Researchers have proven that anomalies of the equine upper respiratory tract, such as left laryngeal hemiplegia (roaring) and dorsal displacement of the soft palate, negatively impact performance. But alterations in normal airway structure and function can occur at any point along the respiratory tract, even beyond the larynx, within the depths of the lung, or hidden beyond the probing tip of the veterinarian's endoscope. While heaves (recurrent airway obstruction, formerly known as chronic obstructive pulmonary disease), is a very familiar and severe condition of the lower respiratory tract in older horses, inflammatory airway disease (IAD)–a low-grade inflammatory syndrome of the airways in younger horses–is less commonly recognized.

Despite its apparently taciturn nature, IAD is thought to be a ubiquitous and important performance-limiting condition of the lower respiratory tract in the young and otherwise healthy athletic horse.

"While the exact prevalence of IAD in athletic horses is unknown, it is suspected that IAD is an important contributor to exercise intolerance and poor performance in horses," explains Susan Holcombe, VMD, PhD, Dipl. ACVS, ACVECC (emergency and critical care), an associate professor at Michigan State University's (MSU) College of Veterinary Medicine