Summary:The frequencies of dynamic obstructions in thoroughbreds were investigated by performing on-board exercise endoscopy in 135 horses. 17 of these horses showed abnormal respiratory noise only and 35 solely poor performance. In 39 cases, both was reported. In addition, 44 horses underwent endoscopy without any clinical signs. In all of 56 horses that exhibited an audible abnormal respiratory noise, an obstruction of the upper respiratory tract was present. Overall, dynamic upper airway obstructions were detected in 72.6 % (98/135). The most commonly diagnosed obstruction was axial deviation of the aryepiglottic fold (ADAF) in 55.1% of horses (54/98). 24.4 % (24/98) showed palatal instability (PI), 30.6 % (30/98) dorsal displacement of the soft palate (DDSP) and 11.2 % (11/98) arytenoid cartilage collapse (ACC). Furthermore, 53.1% (52/98) of horses had abnormalities in the area of the vocal folds. Of these horses, 13 had unilateral or bilateral vocal cord collapse (VCC) and 8 displayed vibration of the vocal cords. 31 horses showed axial deviation in the area of the caudal vocal fold (ADPV) as a sole abnormality. By the new description of these ADPV, the origin of the abnormal respiratory noise in a further proportion of horses could be explained. Including ADPV, an obstruction of the upper airways was observed in all horses (100 %) with specified abnormal respiratory noise. If only horses with long or continuous (> 8 sec) DDSP were taken into account, abnormal respiratory noise was audible in 93.3 % and poor performance was present in 73.3 %. It can thus be assumed that horses with DDSP requiring treatment are clinically apparent either with abnormal respiratory noise or poor performance. Furthermore, it was demonstrated, that in 52.3% of horses without poor performance or abnormal respiratory noise an dynamic upper airway obstruction was identified.
The progression of dynamic obstructions of the upper respiratory tract in Thoroughbreds was examined by performing on-board exercise endoscopy during fast work on 135 horses. Exercise endoscopy was performed on horses with and without abnormal respiratory noise and with and without a history of poor performance. For classification, the exercise was divided into three equal sections. 54.8 % (74 horses) of the 135 horses examined had a history of poor performance; only 1.5 % at the beginning of fast work and 35.5 % at maximum performance. At the beginning of fast work, abnormal respiratory noise was audible in 8 horses (5.9 %), shortly before the end of training in 55 horses (40.7 %). A marked increase in the number of affected horses of each dysfunction among the horses with obstructions in the area of the upper respiratory tract could be observed with increasing performance. Some obstructions only occurred during higher performance levels. It could be demonstrated in which phase during horses' training obstructions occurred with or without having effect on the performance. The assessment of ACC showed which grade of ACC causes a negative impact on horses' performance in the different stages of exercise. As there is a high probability of poor performance at least during races with ACC of grade B3 or higher, treatment options can already be discussed here. As DDSP mainly occurs during maximum performance, it can only be definitely excluded if the horse is exercised to maximum performance during endoscopy. The evaluation method used in this study allows a better analysis of the effect of dysfunctions on each horse's performance, even if multiple obstructions occur.
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