When a horse inhales mold spores or other irritants, neutrophils (specific types of white blood cells) release reactive oxidants–generally very reactive substances that can break down mold in the airways. That’s not a bad thing, really. “But if there are too many, they can attack the lung tissue,” said Chris Deaton, BSc (Hons), PhD, post-doctoral physiologist of the Animal Health Trust.

With an increase in neutrophils, there is typically an increase of mucus in the airways and a resulting constriction. This narrowing of the airways intensifies the effort the horse must make to breathe, causing the characteristic “heave line” that you see in a horse with recurrent airway obstruction. “It’s not clear if oxidation is causing airway inflammation, but we are currently investigating to find out,” Deaton adds.

For his research, Deaton is collecting breath condensate: A horse wears a special mask that collects his exhaled breath and sends it into a cooled tube where it condenses and falls into a collection chamber. Deaton takes the resulting condensate–about 2 mL–and the sample is examined in the lab for the amount of hydrogen peroxide (which is an oxidant that neutrophils produce). The levels of ascorbic acid (Vitamin C, an antioxidant) and evidence of oxidized lipids are also determined in samples of airway lining fluid collected by tracheal and bronchoalveolar lavage.

Deaton and colleagues have already determined horses with high susceptibility to oxidative stress might benefit from antioxidant supplementation. Now he’s taking that a step further and looking at which types of antioxidant supplements are best and helping develop an antioxidant treatment that “anecdotally seems to reduce the amount of coughing and offset signs of recurrent airway obstruction,” he says