• horse;
  • ascorbic acid;
  • α-tocopherol;
  • oxidative stress;
  • lipid peroxidation


Antioxidants have been implicated in the reduction and prevention of oxidative stress during exercise. We hypothesised that a dietary supplement containing a mixture of natural antioxidants together with vitamins E, C and selenium, given for 4 weeks, would increase the systemic and pulmonary antioxidant capacity leading to a reduction in markers of oxidative damage and an improvement in pulmonary function during exercise. In 6 healthy horses studied, the antioxidant supplement significantly increased plasma concentrations of ascorbic acid (from mean ± s.d. 16 ± 7 to 23 ± 4 μmol/l; P = 0.007) and α-tocopherol (from 10 ± 3 to 14 ± 3 μmol/l; P = 0.02) and increased the bronchoalveolar lavage pulmonary epithelial lining fluid (ELF) concentration of ascorbic acid compared to a placebo, but not significantly (2.0 ± 0.9 mmol/l and 1.2 ± 0.9 mmol/l, respectively; P>0.05). α-tocopherol was not detected in ELF either before or after supplementation or exercise. The mean concentration of malondialdehyde (MDA) in ELF was lower following antioxidant supplementation compared to placebo and control periods, but not significantly. An intermittent exercise test consisting of 2 min at 70, 80 and 90% of the horses' individual maximum oxygen uptake, failed to induce significant systemic or pulmonary oxidative stress (based on the glutathione redox ratio (GRR) and the ascorbic acid redox ratio (ARR)) and lipid peroxidation (based on the concentration of thiobarbituric acid reactive substances in plasma and MDA in ELF) either for placebo or antioxidant treatments. There was a strong correlation between GRR and ARR in the pulmonary epithelial lining fluid (r = 0.89; P<0.0001). In healthy horses on a diet containing adequate levels of antioxidants, additional antioxidant supplementation has no apparent beneficial or detrimental effect on pulmonary function during moderate intensity exercise. The importance of antioxidant supplementation may only become apparent if the diet is deficient in antioxidants, if exercise intensity is higher or more prolonged, or if disease or additional stresses are present.