33rd Annual Scientific Meeting proceedings

Introduction
To describe an unreported exercise-induced disorder of the epiglottis associated with poll flexion in harness racehorses.

Materials And Methods
Medical records of harness racehorses that presented for exercising upper respiratory tract (URT) endoscopy between 2005 and 2022 were reviewed. All horses were exercised on a high-speed treadmill with alternating one-minute phases of free head carriage (no rein tension on the bit) and poll flexion (driven onto the bit with long reins). Tracheal airway pressure measurements were additionally obtained between 2018 and 2022.

Results
Seven Standardbreds and 11 Norwegian-Swedish Coldblooded trotters were diagnosed with unilateral or bilateral compression of the epiglottis during exercise in poll flexion. These horses demonstrated this disorder during the first phase of induced poll flexion, prior to visual appearance of any other exercise-induced URT disorders. Tracheal inspiratory pressures available in affected horses were more negative than the normal variation in harness racehorses.

Discussion/conclusions
Exercise-induced compression of the epiglottis during poll flexion in harness racehorses is a primary URT disorder evident during periods of poll flexion. This compression seems to be initiated by the hyoid apparatus compressing the lateral nasopharyngeal walls and base of the epiglottis inwards during poll flexion. Exercise-induced compression of the epiglottis during poll flexion causes mild to moderate inspiratory URT obstruction as evidenced by tracheal pressure measurements. The current treatment recommendation is to limit the degree of poll flexion by use of tack modifications.