307 Effect of maternal melatonin supplementation during mid to late gestation on fatty acid composition in maternal and fetal plasma and perirenal adipose tissue collected from bovine fetuses at 240 days of gestation

Melatonin supplementation during mid to late gestation increases uterine blood flow, thereby altering the flux of nutrients delivered to the developing fetus by the dam. Changes in the amount and composition of fatty acids available to the fetus can alter the long-term growth and developmental potential of the offspring in postnatal life. The objective of this study was to determine the effect of supplementing melatonin to beef heifers during mid to late gestation on fatty acid composition of maternal, umbilical, and fetal plasma as well as fetal perirenal adipose tissue. A total of 32 pregnant heifers were treated with (MEL) or without (CON) two 24-mg melatonin implants every 30 d starting on d 180 and ending on d 240 of gestation. On d 240 of gestation (approximately 85% of gestation), 6 CON and 6 MEL heifers were randomly selected to undergo Cesarean sections to collect fetal blood and tissues. Maternal blood (MB) was collected from the tail vein of the dams immediately prior to the surgery. Before excising the fetus, the umbilical cord was clamped on the fetal and maternal ends to collect blood from the umbilical artery (UA) and umbilical vein (UV). Fetal peripheral blood (FB) was collected during exsanguination, and perirenal (PR) adipose tissue was dissected from the fetal kidney following evisceration. Plasma and PR adipose tissue samples were directly derivatized for fatty acid quantification on a gas chromatography system to determine fatty acid concentration and percentage by internal calibration. Data were analyzed using the GLIMMIX procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC), and statistical significance was determined at P ≤ 0.05. There was no difference in total plasma fatty acid concentrations between the CON and MEL groups in MB, UA, UV, FB or PR (P > 0.324). Total SFA, MUFA, and PUFA in UA, UV, MB, FB, or PR also did not differ between treatments (P ≥ 0.11). However, MEL tended to increase C22:6 fatty acid concentration in MB (P = 0.065), UV (P = 0.079), and FB (P = 0.068). Additionally, there was a tendency for increased (P = 0.080) C20:5n-3 fatty acid in PR adipose tissue in fetuses from MEL-treated dams. Both C22:6 and C20:5n-3 fatty acids improve fetal development and immune function. Therefore, additional research is warranted to determine the specific effect of MEL on these fatty acids and their long-term impacts on offspring growth and physiology.