Bacterial Pneumonia in Cattle with Bovine Respiratory Disease (BRD)

Introduction

Bacterial pneumonia is a common respiratory disease in cattle and is an important part of Bovine Respiratory Disease Complex (BRD). It mainly affects calves, feedlot cattle, and stressed animals after weaning, transportation, overcrowding, or viral infections. The disease causes inflammation and damage in the lungs, leading to breathing problems, poor growth, and sometimes death.

Main Bacterial Causes

The major bacteria involved in BRD include:

• Mannheimia haemolytica – the most common and severe bacterial cause of pneumonia in cattle.
• Pasteurella multocida – causes milder but important lung infections.
• Histophilus somni – can cause pneumonia along with heart, brain, and pleural infections.
• Mycoplasma bovis – commonly associated with chronic pneumonia, arthritis, and ear infections.
• Bibersteinia trehalosi – may cause sudden death and severe respiratory outbreaks.
• Trueperella pyogenes – often involved in chronic lung abscesses.

How Disease Develops

Under normal conditions, many of these bacteria live harmlessly in the upper respiratory tract of healthy cattle. Stress factors such as:

• weaning,
• transportation,
• overcrowding,
• poor ventilation,
• sudden weather changes,
• and viral infections

weaken the animal’s immune defenses. The bacteria then move into the lungs, multiply rapidly, and produce toxins that damage lung tissue, causing pneumonia.

Clinical Signs

Early signs of bacterial pneumonia include:

• Fever (40–41°C)
• Depression and weakness
• Loss of appetite
• Nasal discharge
• Moist cough
• Rapid and shallow breathing

As the disease becomes severe, cattle may show:

• difficult breathing,
• grunting,
• pleurisy,
• weight loss,
• chronic coughing,
• and poor body condition.

In chronic cases, lung abscesses may develop.

Postmortem Lesions

Different bacteria produce different lung lesions:

• Mannheimia haemolytica causes severe fibrinous and hemorrhagic bronchopneumonia with lung consolidation.
• Pasteurella multocida usually causes purulent bronchopneumonia with less tissue damage.
• Histophilus somni may cause pleuritis and septicemia affecting multiple organs.
• Mycoplasma bovis commonly causes caseonecrotic pneumonia along with arthritis and otitis.
• Chronic infections may result in pulmonary abscesses.

Diagnosis

Diagnosis is based on:

• clinical signs,
• necropsy findings,
• bacterial culture,
• PCR testing,
• immunohistochemistry,
• and samples collected from the lower respiratory tract such as deep nasopharyngeal swabs or bronchoalveolar lavage.

Samples should ideally be collected before antimicrobial treatment for accurate culture and sensitivity testing.

Treatment

Early treatment is very important for successful recovery. Broad-spectrum long-acting antimicrobials commonly used for BRD include:

• tulathromycin,
• gamithromycin,
• tilmicosin,
• florfenicol,
• and enrofloxacin.

NSAIDs may also help reduce fever and inflammation. In chronic cases with lung abscesses, treatment response is often poor, and culling may be considered.

Prevention and Control

Important control measures include:

• proper ventilation,
• reducing stress,
• minimizing mixing of animals,
• preconditioning before transport,
• good nutrition,
• vaccination against respiratory pathogens,
• and metaphylaxis in high-risk cattle.

Vaccines against Mannheimia haemolytica, Histophilus somni, and Mycoplasma bovis are available, although their effectiveness may vary.

Key Points

• Bacterial pneumonia is a major cause of economic loss in cattle production.
• Stress and viral infections play an important role in disease development.
• Mannheimia haemolytica is the most important bacterial pathogen in BRD.
• Early diagnosis and prompt antimicrobial treatment improve recovery.
• Good management and vaccination programs are essential for disease prevention.