Maternal melatonin supplementation during late-gestation nutrient restriction alters placental fatty acid transporter expression and fetal fatty acid profiles in beef heifers.

Gestational nutrient restriction can reduce fetal growth efficiency, while melatonin supplementation can mitigate some of these negative outcomes. This study investigated placental fatty acid (FA) transporter gene expression and maternal-fetal FA concentrations in cattle supplemented with dietary melatonin during late gestational nutrient restrictions. Brangus heifers (n = 29) were fed a diet of 100% of National Research Council (NRC) requirements (ADQ) or 60% of NRC requirements (RES) from d 160 to d 240 of gestation. These groups were then randomly assigned to receive 20 mg of melatonin daily or no supplement, resulting in four treatment groups (ADQ-CON, n = 7; ADQ-MEL, n = 7; RES-CON, n = 7; RES-MEL, n = 8). On d 240, heifers underwent cesarean sections, in which amniotic fluid and blood samples from both the dam and fetus were collected to determine FA profiles. Placentomes were collected to determine transporter transcript abundance. Maternal concentrations of monounsaturated FA (P = 0.001) and total omega-3 (P = 0.041) were increased in RES versus ADQ-fed dams. Melatonin supplementation did not alter maternal FA profiles (P ≥ 0.081). Fetal concentrations of total omega-6 (n-6) were increased (P < 0.05) in RES-CON versus ADQ-CON, whereas ADQ-MEL and RES-MEL did not differ. Fetal concentrations of total branch chain fatty acids (BCFA) were increased (P < 0.05) in ADQ-MEL versus RES-MEL. Interestingly, maternal concentrations of C16:0, were increased (P = 0.015) in RES vs ADQ-fed dams, while the opposite was observed for amniotic fluid concentrations of C16:0 which were decreased (P = 0.003) in RES vs ADQ-fed dams. Amniotic fluid concentrations of total BCFA were decreased (P = 0.019) in RES versus ADQ-fed dams. Both caruncular and cotyledonary transcript abundance of CASR were decreased (P < 0.05) in RES-CON versus ADQ-CON, while melatonin supplementation rescued this depression in the cotyledon. Both caruncular and cotyledonary transcript abundance of SLC27A1 were increased (P < 0.05) in RES versus ADQ-fed dams. These results indicate that maternal melatonin supplementation differentially altered placental FA transporter transcript abundance and fetal FA profiles, demonstrating context-dependent effects under adequate versus restricted maternal nutrition.