles (P ≥ 0.081). Fetal concentrations of margaric acid, C17:0, were decreased (P = 0.022) in RES-MEL compared with RES-CON. Fetal concentrations of total omega-6 fatty acids were increased (P = 0.026) in the RES-MEL group when compared with ADQ-CON. Concentrations of oleic acid, C18:1c9, and C18:1 c12 were increased (P ≤ 0.047) in RES-CON fetuses compared with ADQ-CON, while RES-MEL and ADQ-CON had similar (P ≥ 0.188) circulating concentrations. Fetal branch chain fatty acids concentrations were decreased (P ≤ 0.003) in RES-MEL, driven by a decrease in 15-methylpalmitic acid, when compared to RES-CON group (P ≤ 0.003). Amniotic fluid exhibited increased concentrations of oleic acid in RES-MEL when compared with all other treatment groups (P = 0.047). Nutrient restriction decreased (P ≤ 0.019) total branch chain fatty acids circulating in amniotic fluid when compared with ADQ-CON group. With supplementation, RES-MEL recovered total branch chain fatty acid and 15-methylpalmitic acid concentrations in amniotic fluid (P ≥ 0.107). This study demonstrated melatonin supplementation alters placental fatty acid transporter abundance, resulting in partial rescue of fatty acid profiles in fetal and amniotic fluid in nutrient restricted dams.