A retrospective study of bronchoalveolar lavage fluid analysis in barrel racing horses with exercise-induced pulmonary hemorrhage and asthma in Texas from 2016 to 2018

Highlights

• Few studies have evaluated both EIPH and asthma within a single equine population or in barrel racing horses.

• Bronchoalveolar lavage (BAL) can evaluate both diseases with a single sample collection.

• No statistical difference was found in the frequency of neutrophilia, eosinophilia, or mastocytosis on BAL results between groups

Abstract

Exercise-induced pulmonary hemorrhage (EIPH) and asthma in barrel racing horses is a common disease across the United States. Limited information is available on non-infectious respiratory diseases in this population, the interaction between these two diseases, and the occurrence of both EIPH and asthma in the horse. The purpose of this study was to evaluate the bronchoalveolar lavage (BAL) fluid cytological results of barrel racing horses with EIPH, asthma, or both. A retrospective study was conducted using the medical records of horses that presented with cough and decreased athletic performance and BAL results that met the criteria for inclusion. Data from 95 horses were included from a private practice referral hospital in Texas. No statistical difference was found in the frequency of neutrophilia, eosinophilia, or mastocytosis between diagnoses of EIPH, asthma, or concurrent diagnoses of EIPH and asthma. Bronchoalveolar lavage of horses suspected of EIPH is warranted to fully characterize the noninfectious respiratory disease of barrel racing horses.

Introduction

Non-infectious respiratory disease in performance horses remains costly and challenging to manage and has the capability to diminish the athletic capability of these horses. The negative effects on a performance career in horses diagnosed with exercise-induced pulmonary hemorrhage (EIPH) and equine asthma have been clearly documented in racehorses (Hinchcliff et al., 2015). In contrast, limited information is available on non-infectious respiratory diseases in barrel-racing horses, the interaction between EIPH and asthma, and the impact on the horse's performance (Gold et al., 2018; Léguillette et al., 2016; Newton and Wood, 2002).

EIPH can be diagnosed by visualization of active bleeding from the nares immediately following intense exercise, by upper airway endoscopic examination of the trachea, and by presence of hemosiderophages or frank blood in bronchioalveolar lavage (BAL) fluid (Hinchcliff et al., 2015). Equine asthma is diagnosed by BAL fluid cytological evaluation, and can be categorized by a variety of characteristics, including severity (inflammatory airway disease versus recurrent airway obstruction) or predominant cell type (mastocytic, neutrophilic, or eosinophilic) (Couëtil et al., 2016). Pulmonary function testing has a useful role in research; however, the applicability to clinical practice remains unclear and less accessible (Bond et al., 2018).

Few studies have evaluated both EIPH and asthma within a single equine population or temporally within an individual horse (da Silva et al., 2017). Both diseases are commonly found in performance horses and the proposed pathophysiology may be interconnected. The presence of blood in the lung may act as a local irritant and may induce an inflammatory response that is consistent with mild equine asthma (McKane and Slocombe, 2010; Sullivan and Hinchcliff, 2015). Bronchoconstriction due to the presence of an irritant leads to elevated intrapleural pressure and may increase the risk of EIPH (da Silva et al., 2017). Additionally, long-term exposure to an irritant (such as red blood cells secondary to EIPH) may result in scar tissue formation within the lung parenchyma, resulting in reduced tissue compliance and increased intrapleural pressure (da Silva et al., 2017).

Horses used in barrel-racing are predominately Quarter Horses, or Quarter Horse-related breeds, and race on frequent schedules (Stricklin, 1998). Races are short sprints in both indoor and outdoor sand arenas, and in Texas often at high environmental temperatures (100–110 °F), therefore potentially worsening the underlying asthma. Dust exposure found in arenas due to increased use, and high environmental temperatures have been shown to exacerbate airway inflammation in asthmatic horses (Bullone et al., 2016; Lühe et al., 2017; McGorum et al., 1998; Pirie et al., 2003; Wheeler et al., 2006).

Due to the presence of pulmonary inflammation and remodeling in both asthma and EIPH we hypothesized that no differences in the BAL fluid leukocyte composition would be found between the two diseases. The purpose of this retrospective study was to evaluate the BAL fluid cytology results of barrel racing horses in northern Texas with EIPH, asthma, or both diseases concurrently; and to evaluate the relationship between a previous history of EIPH and the development of non-infectious respiratory disease.