Bovine Respiratory Disease (BRD) is the disease group responsible for the highest morbidity and mortality in feedlot cattle. It is a multifactorial syndrome driven by the interaction of viral and bacterial pathogens, environmental stressors, and the immune status of the host. In newly received feeder cattle, the form commonly called shipping fever is the acute pneumonia complex triggered by transport and commingling stress. This article reviews BRD etiology, pathogenesis, early detection, treatment, and herd-level prevention.
Economic Impact
BRD is responsible for very large annual losses in feedlot production. Morbidity in receiving pens often ranges from 15-45%, while mortality commonly falls between 1-5%. Animals that experience BRD usually show lower ADG, poorer FCR, and reduced carcass value, and chronic cases greatly increase culling pressure.
1. BRD Etiology: The Disease Triangle
BRD does not arise from a single agent. It develops through the interaction of the host, the pathogen, and the environment. Stress weakens immune defenses, viral agents damage the respiratory epithelium, and bacterial pathogens establish secondary infection.
- BVDV: Immunosuppression; PI animals are continuous virus sources
- IBR (BHV-1): Necrosis in the upper respiratory tract
- BRSV: Lower respiratory disease and bronchiolitis
- PI3: Mild primary damage but strong synergy with other pathogens
- BCoV: Respiratory and enteric involvement
- Mannheimia haemolytica: Most common, fibrinous pneumonia, leukotoxin
- Pasteurella multocida: Bronchopneumonia, often milder than Mannheimia
- Histophilus somni: Septicemia, TME, myocarditis
- Mycoplasma bovis: Chronic pneumonia, arthritis, otitis
- Trueperella pyogenes: Chronic abscess-forming complications
- Transport stress: Long distance, thermal stress, feed and water deprivation
- Commingling: Mixing cattle from multiple sources
- Poor ventilation: Dust, ammonia, stagnant air
- Overcrowding: Higher pathogen pressure
- Dietary transition stress: Rumen disturbance and lower immune resilience
- Rapid weather shifts: Large day-night temperature differences
2. Pathogenesis: How Shipping Fever Develops
BRD Pathogenesis Cascade
Transport and commingling raise cortisol and weaken immunity
BVDV, IBR, BRSV damage the epithelium and reduce mucociliary clearance
Nasopharyngeal pathogens descend into the lower respiratory tract
Leukotoxins, fibrinous inflammation, and pulmonary consolidation develop
Pleuritis, abscessation, chronic lung damage, or death may follow
ADG declines, FCR worsens, treatment costs rise, and carcass quality drops
3. Clinical Signs and Early Detection
3.1 Clinical Presentation
| Stage | Main Findings | Rectal Temperature | General Prognosis |
|---|---|---|---|
| Early (1-2 days) | Mild depression, reduced appetite, serous nasal discharge, mild cough | 39.5-40.5°C | Good if treated promptly |
| Moderate (3-5 days) | Marked depression, mucopurulent discharge, frequent cough, labored breathing, ocular discharge | 40.5-41.5°C | Guarded but still favorable with timely therapy |
| Advanced (>5 days) | Severe dyspnea, open-mouth breathing, purulent discharge, edema, recumbency | >41.5°C or low in septic shock | Poor |
| Chronic | Chronic cough, poor thrift, poor hair coat, reduced performance | Normal or mildly elevated | May require culling or salvage decisions |
3.2 The DART Scoring System
Consistent daily observation is critical for early detection. The DART system evaluates Depression, Appetite, Respiration, and Temperature and provides a practical decision tool for receiving cattle.
DART Scoring
| Parameter | 0 (Normal) | 1 (Mild) | 2 (Moderate) | 3 (Severe) |
|---|---|---|---|---|
| Depression | Bright and active | Slightly dull | Clearly dull, head lowered | Recumbent or unable to rise normally |
| Appetite | Normal intake | Reduced | Very little intake | Feed refusal |
| Respiration | Normal | Mild increase, occasional cough | Clearly increased, abdominal effort | Marked dyspnea or open-mouth breathing |
| Temperature | <39.5°C | 39.5-40.0°C | 40.0-41.0°C | >41.0°C |
Total score ≥4: start treatment | Score ≥7: aggressive treatment plus isolation
4. Treatment Protocols
4.1 Antimicrobial Therapy
Antibiotic choice should reflect expected pathogen spectrum, tissue penetration, duration of activity, and ease of administration. Treatment should begin as early as possible because delay reduces the chance of recovery and increases the risk of chronic lung damage.
| Antibiotic | Dose and Route | Main Spectrum | Withdrawal | Practical Note |
|---|---|---|---|---|
| Tulathromycin | Single SC dose | M. haemolytica, P. multocida, H. somni, often Mycoplasma coverage | Observe label | Long-acting macrolide, also used in metaphylaxis |
| Florfenicol | IM repeated dosing or single high-dose SC formulation | Broad bacterial BRD coverage | Observe label | Good pulmonary penetration |
| Enrofloxacin | Single SC protocol where approved | Broad spectrum including difficult cases | Observe label | Stewardship considerations are important |
| Tildipirosin | Single SC dose | M. haemolytica, P. multocida, H. somni | Observe label | Modern macrolide option |
| Oxytetracycline | Repeated long-acting protocol | Broad spectrum | Observe label | Economical but not always the strongest option |
| Ceftiofur | Single or repeated labeled protocols | M. haemolytica, P. multocida, H. somni | Observe label | Often valuable in selected cases |
4.2 Supportive Therapy
Supportive Care Protocol
- NSAIDs: Useful for fever, pain control, and reduction of pulmonary inflammation
- Fluid support: Oral or IV fluids in dehydrated animals
- Isolation: Separate sick cattle to reduce pathogen spread and stress
- Comfort: Dry bedding, proper air quality, and easy access to water
- Nutrition: Good-quality forage and adequate water access, with ration management matched to appetite
4.3 Response to Therapy and Retreatment
Treatment Follow-Up Protocol
- 48-72 hours: Reassess after the first treatment
- Signs of improvement: Lower temperature, better appetite, improved respiration
- No response: Consider a different drug class rather than repeating the same approach
- Third treatment need: Strongly suggests chronic BRD risk
- Chronic BRD: Lung abscessation or pleuritis may make salvage or culling more appropriate
- Records: Keep precise treatment, dose, and response logs
5. Prevention Strategies
5.1 Vaccination Program
| Vaccine Group | Timing | Type | Main Note |
|---|---|---|---|
| IBR + PI3 + BVDV + BRSV | Ideally before arrival or at arrival depending on risk | Modified-live or inactivated | MLV can create faster immunity but requires careful use |
| Mannheimia + Pasteurella | Often at arrival | Bacterin or toxoid-based products | Leukotoxin-containing products may be advantageous |
| Histophilus somni | At arrival in high-risk systems | Bacterin | Useful where herd history supports it |
| Mycoplasma bovis | Case-dependent | Bacterin | Efficacy remains debated |
| Booster | Usually 2-4 weeks later when needed | — | Critical for primary immunity in many programs |
5.2 Metaphylaxis
Metaphylaxis means giving antimicrobial treatment to high-risk cattle on arrival before clinical signs appear. In truly high-risk groups, it can significantly reduce BRD morbidity and mortality. It should be reserved for populations with genuine risk rather than routine indiscriminate use.
When Metaphylaxis Is Reasonable
- High-risk groups: Mixed-source, long-transport, poorly documented vaccination history, light-weight calves
- Common protocols: Long-acting macrolides such as tulathromycin or tildipirosin at arrival
- Caution: Antimicrobial stewardship matters; use only when justified
- Alternative: In lower-risk cattle, vaccination plus strong management may be sufficient
5.3 Environmental and Management Strategies
- Air space: Adequate enclosed volume per animal
- Air exchange: Maintain fresh air without drafts
- Ammonia: Keep levels low
- Dust: Minimize during feed delivery and bedding handling
- Bedding: Keep dry and regularly renewed
- Stocking density: Avoid overcrowding in receiving pens
- Transport duration: Longer journeys increase risk sharply
- Loading density: Avoid excessive crowding in transport
- Arrival management: Immediate water and good hay access
- Rest period: 24-48 hours before aggressive nutritional transitions
- Source separation: Limit unnecessary commingling
- BVDV PI screening: Identify and remove PI animals where possible
6. BVDV and Persistent Infection (PI)
PI Animals: Silent Super-Spreaders
Calves infected in utero with BVDV may be born persistently infected (PI) and shed virus continuously throughout life. Even a single PI animal can destabilize a receiving group and trigger major BRD problems. Ear-notch antigen testing at arrival is a practical way to identify and remove these animals.
7. Long-Term Performance Effects of BRD
| Parameter | No BRD | One BRD Episode | Two or More Episodes |
|---|---|---|---|
| ADG | Reference | Lower | Substantially lower |
| FCR | Reference | Worse | Much worse |
| Carcass weight | Reference | Reduced | Further reduced |
| Carcass quality grade | Reference | Lower | Markedly lower |
| Removal from the herd | Low | Higher | Highest |
8. Herd-Level Monitoring
| Parameter | Target | Alarm Threshold | How to Monitor |
|---|---|---|---|
| Receiving-pen BRD morbidity | Keep low | Rising daily treatment need | Daily observation and DART scoring |
| BRD mortality | Very low | Upward drift in case fatality | Cumulative death records |
| First-treatment success | High | Poor response at recheck | Treatment records |
| Chronic BRD rate | Low | Frequent third-treatment animals | Flag repeated-treatment cattle |
| Case fatality rate | Low | Increasing deaths among treated animals | Deaths ÷ treated animals |
| Slaughter lung lesions | Low lesion prevalence | High lesion feedback from the plant | Abattoir feedback and lung scoring |
9. References
- Apley, M. (2006). Bovine respiratory disease: Pathogenesis, clinical signs, and treatment in lightweight calves. Veterinary Clinics of North America: Food Animal Practice, 22(2), 399-411.
- Cusack, P. M. V., et al. (2003). The medicine and epidemiology of bovine respiratory disease in feedlots. Australian Veterinary Journal, 81(8), 480-487.
- Griffin, D., et al. (2010). Bacterial pathogens of the bovine respiratory disease complex. Veterinary Clinics of North America: Food Animal Practice, 26(2), 381-394.
- Hessman, B. E., et al. (2009). Interaction between bovine viral diarrhea virus and bovine respiratory disease in feedlot cattle. The Bovine Practitioner, 43(2), 146-153.
- Nickell, J. S., & White, B. J. (2010). Metaphylactic antimicrobial therapy for bovine respiratory disease in stocker and feedlot cattle. Veterinary Clinics of North America: Food Animal Practice, 26(2), 285-301.
- Snowder, G. D., et al. (2006). Bovine respiratory disease in feedlot cattle: Environmental, genetic, and economic factors. Journal of Animal Science, 84(8), 1999-2008.