INTRODUCTION
Exercise-induced upper respiratory tract (URT) disorders are a common
cause of poor performance and abnormal respiratory noise at exercise in
sport horses and racehorses (Morris & Seeherman 1991; Kannegieter &
Dore 1995; Lane et al. 2006; Davidson et al. 2011; Strand et al. 2012).
The literature suggests a breed, gait and sporting discipline difference
in the prevalence (Kannegieter & Dore 1995; Tan et al. 2005; Strand et
al. 2012) and predisposition (Strand et al. 2012) to different forms of
URT disorders. Certain disorders appear to have a phenotypic
(conformational) cause, especially in horses where poll flexion is
induced, such as in harness racehorses (Fjordbakk et al. 2008; Strand et
al. 2012; Velie et al. 2020). Harness racehorses, along with draft
horses, dressage horses and gaited horses can also demonstrate a unique
array of exercise-induced URT disorders only during poll flexion
compared to horses not examined or exercised in this manner
(Hanche-Olsen et al. 2010; Allen et al. 2011; McCarrel & Woodie 2015;
Hackett & Leise 2018; Joó et al. 2021).
Exercise-related laryngeal disorders associated with poll flexion are
often induced by changes in the relative positioning of the larynx and
hyoid apparatus within the intermandibular space (McCluskie et al. 2008;
Fjordbakk et al. 2013) and exacerbated by the increased negative
inspiratory pressures caused by narrowing of the pharyngeal/laryngeal
lumen width during poll flexion (Petsche et al. 1995; Strand et al.
2009), as predicted by the Bernoulli Principle and Venturi Effect. Upper
respiratory tract disorders evident during poll flexion can be primary
in nature (Strand et al. 2004) or secondary to the increased regional
airway pressure gradients occurring with other URT disorders (Strand &
Skjerve 2012) and/or surgical interventions that alter laryngeal and/or
hyoid conformation (Vermedal & Strand 2020).
Currently reported exercise-induced disorders of the epiglottis include
intermittent epiglottic entrapment (Morris & Seeherman 1991;
Kannegieter & Dore 1995; Tan et al. 2005), epiglottic retroversion (Tan
et al. 2005) and flaccid epiglottis (Strand et al. 2012; Strand &
Skjerve 2012). These are less commonly reported than other
exercise-induced disorders of the larynx and/or pharynx. There is sparse
literature regarding exercise-induced epiglottic disorders in the horse
in general and compression of the base of the epiglottis during poll
flexion has not, to the authors knowledge, been reported as an
exercise-induced URT disorder. Similar manifestations have been
mentioned in the literature, namely dynamically flaccid epiglottis or
dorsomedial deviation of the margins of the epiglottis, however in these
cases the epiglottic disorder occurred concurrent with or subsequent to
other URT disorders such as dynamic laryngeal collapse (DLC) associated
with poll flexion and/or medial deviation of the aryepiglottic folds
(MDAF) (Fjordbakk et al. 2008; Strand & Skjerve 2012; McCarrel &
Woodie 2015; Joó et al. 2021).
The aim of this study was to report a clinically specific URT disorder
involving the epiglottis, seen videoendoscopically only during periods
of exercise with induced poll flexion, in harness racehorses.