By Nancy S. Loving, DVM
Not too long ago, heaves was more commonly referred to as chronic obstructive pulmonary
disease, or COPD. In recent years, the terminology has changed to distinguish the equine
from the human form of lower airway disease. In humans, COPD refers to a fairly
non-reversible and persistent obstruction of the lower airways, mostly related to smoking.
Since horses don’t smoke and their lower airway obstruction bouts tend to be intermittent
and recurrent, a new moniker was formed, one that is more fitting to describe the disease
process in horses: recurrent airway obstruction, or RAO. This syndrome refers to episodic
events of over-reactivity, inflammation, bronchoconstriction and obstruction of the lower
airways, particularly as triggered by exposure to environmental pollutants, such as dust
and moldy hay. In most cases, this lower airway inflammation responds well to medical
therapy with bronchodilator drugs.
Much like an asthmatic human, an affected horse experiences episodes that may come and
go, recurring relative to the amount of inhaled pollutants. Ultimately, there may be
permanent airway damage with some permanent degree of airway obstruction, but recurrent
attacks vary in degree and severity.
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