Association of submaximal exercise test variables with diagnosis of asthma in a mixed-breed cohort of leisure horses.

BACKGROUND: Submaximal exercise tests (SET) are used to assess respiratory health in various contexts. The diagnostic value of SETs for the assessment of asthma in the field remains uncertain. HYPOTHESIS/OBJECTIVES: A SET helps distinguish healthy horses and asthma phenotypes. ANIMALS: Twenty-six privately owned mixed-breed leisure horses of a clinical cohort. Horses were healthy (8) or diagnosed with mild (miEA) (4), moderate (modEA) (7), or severe asthma (sEA) (7) according to history, clinical examination, and bronchoalveolar lavage fluid (BALF) cytology. METHODS: Cross-sectional study using clinical data and samples from a hospital cohort. The SET included ECG, arterial blood gas, lactate, respiratory rate (RR), and heart rate (HR) analysis. Samples were taken at rest (time point (T) 0), and after defined intervals (twice 2 minutes trot (T1, T2) and gallop (T3, T4), followed by 3 minutes trot (T5) and gallop (T6)). HR and RR recovery were evaluated. Predictive values of variables towards diagnosis of asthma were estimated with ordinal models. RESULTS: Arterial partial pressure of oxygen (pO2) at T0 had the strongest association with diagnosis (τ = -.513, LRT = 18.1, adj. P < .001). Hypoxemia at T6 was evident in all healthy and miEA horses. In contrast, some horses with modEA and sEA presented with increased pO2 at T6 compared to T0. Recovery lengths had no significant association with diagnosis (RR τ = .112, LRT = .805, adj. P = .493; HR τ = .174, LRT = 1.528, adj. P = .287) and demonstrated wide intra-group variation. CONCLUSIONS AND CLINICAL IMPORTANCE: The SET did neither confirm diagnosis of asthma nor provide adequate results to assess respiratory health or disease in this cohort.