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.

Keywords: equine exercise physiology; equine performance; equine sports medicine; poor performance; sport horses; treadmill test.

FIGURE 1

Box and whiskers graph representing postexercise serum creatine kinase (CK) activity in males (M) and females (F). The statistical significance is shown as ****P < .0001.

FIGURE 2

Box and whiskers graph representing V200, VLa4 and pHmin in horses with (pos) or without (neg) clinical signs of exertional myopathies. The statistical significance is shown as **P < .01.

FIGURE 3

Box and whiskers graph representing VLa4 and Lacmax in horses with no DUAO, mild DUAO, severe DUAO, and multiple DUAOs. The statistical significance is shown as *P < .05 and **P < .01.

FIGURE 4

Box and whiskers graph representing VLa4, Lacmax and Lac30 in horses with mixed MEA, neutrophilic MEA, and eosinophilic‐mastocytic (Eos‐Mast) MEA. The statistical significance is shown as *P < .05, **P < .01, and ***P < .001.