Association between cough and cytology of bronchoalveolar lavage fluid and pulmonary function in horses diagnosed with inflammatory airway disease

Background: The objective of this study was to examine the relationship between chronic cough, pulmonary mechanical function, bronchial hyper-responsiveness, and peripheral airway inflammation in adult performance horses with nonseptic inflammatory airway disease (IAD). Hypothesis: We hypothesized that horses with a presenting complaint of cough have a higher percentage of inflammatory cells on bronchoalveolar lavage (BAL), greater airway obstruction, and airway hyper-responsiveness (AHR) than do horses without cough. Animals/Sample Population: Adult performance horses (n = 137) referred for evaluation of signs of IAD including cough or exercise intolerance (university hospital patients) and BAL samples (n = 142) taken in first opinion practice. Methods: A descriptive, retrospective cohort analysis was performed to evaluate the association between chronic cough and pulmonary mechanical function, AHR. BAL cytology, patient signalment, and comorbid features (multivatiable logistic regression). Results: Cough was significantly more prevalent in horses > 7 years, and best characterized by a high BAL neutrophil count (> 5%) and nasal discharge. Lung function mechanics, abnormal thoracic auscultation, and exercise intolerance did not retain statistical significance in the logistical regression analysis of cough. Although AHR was not related to neutrophilic airway inflammation (BAL neutrophils > 5%), it was significantly associated with BAL mast cells > 2%. Conclusions and Clinical Importance: Our data support that neutrophilic airway inflammation may potentiate cough without further changing respiratory mechanical function in IAD. In contrast, mast cell release increased AHR without affecting the incidence of cough. Cough may be used as an indicator of neutrophilic airway inflammation in the presence of low-grade nonseptic respiratory disease.