Bovine Respiratory Disease (BRD) in Calves: Early Detection, Treatment, and Prevention That Actually Works

By Dr Duncan Houston

Bovine respiratory disease is one of the most common and costly health problems in cattle production. It affects growth, survival, fertility, and long-term performance. The challenge is that BRD rarely starts with obvious signs. It begins subtly, and by the time it is clearly visible, lung damage is often already present.

Most losses are not due to lack of treatment. They are due to delayed recognition.

This guide explains how BRD actually develops, how to detect it early using practical tools like DART scoring, how to treat it effectively, and how to reduce its impact across the herd.

Quick Answer

Bovine respiratory disease is a complex condition involving viral damage followed by bacterial infection. Early detection using systems like DART scoring is critical. Treatment should begin immediately with appropriate antibiotics and supportive care, while prevention focuses on vaccination, stress reduction, and environmental management. If calves show depression, reduced appetite, breathing changes, or fever, act quickly.

Why BRD Matters More Than Most Producers Realise

BRD is not just a respiratory issue. It is a performance issue.

Impacts include:

• Reduced weight gain

• Lower weaning weights

• Delayed finishing

• Reduced fertility in replacement heifers

• Increased treatment costs

• Higher mortality

Clinical Insight

The biggest cost is often not death. It is reduced lifetime performance in calves that survive but never fully recover.

What Actually Causes BRD

BRD is not caused by one pathogen. It is a combination of:

• Viral infection

• Bacterial infection

• Environmental stress

• Immune suppression

Common Viral Triggers

• Bovine respiratory syncytial virus (BRSV)

• Infectious bovine rhinotracheitis (BHV-1)

• Parainfluenza virus (PI3)

These viruses damage the respiratory tract and weaken defence mechanisms.

Common Bacterial Pathogens

• Mannheimia haemolytica

• Pasteurella multocida

• Histophilus somni

• Mycoplasma bovis

These bacteria take advantage of damaged lung tissue and cause pneumonia.

Clinical Insight

BRD is best understood as a cascade. Viral damage comes first, then bacteria take over. That is why timing matters so much in treatment.

The DART System: How to Detect BRD Early

Early detection is the most important factor in successful treatment.

DART Scoring

D – Depression

• Head down

• Droopy ears

• Reduced alertness

A – Appetite

• Reduced feeding

• Slower intake

• Separation from feed

R – Respiration

• Increased breathing rate

• Laboured breathing

• Coughing

T – Temperature

• Fever above 40°C (104°F)

Decision Checkpoint

You do not need all four signs. Even one or two changes, especially appetite and behaviour, should trigger closer inspection.

What Early BRD Actually Looks Like

Early cases are often subtle:

• Slight drop in feed intake

• Calf hanging back from the group

• Mild increase in respiratory effort

• Small temperature rise

Clinical Insight

The calves that look only “slightly off” are often the ones you need to act on fastest. Waiting for obvious respiratory distress is already too late.

Severity Framework: How Worried Should You Be?

Mild

• Slight behavioural change

• Normal appetite or slightly reduced

• No major respiratory signs

Monitor closely and reassess within 24 hours.

Moderate

• Reduced appetite

• Clear depression

• Mild respiratory signs

• Fever present

Needs prompt treatment.

High Risk

• Marked respiratory effort

• High fever

• Reduced intake

• Multiple calves affected

Immediate treatment required.

Critical

• Open-mouth breathing

• Severe distress

• Collapse

Emergency.

Diagnosis: What Confirms BRD

Veterinary assessment may include:

• Lung auscultation

• Temperature monitoring

• Ultrasound to assess lung damage

• Necropsy in early deaths

• Bacterial culture and sensitivity

Clinical Insight

Accurate diagnosis improves treatment success and helps avoid repeated treatment failure.

Treatment: What Actually Works

Immediate Treatment Is Critical

Treatment should begin as soon as BRD is suspected.

Core Treatment Approach

• Broad-spectrum antibiotics targeting key pathogens

• Anti-inflammatories to reduce lung inflammation and fever

• Supportive care including hydration and nutrition

Why Antibiotic Choice Matters

Initial treatment must cover:

• Mannheimia

• Pasteurella

• Histophilus

• Mycoplasma

Follow-up treatment should be guided by:

• Response

• Culture results where available

Decision Checkpoint

If there is no improvement within 48 to 72 hours, reassess treatment strategy.

Supportive Care: Often Overlooked

Supportive care improves recovery:

• Maintain hydration

• Ensure access to feed

• Reduce stress

• Improve environment

Clinical Insight

Calves that continue eating and drinking recover faster and maintain better growth.

Preventing BRD: What Actually Reduces Risk

Vaccination

Target:

• BRSV

• BHV-1

• PI3

• Key bacterial pathogens

Timing matters. Vaccination must occur before exposure.

Stress Reduction

Avoid:

• Abrupt weaning

• Sudden diet changes

• Overcrowding

• Mixing unfamiliar groups

Environment

Ensure:

• Good airflow

• Dry bedding

• Reduced dust

• Adequate space

Management

• Monitor calves daily

• Identify early signs

• Act quickly

Clinical Insight

Most BRD outbreaks are management problems, not just pathogen problems.

Chronic and Recurrent Cases

Some calves do not respond well to initial treatment.

These cases may:

• Have deeper lung damage

• Require different antibiotics

• Show ongoing poor performance

Decision Checkpoint

If a calf remains unwell after treatment, reassess early rather than repeating the same protocol.

Monitoring the Herd

Track:

• DART scores

• Treatment rates

• Response to treatment

• Mortality

• Growth performance

Patterns often reveal:

• Timing issues

• Environmental problems

• Vaccination gaps

What Should You Do Right Now?

If you suspect BRD:

1. Check temperature

2. Assess DART signs

3. Identify affected calves early

4. Start treatment immediately

5. Contact your veterinarian

6. Review environmental and management factors

Time-Based Guidance

• Early signs: act within hours

• Moderate cases: treat same day

• Severe cases: urgent intervention

Common Mistakes Producers Make

• Waiting too long to treat

• Ignoring early appetite changes

• Treating individuals without assessing the group

• Using incorrect antibiotics

• Failing to reassess non-responders

• Underestimating environmental factors

How to Reduce BRD Long-Term

• Use consistent vaccination programs

• Improve housing and airflow

• Reduce stress during transitions

• Train staff in early detection

• Monitor herd data regularly

Prevention is far more effective than repeated treatment.

FAQs

What is the earliest sign of BRD?

Reduced appetite and mild depression are often the first signs.

How quickly should treatment start?

Immediately once BRD is suspected.

Can calves recover fully?

Some do, but lung damage can reduce long-term performance.

Is vaccination enough to prevent BRD?

No. It reduces risk but must be combined with good management.

When should I call a vet?

At the first signs of disease, especially if multiple calves are affected.

Final Thoughts

BRD is one of the most important diseases to manage well in cattle production.

The key drivers of success are:

• early detection

• rapid treatment

• correct antibiotic use

• supportive care

• strong prevention systems

Most losses happen because action comes too late.

The earlier you act, the better the outcome.

If you want help refining BRD protocols, improving early detection, or reviewing treatment strategies, ASK A VET™ can help you act sooner and reduce long-term losses.