Randomized clinical trial to assess the effect of antibiotic therapy on health and growth of preweaned dairy calves diagnosed with respiratory disease using respiratory scoring and lung ultrasound

摘要

The primary objective of this randomized field studywas to assess the effect of antibiotic therapy on healthand growth of preweaned dairy calves diagnosed withnaturally occurring respiratory disease, using respiratoryscoring and portable lung ultrasound. A secondaryobjective was to determine whether treatment responsedepended on clinical presentation at the time of diagnosis.Holstein calves (n = 357) were enrolled at 3to 6 d of age and followed until 52 d on 2 commercialdairies. Calves were examined twice weekly by blindedmembers of the research team. Clinical respiratory andultrasonographic lung scores were assigned at eachexam and used to classify the first detected respiratorydisease event (BRD1) into upper respiratory tract disease(clinical, no significant consolidation); subclinicallobular pneumonia (not clinical, patchy consolidation≥1 cm~2); clinical lobular pneumonia (clinical, patchyconsolidation ≥1 cm~2); subclinical lobar pneumonia(not clinical, ≥1 lobe consolidated); and clinical lobarpneumonia (clinical, ≥1 lobe consolidated). At BRD1,calves were blocked by their respiratory disease statusand randomized to receive an antibiotic (tulathromycin,2.5 mg/kg subcutaneous) or placebo (sterile saline,equal volume subcutaneous). Multivariable linear andlogistic regression analyses were used to model responseto therapy. At BRD1 (n = 289), the distribution of diagnoseswas 29% (upper respiratory tract disease), 43%(subclinical lobular pneumonia), 13% (clinical lobularpneumonia), 8% (subclinical lobar pneumonia), and7% (clinical lobar pneumonia). Early antibiotic therapylimited progression of lung consolidation immediatelyfollowing treatment, reduced the likelihood of requiringtreatment within 7 d of BRD1, and improved growthand mortality before weaning. Despite receiving multipledoses of antibiotics after BRD1, calves treatedwith either antibiotic or placebo were equally likelyto enter the weaning phase with pneumonia. Clinicalpresentation was associated with response to treatmentfor worsening of consolidation, early treatment failure,days to retreatment, and average daily gain. Overall,treatment was associated with short-term benefits, butmore research is needed to develop treatment protocolsthat more effectively treat pneumonia and ensure thatcalves enter the weaning period with ultrasonographicallyclean lungs.