758 AJVR, Vol 70, No. 6, June 2009 I t has been established that exercise causes oxidative stress in humans 1,2 and rats. 3 Therefore, reducing oxi- dative stress (ie, free radical production) and inflamma- tion during exercise may improve recovery. This has led to several investigations evaluating the effect of antiox- idant supplementation in humans during exercise. 4–18 Several studies 4–11 have revealed reductions in markers of oxidative stress with antioxidant supplementation, compared with placebo treatments. However, some studies 15–18 have detected no effect of antioxidant sup- plementation on markers of running-induced oxidative stress. Most studies 5,6,16,17,19,20 have detected no effect of antioxidant supplementation on markers of muscle damage after running, although some have. 18,21 Several studies 6,7,17,19,22 have detected no effect of antioxidant supplementation on markers of inflammation after pro- Effect of a tart cherry juice blend on exercise- induced muscle damage in horses 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 Objective—To evaluate whether administering a tart cherry juice blend (TCJB) prior to ex- ercise 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 exer- cise 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, administra- tion 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. (Am J Vet Res 2009;70:758–763) longed running. Ingestion of a TCJB reduced markers of exercise-induced muscle damage in humans. 23 The actions of cyclooxygenase-inhibiting flavonoids 24,25 and anthocyanins associated with high antioxidant and anti-inflammatory activities of tart cherries 24,26,27 were thought to be responsible for this effect, although this was not investigated. Horses in various athletic competitions, such as endurance horses 28–30 and racehorses, 31,32 are exposed to oxidative stress and muscle damage. Shortening the recovery time after an exercise event would yield a substantial advantage to owners, trainers, and horses. Certain markers have been used in horses to estimate oxidative stress and inflammation. The TBARS test measures lipid peroxidation that results from oxidative stress, which results in formation of free radicals that react intracellularly to form other substances, such as malondialdehyde. 29,32,33 Such substances can cause cel- lular damage that varies from mild to severe. Many al- Received May 23, 2008. Accepted August 27, 2008. From the Departments of Clinical Sciences (Ducharme, Fortier, Kraus, Hackett, Soderholm, Mitchell) and Population Medicine and Diagnostic Sciences (Mohammed), College of Veterinary Medicine, Cornell University, Ithaca, NY 14853; the Epizootic Research Cen- ter, Equine Research Institute, Japan Racing Association 1400-4 Shiba, Shimotsuke-shi, Tochigi 349-0412, Japan (Hobo); and the Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, 130 E 77th St, New York, NY 10021 (McHugh). Supported by a grant from CherryPharm Incorporated. Address correspondence to Dr. Ducharme. ABBREVIATIONS AST Aspartate aminotransferase CK Creatine kinase cTnI Cardiac troponin I SAA Serum amyloid A TBARS Thiobarbituric acid reactive substances TCJB Tart cherry juice blend