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Supplement: Waltham International Symposium

Changes in Circulatory Antioxidant Status in Horses during Prolonged Exercise

David J. Marlin³, Katie Fenn, Nicola Smith, Chris D. Deaton, Colin A. Roberts, Patricia A. Harris^*, Christina Dunster and Frank J. Kelly

Center for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, UK; ^* Equine Studies Group, Waltham Center for Pet Nutrition, Leicestershire, UK and Lung Biology, School of Health and Life Sciences, King’s College London, London, UK

³To whom correspondence should be addressed. E-mail: david.marlin{at}aht.org.uk.

Prolonged low-medium intensity exercise is associated with increased oxidative stress in humans. We hypothesized that competitive equine endurance racing would induce changes in circulatory antioxidants and produce systemic oxidative stress. Forty horses competing in a 140-km endurance race in warm conditions [shade temperature 15–19°C; 62–88% relative humidity (%RH)] were sampled before (Pre), immediately after exercise (End) and at approximately 16 h into recovery (+16 h). Plasma ascorbic acid concentration was not different between Pre [11.1 (median); 4.6–20.3 µmol/L (range)] and End [9.7; 3.0–38.9 (range) µmol/L] but was significantly decreased at +16 h (5.5; 2.8–15.5 µmol/L; P < 0.05). Total red cell hemolysate glutathione (TGSH) concentration was significantly reduced by exercise (Pre 1261; 883–1532 µmol/L; End 1065; 757–1334 µmol/L; P < 0.05) and at +16 h recovery (1032; 752–1362 µmol/L; P < 0.05). Glutathione redox ratio was unchanged by exercise but was significantly decreased at +16 h compared with that at both Pre and End (P < 0.05). The concentration of total barbituric acid reactive substances (TBARS) in plasma was increased compared with that at Pre (309; 66–1048 nmol/L), both at End (408; 170–1196 nmol/L; P < 0.05) and +16 h (380; 99–1161 nmol/L; P < 0.05). -Tocopherol was unchanged by exercise or recovery. Mean race speed was 16.5 ± 1.6 km/h and ranged from 13.9 to 19.7 km/h. Mean speed during competition in horses that completed the full 140 km (n = 28) was significantly correlated with end of exercise ascorbic acid (r = 0.622; P = 0.0004). Although there were increases in creatine phosphokinase (CK), aspartate aminotransferase (AST) and TBARS and a loss of TGSH, this study failed to demonstrate evidence of classical oxidative stress.

KEY WORDS: • horse • reactive oxygen species • antioxidants • prolonged exercise

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