Mycoplasma ovipneumoniae in Sheep: Chronic Cough and Pneumonia

Mycoplasma ovipneumoniae, often shortened to M. ovi, is a bacterium that lives in the upper respiratory tract of sheep and goats. In some sheep it causes little obvious illness. In others, especially lambs or animals under stress, it can contribute to chronic coughing, reduced growth, and pneumonia.

This infection is tricky because it does not always act alone. Veterinary references describe M. ovi as an important predisposing organism that can damage normal airway defenses and make secondary infections with bacteria such as Mannheimia haemolytica or Pasteurella multocida more likely. That means a mild cough can sometimes turn into a more serious flock respiratory problem.

For pet parents and producers, the biggest challenge is that apparently healthy carriers can still spread the organism through respiratory secretions. A sheep that looks normal may still introduce infection into a new group. That is why your vet may focus not only on the sick sheep in front of you, but also on flock history, recent purchases, transport, weaning, and housing conditions.

M. ovi spreads mainly through close contact and respiratory droplets or secretions. Sheep can be infected by nose-to-nose contact, coughing, sneezing, and commingling during transport, shows, sales, breeding, or flock additions. USDA guidance also notes that some infected animals may appear healthy, which helps the organism move quietly through a group.

Disease severity often depends on more than the bacterium itself. Stress from weaning, crowding, poor ventilation, weather swings, transport, diet changes, and mixing unrelated sheep can weaken respiratory defenses. Merck Veterinary Manual also notes that M. ovipneumoniae can predispose sheep to secondary infection with Pasteurella and Mannheimia, which is one reason some cases stay mild while others become serious pneumonia.

In practical terms, many outbreaks are really a respiratory disease complex rather than a single-organism problem. Your vet may look for management triggers and co-infections at the same time, because controlling the environment is often as important as choosing medication.

Diagnosis starts with a good flock history and physical exam. Your vet will usually ask about age group affected, how long coughing has been present, whether new sheep were introduced, and whether there were recent stressors such as weaning, hauling, or weather changes. Temperature, breathing effort, lung sounds, body condition, and the number of affected sheep all help shape the next steps.

Because respiratory disease in sheep is often multifactorial, testing may include nasal or deep respiratory swabs for PCR, and in some cases bacterial culture and susceptibility testing if secondary pneumonia is suspected. Merck notes that culture and susceptibility testing are especially useful in outbreaks, valuable animals, or cases that are acute, chronic, or not responding as expected.

If a sheep dies or is euthanized, necropsy can be one of the most useful tools for the flock. Lung lesion patterns, tissue sampling, and histopathology can help separate M. ovi from other important causes of chronic respiratory disease. In flock situations, your vet may recommend testing more than one sheep, including both sick and apparently healthy contacts, to understand whether carrier animals are present.

Prevention starts with biosecurity. Quarantine new arrivals before mixing them into the flock, avoid unnecessary nose-to-nose contact with outside sheep or goats, and be cautious with animals returning from shows, sales, or breeding visits. Because healthy-looking carriers can shed M. ovi, your vet may recommend testing additions or chronic coughers before they join the main group.

Good air quality matters. Overcrowding, damp bedding, dust, and poor ventilation all increase respiratory stress. Lambs are especially vulnerable around weaning and other management changes, so keeping housing dry, reducing sudden stressors, and maintaining strong nutrition can lower the chance that a carrier state turns into active pneumonia.

If your flock has had repeated respiratory disease, prevention may need to be a flock plan rather than a one-time treatment. That can include separating age groups, limiting commingling, culling chronic poor-doers when appropriate, and reviewing outbreak patterns with your vet. There is no single prevention step that fits every farm, but steady biosecurity and management changes can meaningfully reduce disease pressure.