Thoracic ultrasound severity, not serum total protein, predicts short-term clinical recovery in preweaned dairy calves: A multifarm retrospective cohort

Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality in pre-weaned dairy calves, yet field-applicable prognostic tools for short-term treatment outcomes remain limited. The objective of this study was to evaluate whether calf thoracic ultrasound severity scoring (CFUS) at diagnosis or early-life serum total protein (STP) predicts failure of lesion resolution following antimicrobial therapy. A retrospective co­hort study was conducted across 8 commercial dairy farms in Ohio and Wisconsin (August 2022-November 2025). Calves di­agnosed with BRD via an abnormal lung score (CFUS ≥ 2) were treated per farm protocol. Clinical resolution was defined as a subsequent CFUS ≤ 1. Clinical failure included persistent le­sions (CFUS ≥ 2) or loss to follow-up due to death or culling. Of 1,779 enrolled calves, 1,200 (67.5%) achieved resolution and 579 (32.5%) experienced failure. Initial CFUS was strongly associ­ated with failure; each one-point increase in CFUS increased the risk of failure by 53% (risk ratio [RR] = 1.53; P < 0.01). Calves diag­nosed at their second examination (older age) had higher failure risk than those diagnosed at their first examination (RR = 1.50; P < 0.01). STP was not associated with clinical failure (P = 0.90). Thoracic ultrasound severity at diagnosis and calf age, but not early-life STP, provide valuable prognostic insight for short-term treatment success in pre-weaned dairy calves with BRD.