Unilateral and bilateral compression of the epiglottis during poll flexion in harness racehorses

Abstract

SummaryBackgroundHorses exercised ‘onto the bit’ with periods of induced poll flexion can demonstrate a unique array of upper respiratory tract (URT) disorders.ObjectivesTo describe a previously unreported exercise‐related disorder of the epiglottis associated with poll flexion in harness racehorses.Study designRetrospective observational study.MethodsMedical records of all harness racehorses that presented for exercising URT endoscopy between 2005 and 2022 were reviewed. These horses were exercised on a high‐speed treadmill using a previously standardised protocol with alternating 1‐min phases of free head carriage (no rein tension on the bit) and poll flexion (driven onto the bit with long reins) until they could no longer maintain the trotting gait.ResultsSeven 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 progression of this disorder during the phases of induced poll flexion and showed no signs of epiglottic compression during phases exercised with free head carriage.Main limitationsRetrospective nature of study and limited sample size due to low prevalence.ConclusionsExercise‐related compression of the base of the epiglottis is a URT disorder only evident videoendoscopically when horses are driven onto the bit leading to poll flexion. It is most often seen in association with dynamic laryngeal collapse but can also be witnessed as a solitary disorder. Videoendoscopically, it appears that the compression is initiated by the rostral advancement of the larynx and hyoid apparatus within a progressively narrowing intermandibular space during poll flexion. Visually, this leads to local inward compression of the lateral nasopharyngeal walls and base of the epiglottis. Further studies are ongoing to confirm this hypothesis and to objectively quantify the degree of URT obstruction caused by this conformational narrowing of the epiglottis during poll flexion.