Dynamic Laryngeal Collapse – An Obscure Disease in an Obscure Breed?

Dynamic laryngeal collapse associated with poll flexion (DLC) is a performance-limiting obstructive disorder of the equine upper airway characterized by bilateral symmetric collapse of the vocal folds and arytenoid cartilages. DLC was first described in the Norwegian/Swedish Coldblooded trotter (NSCT) and is now considered the most common exercise-induced upper airway abnormality in this breed. Affected horses have a normal endoscopic appearance of the upper airway at rest and when exercised with neutral head carriage; however, endoscopic signs of DLC become evident shortly after inducing poll flexion.

Although the clinical characteristics of DLC are well described, the pathophysiology of this disorder has remained obscure for years. However, recent studies have shed some light on pathophysiological factors and a brief discussion of these are presented below.

There is little doubt that poll flexion is the triggering event for clinical signs in affected horses. A 12° decrease in head/neck angle coincided with endoscopic signs of DLC, resulting in a significant reduction in tracheal inspiratory pressures. This degree of poll flexion is considered to be within the range normally experienced by harness racehorses during training and racing. Conversely, endoscopic signs of DLC were alleviated and tracheal pressures remained within normal range when affected horses were fitted with an external device designed to limit poll flexion even when exercised in rein tension.  [...]