Mycoplasma synoviae (Infectious Synovitis) in Chickens

Quick Answer
  • Mycoplasma synoviae is a contagious bacterial infection of chickens that can affect the respiratory tract and joints, causing infectious synovitis.
  • Common signs include lameness, swollen hocks or footpads, reluctance to stand, sitting near feeders or drinkers, and sometimes a drop in egg production.
  • Infected birds can become lifelong carriers, so flock management and biosecurity matter as much as treatment.
  • Your vet may recommend flock testing with PCR or serology, and some cases also benefit from necropsy to confirm the diagnosis and rule out other diseases.
  • Cost range in the US is often about $75-$300 for an exam and basic flock guidance, $40-$100 per PCR sample, and roughly $58-$187+ for poultry necropsy depending on the lab and region.
Estimated cost: $75–$300

What Is Mycoplasma synoviae (Infectious Synovitis) in Chickens?

Mycoplasma synoviae is a contagious bacterial disease of chickens and other poultry. In some birds it causes a mild or even unnoticed respiratory infection. In others, especially when stress or other infections are involved, it can move into the joints and tendon sheaths and cause infectious synovitis. That is the form most pet parents notice, because birds may limp, sit more, or develop swollen hocks and footpads.

One frustrating part of this disease is that infected chickens can remain carriers for life. A bird may look improved after treatment, but still carry the organism and spread it to flockmates later. The infection can move through a flock by direct contact, respiratory secretions, contaminated shoes or equipment, and from hen to egg.

For backyard flocks, this means Mycoplasma synoviae is often both an individual-bird problem and a flock-health problem. If one chicken is lame or has swollen joints, your vet may want to think beyond that bird alone and consider testing, isolation, and long-term flock management.

Symptoms of Mycoplasma synoviae (Infectious Synovitis) in Chickens

  • Lameness or limping
  • Swollen hock joints
  • Swollen footpads
  • Reluctance to stand or tendency to sit
  • Depression or reduced activity
  • Pale or bluish comb, wattles, or head parts
  • Mild respiratory noise or rales
  • Drop in egg production or shell quality changes

Call your vet promptly if you notice swollen joints, limping, several birds acting stiff, or a sudden drop in laying. These signs are not specific to Mycoplasma synoviae, and other problems like bumblefoot, trauma, staphylococcal joint infection, viral disease, or nutritional issues can look similar.

See your vet immediately if a chicken cannot reach food or water, is breathing hard, has marked swelling, or multiple birds become sick over a short time. Fast flock spread raises concern for contagious disease and may change how your vet recommends isolation, testing, and biosecurity.

What Causes Mycoplasma synoviae (Infectious Synovitis) in Chickens?

The cause is infection with the bacterium Mycoplasma synoviae. This organism spreads in two main ways: vertically from an infected hen into eggs, and horizontally from bird to bird through close contact, respiratory secretions, and contaminated people, clothing, shoes, cages, feeders, or equipment.

Stress often makes disease more visible. A flock may carry the organism quietly for days to months, then start showing signs after transport, overcrowding, poor ventilation, temperature swings, laying stress, or another infection. That is one reason a bird can seem healthy when introduced and only later develop problems.

Backyard flocks are especially at risk when new birds are added without quarantine, birds of different ages are mixed, or visitors move between flocks without changing footwear and clothing. Once introduced, the organism can persist because recovered birds may remain carriers for life.

How Is Mycoplasma synoviae (Infectious Synovitis) in Chickens Diagnosed?

Diagnosis starts with your vet looking at the whole picture: flock history, new bird introductions, age groups, egg production changes, respiratory signs, and joint swelling. A physical exam can help identify which birds are most affected, but signs alone are not enough to confirm Mycoplasma synoviae.

Testing usually involves PCR, serology such as agglutination or ELISA, and sometimes culture. PCR is commonly used on respiratory samples or affected tissues because it can directly detect mycoplasma DNA. Serology can help with flock screening, especially when your vet is trying to understand whether exposure is widespread.

If a bird dies or is euthanized, necropsy can be very helpful. Joint and tendon sheath changes, along with lab testing, can support the diagnosis and help rule out other causes of lameness and swelling. Because several poultry diseases can overlap, your vet may also recommend additional testing for other respiratory or infectious conditions.

Treatment Options for Mycoplasma synoviae (Infectious Synovitis) in Chickens

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$75–$200
Best for: Mild cases, early flock concerns, or pet parents who need a practical first step while deciding on testing
  • Veterinary exam or teleconsult guidance where legally available
  • Isolation of visibly affected birds
  • Supportive care such as easy access to feed and water, cleaner bedding, and reduced perch height
  • Basic flock biosecurity review
  • Monitoring for spread, worsening lameness, or egg production changes
Expected outcome: Some birds improve clinically with supportive care, but the flock may still have carrier birds and recurrence is possible.
Consider: Lower upfront cost, but it does not confirm the diagnosis and may miss other contagious or painful conditions.
Most Common

Recommended Standard Treatment

$150–$450
Best for: Most backyard flocks with swollen joints, lameness, respiratory signs, or repeated disease in multiple birds
  • Veterinary exam and flock history review
  • PCR or serology for Mycoplasma synoviae
  • Targeted antimicrobial plan if your vet feels it is appropriate
  • Isolation and flock-management instructions
  • Discussion of egg production impact, carrier status, and whether to retain or cull affected birds
Expected outcome: Clinical signs often improve with appropriate management, but treatment may reduce signs more than it eliminates infection. Long-term carrier status remains a concern.
Consider: More informative and often more effective for symptom control, but costs more and may still not clear the organism from the flock.

Advanced / Critical Care

$300–$900
Best for: Complex outbreaks, valuable breeding flocks, recurrent disease, severe lameness, or pet parents wanting the clearest possible flock-level plan
  • Full diagnostic workup with PCR, serology, and necropsy of deceased birds when available
  • Testing for concurrent respiratory or flock diseases
  • Culture or additional lab work in complicated cases
  • Detailed flock eradication or depopulation-and-restart planning when appropriate
  • Intensive supportive care for severely lame or debilitated birds
Expected outcome: Best for understanding the true flock picture and reducing future spread, but outcomes depend on how widespread infection is and whether birds remain carriers.
Consider: Highest cost and more management effort, but gives the strongest information for long-term control and prevention decisions.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Mycoplasma synoviae (Infectious Synovitis) in Chickens

Bring these questions to your vet appointment to get the most out of your visit.

  1. Do my chicken's signs fit Mycoplasma synoviae, or are there other likely causes of joint swelling and lameness?
  2. Which birds in my flock should be isolated right now, and for how long?
  3. Would PCR, agglutination, ELISA, or necropsy give the most useful answer in my situation?
  4. If one bird tests positive, should I assume the whole flock has been exposed?
  5. What treatment options are reasonable for symptom control, and what are the tradeoffs of each?
  6. Are recovered birds likely to remain carriers and continue spreading infection?
  7. How should I clean boots, feeders, waterers, and equipment to lower flock spread?
  8. Should I avoid hatching eggs, selling birds, or bringing in new chickens until we know more?

How to Prevent Mycoplasma synoviae (Infectious Synovitis) in Chickens

Prevention starts with closed-flock thinking. The safest approach is to buy chicks or started birds from sources with strong health programs and, when possible, Mycoplasma-monitored breeding stock. In the US, National Poultry Improvement Plan programs help reduce Mycoplasma synoviae in breeder flocks, but backyard birds can still be exposed through swaps, auctions, informal sales, and contact with other flocks.

Quarantine all new birds before they join your flock. Keep separate shoes, tools, and carriers for your chickens when possible, and wash or disinfect equipment that moves between groups. Limit visitors who also keep poultry, and avoid sharing feeders, waterers, crates, or incubators unless they have been thoroughly cleaned.

Good daily management also matters. Reduce crowding, improve ventilation, keep bedding dry, and place food and water where they stay cleaner and are less attractive to rodents. Stress and poor housing can make a quiet infection flare into obvious disease.

There is not a routine backyard chicken vaccine option to rely on here, so prevention depends heavily on sourcing, quarantine, and biosecurity. If your flock has had repeated lameness, swollen joints, or unexplained production drops, ask your vet whether flock testing would help guide a longer-term prevention plan.

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