Study population
The study included 90 French Standardbred racehorses in active training, sampled between October 2020 and January 2023; and 84 horses referred to the hospital between February 2021 and May 2023 for decreased performance and/or respiratory disease. Minimal sample size was estimated at 92 horses (Epi InfoTM, Cohort and cross-sectional study statistical calculator) in order to be able to detect a significant odd ratio of 3.5. Data concerning housing conditions (indoor/outdoor), bedding (straw, wood shavings), hay forage (dry/soaked/steamed), activity (training/resting), occurrence of poor performance or exercise intolerance, as well as reported respiratory clinical signs (cough, dyspnea, nasal discharge, noise during exercise, increased respiratory effort at rest, epistaxis), were collected. Horses that had received corticotherapy or antimicrobial medication within the two weeks before examination were not included in the study. Horses with signs of systemic illness, other causes of decreased performance or other respiratory pathologies than equine asthma were excluded. The study was approved by the regional Animal Ethic Committee (CERVO-2020-3-V).
Horses were sampled at least 24 hours after the last training or race. Each horse was submitted to a thorough clinical examination by an ECEIM diplomate or resident. If observed, the presence of cough, nasal discharge, nostril flaring at rest, or dyspnea was recorded. Rebreathing pulmonary auscultation was performed and abnormal pulmonary (wheezes/crackles) or tracheal sounds, induction of cough, and delayed recovery following removal of the rebreathing bag were recorded. Venous blood samples were collected for hematology, and additional biochemical analysis when judged clinically necessary.