Medical causes of poor performance and their associations with fitness in Standardbred racehorses

Abstract

Background Poor performance is a multifactorial syndrome of racehorses, commonly associated with subclinical disorders, which can be diagnosed by exercise testing. Objectives Describe the prevalence of medical causes of poor performance in Standardbreds unassociated with lameness, and evaluate their relationships with fitness variables measured by exercise treadmill test. Animals Hospital population of 259 nonlame Standardbred trotters referred for poor performance. Methods The horses' medical records were retrospectively reviewed. Horses underwent a diagnostic protocol including resting examination, plasma lactate concentration, treadmill test with continuous ECG and assessment of fitness variables, creatine kinase activity, treadmill endoscopy, postexercise tracheobronchoscopy, bronchoalveolar lavage (BAL), and gastroscopy. The prevalence of different disorders was evaluated, including cardiac arrhythmias, exertional myopathies, dynamic upper airway obstructions (DUAOs), exercise‐induced pulmonary hemorrhage (EIPH), moderate equine asthma (MEA), and gastric ulcers (EGUS). The associations of these disorders with fitness variables were investigated individually and using multivariable models. Results Moderate equine asthma and EGUS were the most common disorders, followed by EIPH, DUAOs, cardiac arrhythmias, and exertional myopathies. Hemosiderin score was positively correlated with BAL neutrophils, eosinophils, and mast cells; increased creatine kinase activity was associated with BAL neutrophilia, DUAOs, premature complexes, and squamous gastric disease. Treadmill velocity at a plasma lactate concentration of 4 mmol/L and at heart rate of 200 beats per minute was negatively affected by BAL neutrophilia, multiple DUAOs, exertional myopathies, and squamous gastric disease. Conclusions The multifactorial nature of poor performance was confirmed, with MEA, DUAOs, myopathies and EGUS representing the main diseases involved in fitness impairment.

Associations between postrace atrial fibrillation and measures of performance, racing history and airway disease in horses

“…An association between AF and EIPH has long been suspected, and epistaxis has been reported as a common presenting complaint in horses with AF. 27 A previous study of thoroughbreds did not find an association between epistaxis and AF on race day. 3 However, epistaxis is infrequent, and this association would be difficult to establish because of low study power.…”

“…Despite these limitations, a high incidence of severe EIPH was observed in horses with AF. An association between AF and EIPH has long been suspected, and epistaxis has been reported as a common presenting complaint in horses with AF 27 . A previous study of thoroughbreds did not find an association between epistaxis and AF on race day 3 .…”

“…In Japanese thoroughbreds, it was found that older age and turf racing were associated with incident AF 3 . In standardbred racehorses, 1 study found age to be a risk factor for AF development, 2 whereas another study found no association between age and frequency of cardiac arrhythmias 27 . Based on these studies, high volumes of strenuous exercise might promote AF in horses.…”

“…However, conflicting results are reported regarding the relationship between cardiac arrhythmias and upper and lower airway disease, with 1 study finding that upper airway abnormalities were associated with arrhythmias 32 and another study finding no association with arrhythmias and either upper or lower airway disease 31 . In horses presented to the hospital with AF, exercise intolerance was the most commonly reported sign, followed by dyspnea and epistaxis 27 . However, an association between epistaxis, presumably caused by severe exercise‐induced pulmonary hemorrhage (EIPH), and AF has not been clearly shown 3 .…”

“…31 In horses presented to the hospital with AF, exercise intolerance was the most commonly reported sign, followed by dyspnea and epistaxis. 27 However, an association between epistaxis, presumably caused by severe exercise-induced pulmonary hemorrhage (EIPH), and AF has not been clearly shown. 3 Endoscopy is a sensitive test for EIPH and tracheal mucus accumulation (TMA) and can aid in the diagnosis of lower airway disease.…”