A condition of horses similar to chronic obstructive pulmonary disease (e.g., farmer's lung) or airway hypersensitivity (hyperreactivity) syndrome associated with asthma-type conditions in humans; horse serves as a research model. Characterized by inflammation and reduced airway elasticity around the bronchioles and alveoli; and accumulation of inspissated exudates in the small airways, with bronchiectasis, bronchospasms, smooth muscle hypertrophy and fibrosis. It reduces pulmonary function. Clinical signs include coughing, bronchitis, bronchiolitis, reduces exercise tolerance, and expiratory dyspnea that, in chronic cases, leads to a heave line on the musculature located superficially on the caudovental aspect of the abdomen. SYN: broken wind.