Factors associated with lung cytology as obtained by non-endoscopic broncho-alveolar lavage in group-housed calves

BACKGROUND: Respiratory infections are the main indication for antimicrobial use in calves. As in humans and horses, studying inflammation of the deep airways by lung cytology raises the possibility of preventing respiratory disease and targeting its treatment in the future. Whether lung cytology findings coincide with clinical signs and lung ultrasonographic findings is currently unknown. Therefore, the objective of the present study was to determine the association of lung cytology with clinical signs, lung consolidation and broncho-alveolar lavage fluid (BALf) characteristics (including bacteriology). A total of 352 indoor group-housed calves aged between 1 and 6 months from 62 conveniently selected commercial herds were included in this cross-sectional study. Clinical examination, thoracic ultrasound and bacteriology and cytology on non-endoscopic broncho-alveolar lavage (nBAL) samples were performed. RESULTS: Pneumonia, defined as presence of ultrasonographic lung consolidations ≥1 cm in depth, affected 42.4% of the calves. Mean BALf neutrophil percentage was 36.6% (SD 23.8; R 0–97.4) and only a positive induced tracheal cough reflex (P = 0.04), standing posture (P = 0.03) increased breathing rate (P = 0.02) and isolation of Pasteurella multocida (P = 0.005), were associated with increased neutrophil percentage. No significant associations between lung ultrasonographic findings and cytology results were present, except for presence of basophils in BALf and consolidation of > 3 cm in depth (OR = 2.6; CI = 1.2–5.6; P = 0.01). Abnormal lung sounds were associated with detection of eosinophils in BALf (OR = 2.8; CI = 1.0–8.1; P = 0.05). Total nucleated cell count (TNCC) (P < 0.001) was positively and macrophage percentage (P = 0.02) negatively associated with volume of lavage fluid recovered. Macroscopic blood staining of BALf increased TNCC (P = 0.002) and lymphocyte percentage (P = 0.001). CONCLUSIONS: Only a limited number of clinical signs and ultrasonographic findings were associated with nBAL cytology. BALf cytology offers additional and distinct information in calves aiding in detection and prevention of respiratory conditions. In this population, selected from herds not reporting any recent respiratory illness, a high number of calves had ultrasonographic lung consolidation and high neutrophil percentage in BALf, suggesting that subclinical disease presentations frequently occur.