Bacterial Bronchopneumonia in Sheep: Pasteurella, Mannheimia and More

Bacterial bronchopneumonia is a lung infection that affects the small airways and nearby lung tissue. In sheep, the bacteria most often involved are Mannheimia haemolytica and Pasteurella multocida. Bibersteinia trehalosi can also play a role, especially in lambs. These organisms may live in the upper airway without causing trouble until stress, crowding, transport, weaning, weather swings, or another respiratory infection weakens normal defenses.

The disease often settles in the front and lower parts of the lungs. Some sheep show a gradual cough and reduced appetite. Others become sick very quickly with fever, fast breathing, profound depression, and even sudden death. Lambs and recently weaned young stock are at highest risk, especially if colostrum intake was poor or immunity is fading.

For pet parents and flock managers, the key point is that this is not a "wait and see" problem. Sheep tend to hide illness until they are quite sick. Prompt veterinary attention gives your flock the best chance for recovery and helps limit losses from death, poor growth, and chronic lung damage.

The main bacteria linked to bronchopneumonia in sheep are Mannheimia haemolytica and Pasteurella multocida. Bibersteinia trehalosi may also be involved. These bacteria are often considered opportunists. In other words, they commonly cause disease after the airway has already been stressed or damaged.

Common triggers include weaning, transport, commingling with unfamiliar animals, sudden diet change, overcrowding, poor ventilation, dust, damp bedding, and abrupt weather changes. Inadequate colostrum intake in young lambs can also increase risk. Respiratory viruses and Mycoplasma ovipneumoniae may set the stage for secondary bacterial infection by impairing the lung's normal defenses.

Not every sheep exposed to these bacteria gets sick. Disease tends to happen when the balance tips in favor of the pathogen. That is why management matters so much. Reducing stress, improving airflow, and isolating sick animals can be just as important as medication in controlling an outbreak.

Your vet will start with a flock history and physical exam. Important clues include recent weaning, transport, weather stress, crowding, poor growth, or sudden deaths. On exam, your vet may find fever, dehydration, increased breathing effort, and reduced rumen activity. Lung sounds can be abnormal, but in some sheep the chest may sound less dramatic than the illness really is.

Diagnosis is often based on the combination of history, clinical signs, and response to early treatment. Depending on the case, your vet may also recommend bloodwork such as a CBC and fibrinogen, ultrasound or radiographs, and airway sampling such as a transtracheal wash for cytology and culture. These tests can help confirm pneumonia, identify the bacteria involved, and guide antibiotic selection.

In flock outbreaks or deaths, necropsy can be very helpful. Typical lesions often involve the cranioventral lungs, with consolidation and sometimes fibrinous pleuropneumonia. Your vet may also want to rule out other causes of respiratory disease in sheep, including Mycoplasma infection, parasitic pneumonia, aspiration, ovine pulmonary adenocarcinoma, and important reportable diseases when signs or losses are unusual.

Prevention focuses on stress reduction and strong basic husbandry. Good ventilation is one of the biggest protective factors. Barns should have fresh air without heavy drafts at animal level. Keep bedding dry, reduce dust, avoid overcrowding, and provide enough bunk and water space so timid sheep are not pushed back. During weaning, transport, or regrouping, try to limit multiple stressors happening at once.

Lamb management matters too. Adequate colostrum intake supports early immunity, and careful nutrition helps young animals handle weaning better. Quarantine new arrivals, watch closely for cough or fever after commingling, and separate sick sheep promptly. In outbreak settings, your vet may recommend reviewing parasite control, mineral status, and other diseases that can weaken the flock.

Vaccination planning can be confusing because product availability and label use vary by region and species. In the United States, Merck notes there are no commercially available vaccines specifically for small ruminant pasteurellosis. That makes management even more important. Your vet can help you build a flock-specific prevention plan based on housing, season, lamb flow, and past pneumonia losses.