RAO was defined as chronic neutrophilic pulmonary
inflammation associated with the presence of hay and/or
straw in the affected horses’ environment and with clinical
manifestations varying from mild cough to severe dyspnea
at rest. The BALF of horses with RAO showed moderate to
severe neutrophilia (>20% cells), decreased lymphocyte,
and alveolar macrophage counts [25,26]. Summer pastureassociated
(SPA)-RAO is clinically indistinguishable from
RAO except that the affected horses develop signs while
maintained on pasture [9].