Characteristics of palatal instability inThoroughbred racehorses and their association with the development of dorsal displacement of the soft palate

Abstract

Two forms of dynamic upper respiratory tract obstruction affecting racehorses that involve the soft palate have been described: palatal instability (PI) and dorsal displacement of the soft palate (DDSP). Observation of DDSP is straightforward in that it is an all or nothing event, whereas observation of PI is subjective and interpretation may vary between clinicians. The aim of this study was to attempt to characterise PI and to investigate endoscopic features that precede DDSP. A retrospective study on the endoscopic observations of Thoroughbred racehorses referred for high-speed treadmill endoscopy was performed. Endoscopic observations were reviewed during the last 10 s of the exercise test or the last 10 s prior to DDSP. The degree of axial deviation of the aryepiglottic folds (ADAF), the conformation of the epiglottis, the conformation of the soft palate and the amount of obstruction of the rima glottidis by the soft palate (i.e. soft palate stability) were assessed. A total of 72 horses were included in this study, of which 7 showed no evidence of PI. Of the 65 horses with PI, 30 (46%) developed DDSP. There were significant associations between the stability of the soft palate, epiglottic conformation and ADAF. Furthermore, development of DDSP was associated with increased severity of PI and ADAF and with changes in epiglottic conformation. This study has characterised the endoscopic features associated with PI and identified certain characteristics that precede DDSP. These observations may assist veterinary surgeons in recognising PI and the prodromal signs of DDSP.