Thoracic Ultrasonography Findings and Their Association With Respiratory Pathogens in 221 Young Beef Cattle at Fattening Farms: A Cross‐Sectional Study

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anglais. ABSTRACT Background Thoracic ultrasonography (TUS) could improve antibiotic treatment selection in cattle with respiratory diseases. Hypothesis/Objectives Evaluate the association between respiratory pathogens and consolidations on TUS in feedlot cattle, at both individual and group levels. Animals A total of 221 bulls, aged 8.8 months and weighing 322.5 ± 160 kg, from nine farms. Methods Cross‐sectional study including all data from clinical examinations and TUS collected weekly during the first month on feed. Pathogens were assessed by seroconversion (all animals) and qPCR on nasal swabs (sick animals). At the individual level, the association between pathogen detection and TUS consolidation was investigated using univariate logistic regression, and the ability of consolidation size to differentiate bacterial from non‐bacterial pneumonia was assessed using receiver operating characteristic curves. Principal component analysis identified clusters at the group level based on pathogen detection and TUS results. Results At the individual level, bulls infected with multiple pathogens (odds ratio [OR], 8.1; 95% confidence interval [CI], 2.21–29.8) or a single virus (OR, 5.49; 95% CI, 1.42–21.3) were more likely to have consolidations than those not infected. A total consolidation size > 14 cm 2 in the scanned thoracic region differentiated bacterial from non‐bacterial pneumonia with a sensitivity of 47.8% (95% CI, 36.4–83.3) and specificity of 94.1% (95% CI, 60.0–100.0). These results were consistent at the group level; clustering based on bacterial versus non‐bacterial etiology correlated with the number and size of consolidations. Conclusions and Clinical Importance Consolidation size could help differentiate bacterial from non‐bacterial pneumonia, guiding treatment at both individual and group levels.