Prevalence of pharyngeal and laryngeal abnormalities in Thoroughbreds racing in Australia, and their association with performance.

REASONS FOR PERFORMING STUDY: Little information is available regarding the prevalence of abnormalities of the upper airway and their association with performance in the general population of Thoroughbred racehorses. OBJECTIVES: To describe the prevalence of selected abnormalities of the upper airway and their association with performance in Thoroughbred racehorses in Australia. HYPOTHESIS: That abnormalities of the upper airway of Thoroughbred racehorses are associated with poor race performance. METHODS: Rhinolaryngoscopy was performed after racing and presence and characteristics of abnormalities of the larynx and pharynx were recorded in a prospective cross-sectional study of Thoroughbred horses racing in Victoria, Australia. RESULTS: Rhinolaryngoscopy was performed once on each of 744 horses over 35 months. Fifty abnormalities of the upper airway were detected in 47 horses (6.3%, 95% confidence interval [CI] 4.7-83%). Epiglottic entrapment was detected in 7 horses (0.9%, 95% CI 0.4-1.9%) and was significantly (P = 0.015) associated with superior performance. Grade 2 asymmetry (4 grade scale) of the left arytenoid cartilage was detected in 9 horses (1.2%, 95% CI 0.5-2.4%) and was also associated with superior performance (P<0.001). Ulceration or erosion of the mucosa of the axial surface of one or both arytenoids was detected in 18 horses (2.4%, 95% CI 13-3.8%) and was not associated with alterations in exercise performance (P = 0.31). CONCLUSIONS: Epiglottic entrapment, Grade 2 laryngeal asymmetry and mucosal erosions detected in Thoroughbred racehorses were not associated with impaired performance; therefore, surgical correction and concern over laryngeal function in horses with Grade 2 asymmetry may not be necessary in individuals performing to expectation.

Risk factors for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: Risk factors for occult exercise-induced pulmonary haemorrhage (EIPH) are poorly defined or quantified. OBJECTIVES: To investigate the importance of putative risk factors for EIPH amongst Thoroughbred racehorses in Australia. METHODS: Tracheobronchoscopy was used to determine EIPH status of 744 Thoroughbred racehorses after flat racing in Melbourne, Australia. Horses were identified for study before racing, and over 50% of horses racing during the study period were examined. Statistical analysis included use of bivariate and multivariate logistic regression analysis to account for simultaneous effects of a large number of variables. RESULTS: The only risk factor identified as associated with both EIPH ≥ 1 or ≥ 2 was ambient temperature, with horses racing at temperatures <20 °C being at ∼ 2 times risk of occult EIPH. There was no association of EIPH with age, sex, weight carried, track hardness, speed of racing, or air quality. CONCLUSIONS: There do not appear to be individual risk factors, amongst those examined in this study, that are strongly associated with EIPH. POTENTIAL RELEVANCE: The risk of developing EIPH cannot be readily determined from a combination of age, race speed, race distance, track hardness or air quality. This study does not provide support for the hypotheses that racing on hard surfaces or in polluted air contributes to the development of EIPH.