Bovine Respiratory Disease Complex

Bovine Respiratory Disease (BRD) complex, historically called 'shipping fever,' is the leading cause of morbidity and mortality in North American beef cattle. It is a multifactorial disease involving viral infection, bacterial superinfection, and environmental stressors.

Viral pathogens (primary insult):

• BHV-1 (Infectious Bovine Rhinotracheitis — IBR): Causes severe tracheitis, rhinitis; immunosuppressive; latency in trigeminal ganglion
• BVDV (Bovine Viral Diarrhea Virus): Immunosuppressive; persistent infection (PI) calves are reservoir; mucosal disease
• BRSV (Bovine Respiratory Syncytial Virus): Causes severe interstitial pneumonia; syncytia formation; young calves most susceptible
• PI3 (Parainfluenza-3): Mild respiratory disease; often subclinical; predisposes to bacterial infection

Bacterial pathogens (superinfection):

• Mannheimia haemolytica: Most common; serotype A1; produces leukotoxin (cytotoxic to macrophages and neutrophils); fibrinous pneumonia
• Pasteurella multocida: Less virulent; often secondary; capsule type A or D
• Histophilus somni: Causes thrombotic meningoencephalitis (TME), myocarditis, septicemia in addition to pneumonia
• Mycoplasma bovis: Chronic, antibiotic-resistant; polyarthritis, mastitis, otitis media may coexist

Risk factors: Weaning stress, transport (mixing, dehydration, fasting), commingling, castration/dehorning at arrival, inclement weather, poor ventilation, nutritional stress, vitamin/mineral deficiencies.

Clinical signs:

• Fever (40–41.5°C / 104–106.8°F)
• Depression, anorexia, decreased rumination
• Mucopurulent nasal discharge
• Cough (moist or dry)
• Tachypnea, dyspnea, open-mouth breathing
• Thoracic auscultation: Crackles, wheezes, decreased sounds in consolidated areas

Diagnostic approach:

• Clinical diagnosis: Based on history (recent shipping/weaning), signs, and auscultation findings
• Thoracic ultrasound: Consolidation, pleural effusion, lung abscessation; useful for severity assessment
• Necropsy: Cranioventral lung consolidation, fibrinous pleuropneumonia, interlobular edema; culture from fresh lung tissue

Laboratory:

• CBC: Leukocytosis or leukopenia (severe); fibrinogen ↑ (acute phase protein)
• Serology: Paired titers for viral pathogens; BVDV PI testing (ear notch IHC or PCR)
• Nasopharyngeal culture/PCR: Identify bacterial pathogens and antimicrobial sensitivity

Metaphylaxis (mass treatment on arrival):

• Indicated for high-risk groups (long transport, commingled, lightweight calves, inclement weather)
• Long-acting antibiotics: Tulathromycin (Draxxin), tilmicosin (Micotil), florfenicol (Nuflor), gamithromycin (Zactran), oxytetracycline
• Reduces morbidity and mortality in high-risk populations

Individual treatment:

• First-line (severity-dependent): Tulathromycin SC (long-acting, broad spectrum), florfenicol, ceftiofur
• NSAIDs: Flunixin meglumine (reduce fever, inflammation, endotoxemia, improve feed intake)
• Supportive: Fluid therapy, nutrition, isolation
• Re-treatment: ~30% may need second treatment; consider different antibiotic class

Vaccination:

• Core respiratory vaccines: IBR (MLV or killed), BVDV (MLV; must ensure no PI status), BRSV, PI3
• Timing: Pre-weaning booster, pre-shipping booster
• Bacterial vaccines: Mannheimia/Pasteurella (conditioned, not always effective); M. haemolytica leukotoxoid

Management:

• Low-stress weaning and handling
• Adequate bunk space and water access
• Proper ventilation (reduce ammonia, humidity, dust)
• Nutritional support (adequate trace minerals — copper, zinc, selenium; vitamin E)
• Arrival processing: Delay castration/dehorning 2–3 weeks; avoid combining multiple stressors