Mycoplasma hyosynoviae Infection in Pigs: Lameness, Swollen Joints, and Pain
- Mycoplasma hyosynoviae is a bacterial infection that commonly causes acute arthritis and lameness in growing, finishing, and young adult pigs, especially after about 10 weeks of age.
- Affected pigs are often painful but not feverish. Common signs include reluctance to rise, stiff gait, shifting-leg lameness, swollen major joints, and a 'dog-sitting' posture.
- See your vet promptly if a pig will not bear weight, has multiple swollen joints, stops eating, or several pigs become lame in a short time.
- Diagnosis usually combines exam findings with joint fluid or joint swab PCR testing. Oral fluids or tonsil samples may support herd-level investigation, but joint samples are most useful for a sick pig.
- Typical US cost range for exam, sample collection, and lab testing is about $150-$500 per pig, with herd workups and multiple PCR panels often costing more.
What Is Mycoplasma hyosynoviae Infection in Pigs?
Mycoplasma hyosynoviae is a cell-wall-free bacterium that commonly lives in the upper respiratory tract and tonsils of pigs without causing obvious illness. In some pigs, it spreads from those tissues into the joints and triggers infectious arthritis, leading to pain, swelling, and sudden lameness. This pattern is well recognized in commercial swine herds and is considered endemic in many populations.
The disease is seen most often in grower, finisher, and young breeding pigs, typically from about 10 to 24 weeks of age, although older pigs can also be affected. Clinical signs often appear quickly. A pig that looked normal yesterday may be stiff, reluctant to stand, or lame in one or more legs today.
Many pigs recover over time, but that does not mean the condition should be ignored. Pain can be significant, mobility can drop fast, and other causes of lameness such as trauma, erysipelas, Streptococcus, or osteochondrosis can look similar. Your vet can help sort out which problem is most likely and what level of care fits the pig, the herd, and your goals.
Symptoms of Mycoplasma hyosynoviae Infection in Pigs
- Sudden lameness in one or more legs
- Pain when walking, turning, or rising
- Soft swelling of major joints such as elbows, stifles, or hocks
- Stiff gait or shortened stride
- Reluctance to stand or move
- Shifting-leg lameness or multiple limbs affected
- Dog-sitting posture to reduce joint pressure
- Rough hair coat or poor thrift during the episode
- Reduced feed intake because movement is painful
- Usually little to no fever despite obvious joint pain
When to worry: contact your vet promptly if a pig is non-weight-bearing, has marked joint swelling, refuses feed or water, or if several pigs become lame within days. Mycoplasma hyosynoviae often causes low mortality, but pain and welfare concerns can be substantial. Severe lameness can also look like fractures, septic arthritis from other bacteria, erysipelas, or neurologic disease, so a hands-on exam matters.
What Causes Mycoplasma hyosynoviae Infection in Pigs?
This condition is caused by Mycoplasma hyosynoviae, a bacterium spread mainly through direct oro-nasal contact between pigs. Many pigs carry the organism in the tonsils or upper airway without looking sick. That carrier state is one reason outbreaks can seem to appear suddenly in a group that looked healthy before.
Disease develops when the organism moves from the respiratory tract into the bloodstream and then into the joints. Once there, it causes synovitis and arthritis, which leads to pain, joint fluid buildup, and lameness. The exact reason some pigs become clinically affected while others remain carriers is not fully understood.
Several factors appear to increase risk, including stress, mixing groups, transport, handling, and joint trauma or underlying osteochondrosis. In herd settings, concurrent health challenges may also make lameness outbreaks more noticeable. Because other infectious and noninfectious causes of lameness are common in pigs, your vet may recommend testing rather than assuming Mycoplasma is the only explanation.
How Is Mycoplasma hyosynoviae Infection in Pigs Diagnosed?
Diagnosis starts with a history and physical exam. Your vet will look at the pig's age, how quickly the lameness started, whether one or several joints are involved, and whether there is fever, skin change, trauma, or signs of another systemic illness. Mycoplasma hyosynoviae is often suspected when an older nursery or grow-finish pig has acute, painful joint swelling with little or no fever.
A presumptive diagnosis can be made from the pattern of signs and lesions, but definitive diagnosis requires identifying the organism. The most useful samples are usually joint fluid or a joint swab, ideally from pigs that have been clinically affected for about 3 to 4 days. PCR is commonly used because culture can be difficult and other mycoplasmas may overgrow the sample.
Depending on the situation, your vet may also suggest oral fluid, tonsil, or lung samples for herd-level investigation, plus testing for other causes of lameness. In some cases, necropsy and synovial tissue evaluation help confirm the diagnosis and rule out competing problems. Serology may be available, but it is less helpful for a single sick pig because many pigs are exposed without becoming clinically ill.
Treatment Options for Mycoplasma hyosynoviae Infection in Pigs
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Prompt isolation or hospital-pen setup with dry, non-slip bedding
- Hands-on veterinary exam or herd-guided treatment plan when available
- Empiric antimicrobial selected by your vet for likely mycoplasma arthritis
- Pain control or anti-inflammatory support if appropriate for the pig and intended use
- Reduced handling, easier access to feed and water, and close mobility monitoring
Recommended Standard Treatment
- Veterinary exam with lameness assessment and differential diagnosis
- Joint tap or joint swab collection for PCR, often plus additional bacterial testing as needed
- Targeted antimicrobial plan based on likely mycoplasma susceptibility and herd history
- Pain management, nursing care, and pen modifications to reduce slipping and joint stress
- Short-term follow-up to assess response and decide whether more pigs need evaluation
Advanced / Critical Care
- Full herd or group outbreak investigation with multiple PCR samples and broader infectious disease testing
- Necropsy of fresh untreated cases when available to confirm lesions and competing diagnoses
- Radiographs or advanced workup for severe, nonresponsive, or valuable breeding animals
- Intensive supportive care for non-ambulatory pigs, including repeated reassessment and welfare-based decision making
- Veterinary consultation on flow, mixing, ventilation, trauma reduction, and possible autogenous vaccine planning where appropriate
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Mycoplasma hyosynoviae Infection in Pigs
Bring these questions to your vet appointment to get the most out of your visit.
- Does this pig's age and pattern of lameness fit Mycoplasma hyosynoviae, or are trauma and other infections more likely?
- Which joint should we sample, and would a joint swab or joint fluid PCR give the best chance of an answer?
- Should we test only this pig, or do you recommend herd-level samples such as oral fluids or tonsil samples too?
- What treatment options fit this pig's condition and our goals for comfort, recovery, and herd management?
- Which pain-control and nursing steps are safe and practical for this pig?
- If this is Mycoplasma hyosynoviae, what signs would mean the pig is not responding as expected?
- What management changes could reduce stress, slipping, and joint trauma in the rest of the group?
- Are there withdrawal-time, food-animal, or record-keeping issues we need to follow with any medication you prescribe?
How to Prevent Mycoplasma hyosynoviae Infection in Pigs
Prevention focuses on reducing exposure, stress, and joint injury rather than relying on one perfect tool. Because many pigs can carry Mycoplasma hyosynoviae without obvious illness, biosecurity and flow matter. Avoid unnecessary mixing, quarantine incoming pigs when possible, and work with your vet on a herd plan if lameness has been recurring.
Good housing also helps. Provide clean, dry, well-ventilated pens with secure footing and enough space to move without repeated slipping or piling. Gentle handling is important, especially during sorting, loading, and treatment, because trauma to joints may increase the chance that a carrier pig becomes clinically lame.
There is no widely effective commercial vaccine for this disease, although autogenous vaccines may be considered in some herd situations under veterinary guidance. If your farm has repeated outbreaks, your vet may recommend a broader review of stocking density, transport stress, co-infections, and sample-based monitoring. Prevention is usually most successful when management changes and veterinary oversight are combined.