Mycoplasma hyosynoviae in Pigs: A Common Cause of Arthritis and Lameness
- Mycoplasma hyosynoviae is a bacterial cause of infectious arthritis that most often affects growing and finishing pigs, especially around 10-30 weeks of age.
- Affected pigs are often suddenly lame, usually in the hind limbs, and may have painful, swollen joints but little or no fever.
- Stress, mixing groups, transport, overcrowding, and waning maternal immunity can increase the chance of clinical disease in a herd.
- Diagnosis usually involves a herd history, physical exam, and PCR testing on joint fluid, joint swabs, tonsil, lung, or oral fluid samples through a veterinary diagnostic lab.
- Early veterinary care matters because many pigs improve with prompt treatment and supportive management, while delayed care can mean more pain, weight loss, and poorer performance.
What Is Mycoplasma hyosynoviae in Pigs?
Mycoplasma hyosynoviae is a bacteria that can cause infectious arthritis and lameness in pigs. It is considered common in many swine herds, but not every exposed pig becomes obviously sick. Clinical disease is seen most often in growing and finishing pigs, especially after maternal immunity fades.
This infection tends to target the joints rather than causing a dramatic whole-body illness. Many pigs develop sudden pain, stiffness, and reluctance to walk, often in the hind limbs. Soft swelling around larger joints such as the hocks, stifles, or elbows may be present. Mortality is usually low, but the condition can still have a major welfare and production impact because lame pigs eat less, move less, and may fall behind.
For pet pigs and small hobby herds, the same pattern can happen. A pig that was active a few days ago may suddenly seem sore, slow to rise, or unwilling to bear weight. Because several other conditions can also cause lameness, your vet will need to sort out whether this is Mycoplasma hyosynoviae, another infection, hoof or limb injury, erysipelas, or a noninfectious joint problem.
Symptoms of Mycoplasma hyosynoviae in Pigs
- Sudden lameness, often affecting one or more hind limbs
- Reluctance to stand, walk, or keep up with the group
- Stiff gait or short, painful steps
- Pain when joints are flexed or touched
- Soft, fluctuant swelling around major joints such as hocks, stifles, or elbows
- Shifting-leg lameness or intermittent improvement followed by recurrence
- Reduced feed intake and slower weight gain
- Usually little or no fever, especially compared with some other infectious causes of lameness
- Lying down more than usual or isolating from pen mates
- Stress-related flare-ups after transport, mixing, or other management changes
Mild cases may look like stiffness or a pig that is slower to rise. More concerning cases involve obvious pain, refusal to bear weight, repeated falling, or multiple pigs becoming lame over a short period. Because pigs with Mycoplasma hyosynoviae are often not markedly febrile, the problem can be missed early.
See your vet promptly if your pig cannot stand, has severe joint swelling, stops eating, develops fever, or if several pigs in the group become lame at once. Those signs can overlap with other urgent conditions, including erysipelas, trauma, septic arthritis from other bacteria, or neurologic disease.
What Causes Mycoplasma hyosynoviae in Pigs?
The cause is infection with Mycoplasma hyosynoviae, a bacteria commonly carried in swine populations. Sows and older pigs can serve as sources of infection, and piglets may carry the organism before showing any signs. As maternal immunity wanes, usually around 6-10 weeks of age, more pigs become susceptible and shedding may increase.
Clinical disease often appears later, most commonly in pigs 10-30 weeks old. Not every exposed pig becomes lame. Outbreaks are more likely when pigs are stressed by mixing groups, transport, overcrowding, abrupt feed or management changes, or challenging housing conditions such as drafts or temperature stress.
Joint disease may also be worsened by trauma or underlying wear-and-tear changes. In other words, the bacteria may be present in the herd, but stress and joint strain can help turn a silent infection into obvious arthritis. That is why your vet will usually look at both the pig and the management picture, not only the lab result.
How Is Mycoplasma hyosynoviae in Pigs Diagnosed?
Diagnosis starts with the signalment and pattern. Your vet will consider the pig's age, how suddenly the lameness started, whether one or several pigs are affected, and whether there is joint swelling without major fever or respiratory signs. That pattern can strongly suggest Mycoplasma hyosynoviae, but it does not confirm it.
To investigate further, your vet may collect joint fluid or joint swabs for PCR testing. Some diagnostic labs also accept tonsil, lung, or oral fluid samples for Mycoplasma hyosynoviae PCR. Iowa State University's Veterinary Diagnostic Laboratory lists a porcine PCR for this organism at about $25 per sample as of March 2026, which helps explain why herd-level testing plans can vary depending on how many samples are needed.
Your vet may also recommend testing to rule out other causes of lameness, especially erysipelas, Mycoplasma hyorhinis, Glaesserella parasuis, Streptococcus suis, trauma, hoof problems, and metabolic bone disease. In some cases, response to treatment helps support the diagnosis, but treatment response alone should not replace a proper workup when the picture is unclear.
Treatment Options for Mycoplasma hyosynoviae in Pigs
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm call or basic veterinary exam
- Focused lameness assessment of the affected pig or a few pigs
- Empiric herd-appropriate antimicrobial plan chosen by your vet when clinical signs strongly fit Mycoplasma hyosynoviae
- Pain control or anti-inflammatory support if appropriate and legal for the setting
- Rest, easier access to feed and water, improved footing, and reduced competition
- Basic isolation or reduced mixing to limit stress on affected pigs
Recommended Standard Treatment
- Veterinary exam plus herd history review
- PCR testing on joint fluid, joint swab, oral fluid, tonsil, or other appropriate samples
- Targeted antimicrobial treatment selected by your vet based on likely pathogens, label restrictions, and withdrawal considerations
- Supportive care plan for lame pigs, including pen modifications and monitoring of feed intake and mobility
- Review of stressors such as recent mixing, transport, stocking density, ventilation, and temperature swings
- Short-term follow-up to assess treatment response and whether more pigs are becoming affected
Advanced / Critical Care
- Expanded diagnostic workup with multiple PCR samples and broader differential testing
- Necropsy and laboratory evaluation of severely affected or deceased pigs when herd diagnosis is uncertain
- Detailed herd investigation with biosecurity, pig flow, and environmental review
- Intensive nursing care for nonambulatory pigs when appropriate
- Escalated treatment and monitoring plan directed by your vet for complicated, recurrent, or multi-pathogen outbreaks
- Consultation with a swine-focused veterinarian or diagnostic laboratory for herd-level control planning
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Mycoplasma hyosynoviae in Pigs
Bring these questions to your vet appointment to get the most out of your visit.
- Does my pig's age and pattern of lameness fit Mycoplasma hyosynoviae, or are other causes more likely?
- Which samples would give us the best chance of confirming the diagnosis in this pig or herd?
- Do you recommend PCR testing now, or is it reasonable to start treatment first based on the clinical picture?
- What other diseases do we need to rule out, especially erysipelas or other bacterial joint infections?
- Which medication options are appropriate here, and what withdrawal times or legal-use limits should I know about?
- What changes to housing, footing, stocking density, or group mixing could reduce stress and help recovery?
- If more pigs become lame, at what point should we shift from individual treatment to a herd-level plan?
- What prevention steps make the most sense for my setup over the next few weeks and months?
How to Prevent Mycoplasma hyosynoviae in Pigs
Prevention focuses on biosecurity, pig flow, and stress reduction. Because Mycoplasma hyosynoviae is commonly endemic in swine herds, the goal is often not perfect elimination but lowering the chance that pigs develop clinical arthritis. Your vet may recommend limiting commingling of pigs from different sources, tightening entry biosecurity, and reducing lateral introduction from older pigs or contaminated people, tools, and equipment.
Management matters a great deal. Try to avoid overcrowding, abrupt ration changes, rough handling, and unnecessary regrouping. Good footing, dry bedding or flooring, and stable environmental conditions can help reduce both stress and joint trauma. These steps are especially important during the age window when maternal immunity is fading and pigs are becoming more susceptible.
If lameness has already appeared in your herd, prevention also means early recognition and fast response. Promptly separating obviously lame pigs, documenting which age groups are affected, and working with your vet on targeted testing can keep a small problem from becoming a larger outbreak. There is no single prevention plan that fits every herd, so the most effective approach is one tailored to your pig flow, housing, and risk factors.