Longitudinal dynamics and recovery of lung ultrasonographic consolidations, association with growth in dairy calves in herds with circulating bovine coronavirus and Pasteurellaceae

Subclinical pneumonia is frequently detected in calves; however, its longitudinal dynamics, including recovery during the neonatal period, remain poorly understood. This prospective cohort study characterized lung consolidation dynamics, recovery, and growth in dairy calves from 2 herds with circulating bovine coronavirus (BCoV) and Pasteurellaceae. A total of 126 newborn calves from 2 dairy herds were monitored using quick thoracic ultrasonography and clinical scoring, with examinations performed twice weekly until one month of age. Based on anatomical landmarks, the lung was divided into 4 quadrants for ultrasonographic evaluation. Lung ultrasound scores (LUS) were defined as 0 (consolidations < 1 cm in depth), 1 (≥1 to < 2 cm), 2 (≥2 to ≤ 3 cm), and 3 (>3 cm), based on the most severe lesion across quadrants; calves with LUS 2 or 3 were treated. Recovery was defined as regression to LUS 0 within 3 subsequent visits. Calves were weighed at birth and at 1 and 2 mo using an electronic scale; however, in Farm 2, body weight at 2 mo was estimated using a weight tape. Average daily gain (ADG) during the first and second month were calculated. Pathogen testing for the 9 most common respiratory agents was performed using real-time PCR. All calves developed lung consolidations of some extent during the first month of life. Overall, 74.6% of calves developed consolidations ≥ 1 cm (LUS >0) at a median age of 16 d; among affected calves, 97% had subclinical and 3% clinical pneumonia, with maximum LUS scores of 1 (n = 21), 2 (n = 51) and 3 (n = 22). During the first month, consolidations ≥ 1 cm affected one lung quadrant in 33.0% of calves, 2 in 38.3%, 3 in 23.4%, and all 4 in 5.3%. Circulation of BCoV and Pasteurellaceae was confirmed at herd level. Among untreated calves that developed LUS 1 (n = 46), 60.9% progressed to higher LUS scores. Antimicrobial treatment increased recovery odds in LUS 2 (OR = 3.6, 95% confidence interval (CI) 1.3; 9.9) and LUS 3 calves (OR = 28.9, 95% CI 3.0; 276.4) compared with untreated LUS 1 calves. Calves with 3 or 4 affected lung quadrants grew 87 g/day less during the first month (95% CI -182.0; 7.1), and calves with LUS >0 at 2 visits grew 61 g/day less from birth to 2 mo (95% CI -121.2; -0.4). Subclinical pneumonia was widespread during the first month of life in herds with circulating BCoV and Pasteurellaceae, with lung consolidations detected in all calves. Untreated LUS 1 lesions frequently progressed and seldom resolved spontaneously. Early detection and antimicrobial treatment of consolidations ≥ 2 cm improved recovery, whereas recurrent or multilobar lesions tended to compromise growth.