35 Effects of melatonin on inflammatory marker serum amyloid A in horses after exercise

Abstract

Performance horses are regularly exposed to various stressors, such as training and exercise, that negatively impact their performance which may lead to increased oxidative stress (OS) and inflammation. Although important for the adaptive response, prolonged and unresolved OS and inflammation may decrease athletic performance or cause unnecessary cellular damage. Dietary supplements, such as antioxidants, have been shown to mitigate the negative effects of OS and inflammation and therefore may enhance performance. One such antioxidant that has been of interest is melatonin. The objectives of this study were to evaluate the potential of melatonin to reduce Serum Amyloid A (SAA), a sensitive inflammatory marker, in horses after exercise. Horses (n = 6) were randomly assigned to 2 groups (CON; n = 3, no supplement or MEL; n = 3, 20 g melatonin). Horses received diet based on BW (1% BW Nutrena Impact 12% Pellets and 2% BW bermudagrass hay/d). A switchback design was used, with 2 experimental trial periods lasting 14-d with a 30-d washout period in-between. Supplementation was given orally on exercise days during each trial period. Horses underwent 1.5hr of moderate-intensity exercise (avg >90 BPM), at 0700 3 d/wk. Blood was drawn before exercise (PRE), and at 30- and 90-min post-exercise. On exercise days (ED), horses received supplementation after PRE blood draw and before exercise (0630).After the washout period, the treatment groups were swapped, and the study was repeated, resulting in 12 ED total. Blood was collected via jugular venipuncture, immediately processed to separate plasma, and stored for analysis. SAA ELISA kits (Thermo Fisher Scientific Inc., Massachusetts) were used to determine blood SAA concentration. The first and last ED of each trial period were analyzed (ED1/ED6/ED7/ED12), and interactions of treatment, time, and day were analyzed with significance set at (P ≤ 0.05). PRE ED1 and 7 were set as baseline values, with no significant differences in baseline levels between treatments (P > 0.1862). There was a significant difference between treatments at 30- (P ≤ 0.01) and 90-min (P ≤ 0.01) post-exercise on ED1, 7, and 12, with average plasma SAA concentrations being lower for MEL group at all time points. There was also a treatment*day interaction for ED1 (P = 0.0005), ED7 (P = 0.0218), and ED12 (P = 0.0001), with MEL having lower SAA blood concentrations as compared with CON. Lower concentrations of SAA in MEL horses suggest melatonin supplementation may reduce inflammatory blood markers and, in turn, may suggest lower levels of inflammation in horses after exercise.