Inflammatory Airway Disease (IAD)
Inflammatory airway disease (IAD) is, as its name suggests, a disease caused by inflammation of the respiratory tract in the horse. It has much in common with heaves or RAO (recurrent airway obstruction), especially with regards to its main cause: exposure to dust. Nevertheless, the symptoms are much less severe in cases of IAD than in heaves.

Inflammatory airway disease (IAD) is, as its name suggests, a disease caused by inflammation of the respiratory tract in the horse. It has much in common with heaves or RAO (recurrent airway obstruction), especially with regards to its main cause: exposure to dust. Nevertheless, the symptoms are much less severe in cases of IAD than in heaves.
A frequent problem, discrete clinical signs
IAD affects many horses of all ages. This disease is frequent in race horses (trotters and gallopers) as well as sports and leisure horses. However, it is not always easy to identify. Indeed, the clinical signs can be very discreet especially at the onset of disease: poor performance in racing or sport horses, abnormal breathlessness or prolonged recovery. When the condition is more severe, an intermittent cough can occur. But unlike RAO, IAD does not cause marked clinical signs at rest: no respiratory distress nor deep cough.
Causes of IAD
Prehistoric horses used to be wild and live in the open air eating grass 18h a day. Domesticated horses we know today have a completely different lifestyle: most live inside stalls with suboptimal ventilation, on straw bedding, and are fed dry hay. The respiratory system of the horse has yet not adapted to this new environment and the dust that goes with it. Dust is essentially made of a mixture of plant and bacteria fragments (some bacterial fragments named endotoxins are extremely irritant), mould and mould fragments (Aspergillus, Penicillium, Mucor, Alternaria, etc.).
Dust particles are of variable size. Respirable particles (less than 5 micrometers in diameter) are able to be inhaled down to the deepest parts of the lungs, in the bronchioles and alveoli. In an ordinary stable, each millilitre of air contains about 3000 respirable particles. With each inspiration, a horse thus inspires…12 million respirable particles!
These little particles trigger a protective response of the lungs. In some horses, this reaction is exacerbated and induces an increased production of mucus, a thickening of the mucosa (the thin cell layer that covers the inside of the airways and the lungs) and a broncho constriction (reflex contraction of the smooth muscles around the airways that reduces the air passage diameter).
How to Diagnose ADI
How to treat IAD
Eliminate the dust!
IAD, as RAO, is closely linked to the environment. Thus, its management must imperatively include measures to reduce dust in the breathing environment of the horse. Otherwise, symptoms are bound to reappear as soon as the medical treatment is finished. To reduce dust in the environment, simple measures are recommended: replace straw bedding by dust-free wood shavings, eliminate dry hay and replace it by sterilised hay or good quality haylage, increase ventilation in the stall and the stable in general, take the stocks of hay and straw out of the stable and put them in a clean and dry place, protected from the rain, take the horse out in a field or a paddock regularly, etc.
A new name for IAD
Author : DAUVILLIER Julie, Veterinary
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