Normand G. Ducharme, DMV, MSc; Lisa A. Fortier, DVM, PhD; Marc S. Kraus, DVM; Seiji Hobo, DVM, PhD; Hussni O. Mohammed, BVSc, DPVM, PhD; Malachy P. McHugh, PhD; Richard P. Hackett, DVM, MS; Leo V. Soderholm, BS; Lisa M. Mitchell‌ American Journal of Veterinary Research June 2009 70 6 758-763 Objective—To evaluate whether administering a tart cherry juice blend (TCJB) prior to exercise would reduce skeletal and cardiac muscle damage by decreasing the inflammatory and oxidative stress response to exercise in horses. Animals—6 horses. Procedures—Horses were randomly allocated into 2 groups in a crossover study with a 2-week washout period and orally administered either TCJB or a placebo solution (1.42 L, twice daily) in a double-masked protocol for 2 weeks prior to a stepwise incremental exercise protocol. Horses were tested for serum activities of creatine kinase and aspartate aminotransferase (AST) and concentrations of cardiac troponin I (cTnI), thiobarbituric acid reactive substances (TBARS; an indicator of oxidative stress), and serum amyloid A (SAA; an indicator of inflammation). To ensure that treatment would not result in positive results of an equine drug-screening protocol, serum samples obtained from each horse prior to and after 2 weeks of administration of TCJB or the placebo solution were tested. Results—All horses had negative results of drug screening at both sample times. The exercise protocol resulted in a significant increase in TBARS concentration, SAA concentration, and serum AST activity in all horses. Administration of TCJB or placebo solution was not associated with an effect on malondialdehyde or SAA concentrations. However, administration of TCJB was associated with less serum activity of AST, compared with administration of placebo solution. Conclusions and Clinical Relevance—Administration of TCJB may diminish muscle damage induced by exercise