Differentiating airway inflammation in calves based on cluster analysis of bronchoalveolar lavage fluid cytology

Abstract

Background: Nonbronchoscopic bronchoalveolar lavage (nBAL) is routinely performed in calves, and airway cytology has great potential in airway disease diagnostics. A good reference framework for nBAL cytology is lacking. Objectives: To distinguish different cytological profiles in nBAL from grouped housed calves using cluster analysis, and characterize these profiles on individual and herd levels. Animals: Three hundred thirty-eight group-housed calves from 60 herds (mainly dairy and beef). Methods: Cross-sectional study. Differential counts of white blood cells were determined on nBAL fluid, followed by differentiation of cytological profiles by K-means-based cluster analysis. These profiles were characterized by reference values, decision tree analysis, and associations with clinical, ultrasonographic, bacteriological, and cytological features. Results: A normal (55.9%), a neutrophilic (41.1%), and an eosinophilic profile (3.0%) were identified. The normal profile was characterized by reference values of 2.3% to 47.4% neutrophils, 35.1% to 95.1% macrophages, 0.4 to 22.9% lymphocytes, and 0.0% to 0.9% eosinophils. The neutrophilic profile was characterized by ≥44.5% neutrophils, <1.6% eosinophils, and <11.5% lymphocytes. This profile was associated with the isolation of Pasteurella multocida, the presence of neutrophils with toxic granulation, and the presence of phagocytosed bacteria in neutrophils. The eosinophilic profile was characterized by eosinophils ≥1.6% (neutrophilia present) or ≥2.4% (neutrophilia absent), and associated with the presence of mast cells. On herd level, the neutrophilic and eosinophilic profiles were present in 85.0% and 15.0% of the herds, respectively. Conclusions and Clinical Importance: This study provides a first step in the development of cytological guidelines, aiding the assessment of airway health and inflammation in calves through nBAL fluid cytology.