Training related risk factors for exercise induced pulmonary haemorrhage in British National Hunt racehorses

• Published in: Equine veterinary journal Vol. 54; no. 2; pp. 283 - 289
• Main Authors: McGilvray, Tegan A., Cardwell, Jacqueline M.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-03-2022
• Subjects: Animals; EIPH; Hemorrhage - etiology; Hemorrhage - veterinary; horse; Horse Diseases - etiology; Horses; Inflammation; Longitudinal Studies; Lung Diseases - etiology; Lung Diseases - veterinary; National Hunt; Physical Conditioning, Animal - adverse effects; Prospective Studies; racehorse; Risk Factors; horse; EIPH; National Hunt; racehorse
• ISSN: 0425-1644; 2042-3306
• DOI: 10.1111/evj.13448

Background
Exercise induced pulmonary haemorrhage (EIPH) is an important condition of horses performing high intensity exercise, with reported prevalence among racehorses of up to 95%, based on the detection of blood on tracheobronchoscopy. Previously identified risk factors include age, sex, season, race type, years spent in racing and lower airway inflammation.
Objectives
To estimate the prevalence of EIPH in British National Hunt racehorses as indicated by two outcome measures: presence of tracheal blood on tracheobronchoscopy, and presence of moderate‐large (significant) proportions of haemosiderophages in tracheal wash (TW) fluid; and to identify training‐related risk factors for these indicators of EIPH.
Study design
Prospective longitudinal study.
Methods
Data from tracheobronchoscopy and TW cytology were analysed using univariable and multivariable mixed‐effects logistic regression.
Results
1184 observations, from 177 horses, were analysed. The prevalence of tracheal blood was 7.2% (95%CI: 5.8, 8.8) and significant haemosiderophages in TW fluid was 36% (95%CI: 33.3, 38.8). Increased time in training was significantly associated with increased odds of EIPH. For each additional year spent in training the odds of tracheal blood and presence of significant proportions haemosiderophages increased approximately 1.5‐fold (OR = 1.5; 95%CI: 1.1‐2.0; P = .005; and OR = 1.5; 95%CI: 1.3, 1.8; P < .001, respectively). Current inflammation was associated with previous haemorrhage, but not current haemorrhage.
Main limitations
There are no standardised measures for quantification of TW cytological parameters for EIPH diagnosis. Few horses were examined following jumping. Recent racing dates were not included in analysis.
Conclusions
Increasing time in training was a risk factor for both indicators of EIPH. Current inflammation was associated with previous haemorrhage, but not current or future haemorrhage, suggesting that haemorrhage leads to inflammation but not that inflammation leads to haemorrhage. Overall, our findings are consistent with the capillary stress failure theory of EIPH. The development of standardised measures for TW cytological diagnosis of EIPH is warranted.