Owner-reported coughing and nasal discharge are associated with clinical findings, arterial oxygen tension, mucus score and bronchoprovocation in horses with recurrent airway obstruction in a field setting

Abstract

Reasons for performing study: In clinical practice, veterinarians often depend on owner-reported signs to assess the clinical course of horses with recurrent airway obstruction (RAO).

Objectives: To test whether owner-reported information on frequency of coughing and observation of nasal discharge are associated with clinical, cytological and bronchoprovocation findings in RAO-affected horses in nonstandardised field conditions.

Study design: Cross-sectional study comparing healthy and RAO-affected horses.

Methods: Twenty-eight healthy and 34 RAO-affected Swiss Warmblood horses were grouped according to owner-reported 'coughing frequency' and 'nasal discharge'. Differences between these groups were examined using clinical examination, blood gas analyses, endoscopic mucus scores, cytology of tracheobronchial secretion and bronchoalveolar lavage fluid, and airway hyperresponsiveness determined by plethysmography with histamine bronchoprovocation.

Results: Frequently coughing horses differed most markedly from healthy control animals. Histamine bronchoprovocation-derived parameters were significantly different between the healthy control group and all RAO groups. Mucus grades and tracheobronchial secretion and bronchoalveolar lavage fluid neutrophil percentages had particularly high variability, with overlap of findings between groups. Owner satisfaction with the clinical status of the horse was high, even in severely affected horses.

Conclusions: Owner-reported coughing and nasal discharge are associated with specific clinical and diagnostic findings in RAO-affected horses in field settings. While airway hyperresponsiveness differentiates best between healthy horses and asymptomatic RAO-affected horses, the absence of coughing and nasal discharge does not rule out significant neutrophilic airway inflammation. Owner satisfaction with the clinical status of the horse was uninformative.

Keywords: airway hyperresponsiveness; clinical signs; histamine; horse; lower airway disease; lung function.