What is the current treatment protocol for bovine respiratory disease complex by pathogen and severity?

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Bovine respiratory disease complex (BRD) treatment is primarily antimicrobial, with drug selection driven by pathogen type and disease severity, since clinical signs alone cannot reliably distinguish the causative pathogen. 12 --- Pathogen-Directed Antimicrobial Selection For bacterial BRD caused by Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, antimicrobial therapy is the cornerstone of treatment. 27 In Canada, labeled options for dairy cows are limited to five antimicrobials: oxytetracycline, trimethoprim-sulfadoxine, ampicillin, penicillin, and ceftiofur. 1 Ceftiofur is the most commonly used antimicrobial, accounting for 75% of BRD cases treated in Québec dairy herds. 1 Ceftiofur hydrochloride (Excenel) is labeled for BRD at 0.5–1 mg CE/lb (1.1–2.2 mg CE/kg) IM or SC q24h for three consecutive days; Days 4 and 5 may be added for animals that do not show a satisfactory response after the initial three treatments. 14 For BRD only, an alternate every-other-day regimen of 1 mg CE/lb (2.2 mg CE/kg) IM or SC on Days 1 and 3 is also labeled. 14 Selection between the 0.5 and 1 mg CE/lb dose levels and between the daily and every-other-day regimens is based on disease severity, pathogen susceptibility, and clinical response. 14 No more than 15 mL should be injected per injection site. 14 For Mycoplasma bovis, standard beta-lactam and many conventional antimicrobials have limited efficacy due to the absence of a cell wall; florfenicol administered by nebulization has been evaluated as an alternative delivery route. 913 Florfenicol by inhalation shortens recovery time compared to subcutaneous administration alone, with clinical improvement observed by Day 2 in nebulization groups versus later in the subcutaneous group. 13 Calves with clinical respiratory scores of 12 or above died across all treatment groups regardless of route. 13 M. bovis was the primary bacterial pathogen and bovine respiratory syncytial virus (BRSV) the primary viral pathogen id