PSIII-26 - The Effects of Maternal Melatonin Supplementation During Pregnancy on Longissimus Dorsi Muscle Morphometrics in Bovine Fetuses at 240 Days of Gestation

Melatonin is a multifunctional hormone that positively impacts postnatal growth and weaning weight in cattle offspring when supplemented to adequately fed dams during gestation. However, it is unclear whether supplemental melatonin is effective as a countermeasure to decrease effects of a nutritionally compromised pregnancy on fetal tissues. The current study evaluated the efficacy of maternal melatonin supplementation during gestation, as a therapeutic in nutrient restricted beef heifers using fetal LM morphometrics for evaluation of carcass tissue growth. On gestational d 160, 25 Brangus heifers were assigned to one of four groups in a 2 x 2 factorial: nutrient restricted (RES-CON: 60% NRC; n = 6), adequate fed (ADQ-CON; 100% NRC; n = 6), nutrient restricted supplemented with 20 mg melatonin (RES-MEL; n = 7), or adequate fed supplemented with 20 mg melatonin (ADQ-MEL; n = 6). Treatments were top-dressed with 2 mL of melatonin dissolved in 100% ethanol (10 mg/mL) or 2 mL of ethanol (control). At gestational d 240, Caesarean sections and fetal necropsies were performed, both fetal LM were dissected to determine weight, length, and midline circumference. Data were analyzed using the MIXED procedure of SAS. There was a diet by treatment interaction wherein the mass of the left and right LM was increased (P0.035) by an average of 42.46 g in RES-MEL offspring compared to RES-CON fetuses, but no differences (P0.0812) among ADQ groups. Restricted nutrition decreased left LM circumference (10.21 vs. 10.95 cm; P = 0.0445). Treatment had no effect on LM length (P0.1139). In the present study, maternal melatonin supplementation during the Summer promoted muscle growth and mitigated the adverse effects of a nutritionally compromised pregnancy on LM morphometrics. These data are indicative of the potential for melatonin as a gestational therapeutic for prenatal muscle growth and improved efficiency of meat animal production.