FieldDxHistophilus Septicemia of CattleClinical signs, differential diagnosis, treatment and prevention in cattle.
Overview
A bacterial cause of pneumonia and systemic disease in feedlot cattle, part of the bovine respiratory disease complex. Histophilus somni, which can spread from the lungs to the brain, heart, joints and pleural/pericardial surfaces.
Clinical signs
- Sudden death may be the first thing seen.
- Profound lethargy is the most noticeable sign.
- Fever and rapid breathing.
- Stiffness, muscle weakness, ataxia and lameness.
- Extreme dyspnoea in the pleuritic form.
- Severe exercise intolerance and collapse in the myocarditic form.
- Recumbency and hyperaesthesia in the encephalitic form.
- Blindness where the CNS is involved.
Predisposing factors
- Recently weaned calves held in confinement.
- High-stress transition into the feedlot.
- Concurrent bovine respiratory syncytial virus infection.
- Risk peaks 21-23 days after arrival at the feedlot.
Treatment
- Florfenicol 20 mg/kg IM into the neck only, repeated after 48 hours, or 40 mg/kg SC once.
- Antimicrobials work best given early.
- Prophylactic and metaphylactic antimicrobials have limited effect.
Drugs mentioned: Florfenicol
Prevention
1. Monovalent or multivalent bacterins containing H. somni. 2. A two-dose protocol works better than one. 3. First dose around 2 months old, booster at preweaning or feedlot arrival. 4. Efficacy varies because of biofilm formation and timing.
Source
MSD Veterinary Manual — Histophilosis (accessed 2026-07-31)
A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER — Histophilus Septicemia Of Cattle (Histophilus Somni Or Haemophilus Somnus Disease Complex)
Condensed and attributed, never reproduced whole. Open the full entry in the app.