Mild to moderate haemorrhage was not associated with inferior race day performance in this population of Thoroughbred racehorses.

Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/evj.12458 This article is protected by copyright. All rights reserved. SummaryReason for performing the study: Ambient temperature has been identified as a risk factor for exercise-induced pulmonary haemorrhage (EIPH) in racing Thoroughbreds. This warranted a more expansive investigation of climatic conditions on the incidence and severity of EIPH. Accepted ArticleThis article is protected by copyright. All rights reserved.The impact of other variables, such as the type of bit used, tongue ties, and non-standard shoes, has not been reported and also warrant investigation. Objectives:To examine the effect of various climatic variables as contributing risk factors for EIPH. Other previously uninvestigated variables, as well as standard track and population factors will also be examined.Study Design: Cross-sectional study. Methods: Thoroughbred racehorses competing at metropolitan racetracks in Perth, WesternAustralia were examined, 30-200 minutes post race with tracheobronchoscopy. Examination took place at 48 race meetings over a 12-month period. Examinations were graded (0 to 4), independently by 2 experienced veterinarians. Univariable analyses were performed, and variables with a P<0.25 were entered into a multivariable logistic regression analysis. The analysis was performed twice using the presence of blood (EIPH grade 0 vs. grades ≥1) and EIPH grades ≤1 vs. EIPH grades ≥2 as dependent variables.Results: EIPH was diagnosed in 56.6% of observations. Lower ambient temperature was significantly associated with EIPH grades ≥1 (OR 0.95; 95% CI 0.93-0.98) and EIPH grades ≥2 (OR 0.97; 95% CI 0.94-1.0). Bar shoes were significantly associated with EIPH grades ≥1 (OR 6.35; 95% CI 2. 17-18.54) and EIPH grades ≥2 (OR 2.72 95% CI 1.3-5.68). Increasing race distance was significantly associated with EIPH grade ≥1, and increasing lifetime starts was significantly associated with EIPH grade ≥2.Conclusions: Ambient temperature is a risk factor for EIPH in Thoroughbred racehorses, with lower temperatures associated with increased risk. Bar shoes are a novel risk factor for EIPH in this population.

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Limiting the number of days in the current racing preparation and spacing races for horses with moderate to severe EIPH may be beneficial for reducing tracheobronchoscopic EIPH severity. The association between ambient temperature and EIPH warrants further investigation.