Recurrent
airway obstruction (RAO) or heaves is a manifestation of a
hypersensitivity to dust, moulds, and spores in the environment of a susceptible horse. Although in the majority of RAO-affected horses, clinical remission can be achieved by keeping horses at pasture to reduce their
allergen exposure, this often is not practicable. For this reason, we investigated if changing the environment of a single stall in a 4 stall stable was sufficient to improve lung function and reduce
inflammation in RAO-affected horses. In addition, we determined if addition of oral
prednisone provided additional benefit. Twelve RAO-susceptible horses were stabled, fed hay, and bedded on straw until they developed
airway obstruction. At this point, bedding was changed to wood shavings and they were fed a pelleted diet for 2 weeks. Lung function was measured and bronchoalveolar lavage was performed before and 3, 7, and 14 days after environmental modification. In a crossover design, horses were treated for the 14 days with
prednisone tablets (2.2 mg/kg bwt, q. 24 h). Horses then returned to pasture for 30 days.
Airway obstruction was greatest before environmental modification. Significant improvement in lung function occurred within 3 days of the change in environment and continued to Day 7. Airway function was best after 30 days at pasture. The clinical response achieved by environmental modification was not significantly improved by addition of oral
prednisone. The total number of cells, total neutrophils, and percent neutrophils was greatest before environmental modification. In the absence of
prednisone, total and percent neutrophils did not decrease until Day 14 and total cell number until 30 days at pasture. In the presence of
prednisone, total cells and total and percent neutrophils decreased by Day 3 and again at pasture. The fact that lung function can be improved within 3 days by environmental management alone emphasises the need for
allergen reduction as the cornerstone of treatment of RAO. Although
prednisone induced a more rapid reduction in airway
inflammation, this was not associated with a more rapid improvement in airway function.