Inflammatory airway disease (IAD) is a non-infectious condition of the lower respiratory tract characterized by lower airway inflammatory process of the bronchi and bronchioles, excessive mucus accumulation, and bronchoconstriction without systemic signs of illness. It affects horses of all ages, breeds, and disciplines—including racehorses, sport horses, and working horses—and is considered one of the most prevalent performance-limiting respiratory conditions in equine athletes. IAD differs from severe equine asthma (formerly called recurrent airway obstruction or heaves) primarily in severity: horses with IAD do not show signs of respiratory distress at rest, do not have an elevated resting respiratory rate, and do not display the characteristic heave line from hypertrophied external abdominal oblique muscles.
The causes are multifactorial. Inhaled organic dusts and molds from hay and bedding are major triggers; horses kept in poorly ventilated stalls and fed dry hay have consistently higher airway inflammatory cell counts than horses kept at pasture or fed soaked or haylage. Viral respiratory viral respiratory infections as IAD triggers—equine influenza, equine herpesvirus types 1 and 4, and equine rhinitis viruses—can initiate or exacerbate IAD by damaging airway epithelium and priming a persistent inflammatory response. Air pollutants at competition venues, diesel exhaust from transport, and endotoxin from gram-negative bacterial contamination of feed are recognized environmental contributors. Some horses appear to have an allergic component, with eosinophil-predominant cytology on tracheal wash samples suggesting hypersensitivity to specific antigens rather than generalized particulate irritation.
Diagnosis requires endoscopic assessment showing excess mucus in the trachea, combined with cytological analysis of a bronchoalveolar lavage (BAL) sample showing elevated neutrophils, mast cells, or eosinophils above reference thresholds. Clinical signs are subtle: intermittent coughing, mild nasal discharge, and reduced performance or early fatigue during exercise. Treatment centers on environmental management first—maximizing ventilation, replacing dry hay with soaked hay or complete feed pellets, and switching to low-dust bedding such as paper, cardboard, or kiln-dried shavings—because pharmacological management without removing the trigger produces only temporary improvement. Corticosteroids (inhaled or systemic) and bronchodilators (clenbuterol, albuterol) reduce lower airway inflammatory process and relieve bronchoconstriction acutely; current protocols favor inhaled corticosteroids for long-term management because systemic administration suppresses adrenal function and may worsen laminitis risk in horses with concurrent metabolic conditions. Vaccination against respiratory viruses reduces the frequency of infection-triggered exacerbations.
Further Reading
- recurrent airway obstruction in horses (Wikipedia)
- For diagnosis, management, and environmental control recommendations: inflammatory airway disease in horses — Merck Veterinary Manual