Environment and prednisone interactions in the treatment of recurrent airway obstruction (heaves)

Recurrent airway obstruction (RAO) or heaves is a manifestation of a hypers ensitivity to dust, moulds, and spores in the environment of a susceptible horse. Although in the majority of RAG-affected horses, clinical remission can be achieved by keeping horses at pasture to reduce their allergen expos ure, this often is not practicable. For this reason, we investigated if cha nging the environment of a single stall in a 4 stall stable was sufficient to improve lung function and reduce inflammation in RAG-affected horses. In addition, we determined if addition of oral prednisone provided additional benefit. Twelve RAG-susceptible horses were stabled, fed hay, and bedded o n 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. Lu ng function was measured and bronchoalveolar lavage was performed before an d 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 bw t, q. 24 h). Horses then returned to pasture for 30 days. Airway obstructio n was greatest before environmental modification. Significant improvement i n lung function occurred within 3 days of the change in environment and con tinued to Day 7. Airway function was best after 30 days at pasture. The cli nical 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 modi fication. In the absence of prednisone, total and percent neutrophils did n ot 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 ne ed for allergen reduction as the cornerstone of treatment of RAG. Although prednisone induced a more rapid reduction in airway inflammation, this was not associated with a more rapid improvement in airway function.