Dynamic pharyngeal collapse in racehorses
Article first published online: 10 JUN 2010
© 2006 EVJ Ltd
Equine Veterinary Journal
Special Issue: Proceedings of the 7th International Conference of Equine Exercise Physiology
Volume 38, Issue S36, pages 546–550, August 2006
How to Cite
BOYLE, A. G., . MARTIN, B. B., DAVIDSON, E. J., DURANDO, M. M. and BIRKS, E. K. (2006), Dynamic pharyngeal collapse in racehorses. Equine Veterinary Journal, 38: 546–550. doi: 10.1111/j.2042-3306.2006.tb05602.x
- Issue published online: 10 JUN 2010
- Article first published online: 10 JUN 2010
- nasopharyngeal collapse;
- poor performance;
- high-speed treadmill videoendoscopy;
Reason for performing study: Dynamic pharyngeal collapse (PC) is a condition seen in racehorses that can be career-ending.
Objectives: To characterise and grade PC and describe the effects of PC on athletic performance.
Methods: Medical records were reviewed for 828 horses, of which 49 (6%) records were identified as horses with a primary diagnosis of PC. Tapes of video-endoscopy of the pharynx during exercise were reviewed. Each video recording was assigned a grade (0–4) reflecting the degree of PC and a classification for severity of upper airway obstruction. Earnings per race prior to diagnosis of PC were compared to earnings per race after diagnosis of PC for all horses, as well as performance index (PI). Available exercising arterial blood gases were reviewed for horses with PC.
Results: There were 35 (80%) Thoroughbreds (TB), and 9 (20%) Standardbreds (STD). 32 (73%) had a history of making an upper respiratory noise. 4 (9%) grade 1 PC, 8 (18%) grade 2 PC, 26 (59%) grade 3 PC, and 6 (14%) grade 4 PC. Seven (16%) horses were classified as mild PC, 18 (41%) as low-moderate PC, 14 (32%) as high-moderate PC, and 5 (11%) as severe PC. Of 30 horses 11 had abnormally decreased PaO2 and 8 horses had abnormally elevated PaCO2. A significant decrease was found in earnings per race prediagnosis when compared to post diagnosis earnings per race in horses ≥4 years of age (P = 0.003). A significant decrease was also observed for earnings per race prediagnosis when compared to post diagnosis earnings per race in horses with grade 3 PC (P = 0.03) No significant differences were observed in PI before or after diagnosis of PC.
Conclusions: There was a trend for PC to be observed in more TB than STD, and more males than females compared to the general hospital population. Horses with PC significant had decreases in arterial oxygenation. Racing records after a diagnosis of PC in all horses ≥4 years of age suggesting that older horses have a guarded prognosis for continued success.
Potential relevance: This study provides a classification system for dynamic pharyngeal collapse and suggests that older racehorses (≥4 years of age) diagnosed with PC and all horses with grade 3 PC have a poor prognosis for return to previous level of performance.