Mycoplasma gallisepticum Infection in Chickens: Chronic Respiratory Disease Guide
- Mycoplasma gallisepticum (MG) is a contagious bacterial infection that commonly causes chronic respiratory disease in chickens.
- Typical signs include sneezing, coughing, nasal discharge, bubbly or swollen eyes, noisy breathing, and a drop in egg production.
- Birds can become lifelong carriers even after treatment, so antibiotics may reduce signs but usually do not clear the infection from the flock.
- Stress, crowding, poor ventilation, cold weather, and other infections can make signs worse and speed spread through the flock.
- Your vet may recommend PCR testing, flock screening, isolation, supportive care, and a flock-level management plan.
What Is Mycoplasma gallisepticum Infection in Chickens?
Mycoplasma gallisepticum, often shortened to MG, is a contagious bacterial disease of poultry. In chickens, it is best known for causing chronic respiratory disease, a long-lasting upper respiratory infection that can flare during stress. Many birds show mild signs at first, but the infection can spread widely through a flock.
MG mainly affects the eyes, sinuses, nasal passages, and trachea. Chickens may sneeze, cough, breathe noisily, or develop watery, foamy, or swollen eyes. In laying hens, pet parents may also notice fewer eggs over time. Some birds look only mildly sick, while others become weak if secondary infections join in.
One of the hardest parts of MG is that infected chickens often remain carriers for life. That means a bird may improve clinically but still harbor the organism and spread it later, especially during stress such as weather changes, molting, transport, overcrowding, or adding new birds.
Because several serious poultry diseases can look similar at first, respiratory signs in chickens should not be guessed at home. Your vet can help sort out whether MG is most likely, whether testing is needed, and how to protect the rest of your flock.
Symptoms of Mycoplasma gallisepticum Infection in Chickens
- Sneezing or snicking
- Coughing or tracheal rattles
- Nasal discharge
- Watery, foamy, or bubbly eyes
- Conjunctivitis or swelling around the eyes
- Noisy or difficult breathing
- Reduced appetite, slower growth, or weight loss
- Drop in egg production
- Open-mouth breathing, marked lethargy, or sudden worsening from secondary infection
Mild MG cases may start with occasional sneezing, watery eyes, or a subtle breathing noise. More concerning cases can progress to swollen eyelids, thick discharge, poor appetite, weight loss, and obvious respiratory effort. In flock outbreaks, many birds may become affected even if only a few look seriously ill.
See your vet promptly if your chicken has labored breathing, open-mouth breathing, blue discoloration, severe eye swelling, weakness, or a fast drop in egg production across the flock. Because avian influenza, infectious laryngotracheitis, infectious bronchitis, and other contagious diseases can look similar, any significant respiratory outbreak deserves veterinary guidance and flock biosecurity right away.
What Causes Mycoplasma gallisepticum Infection in Chickens?
MG is caused by the bacterium Mycoplasma gallisepticum. It spreads in two main ways: horizontal transmission between birds and vertical transmission from infected breeder hens through eggs. In backyard flocks, the most common route is bird-to-bird spread through respiratory secretions, close contact, and contaminated hands, shoes, crates, feeders, or other equipment.
New birds are a major risk. A chicken can look healthy and still carry MG, then begin shedding more organisms after transport, weather stress, molting, crowding, or another illness. Once MG enters a flock, it can move quickly, especially where ventilation is poor or birds are housed closely together.
MG often becomes more serious when other problems are present. Poor air quality, ammonia buildup, dust, cold stress, and concurrent infections can all worsen signs. Secondary bacteria such as E. coli may turn a mild respiratory problem into a much more serious flock event.
Wild birds and mixed-source poultry can also complicate disease control. That is why your vet may focus not only on the sick bird, but also on flock history, recent additions, hatchery source, housing, and daily biosecurity habits.
How Is Mycoplasma gallisepticum Infection in Chickens Diagnosed?
Diagnosis starts with a flock history and physical exam. Your vet will ask about new birds, recent swaps or shows, egg production changes, age groups in the flock, ventilation, and how many birds are affected. Respiratory signs alone are not enough to confirm MG because several poultry diseases can look similar.
Testing is often needed. Real-time PCR on choanal, tracheal, or other respiratory samples is commonly used to detect MG. Depending on the situation, your vet may also recommend flock screening with agglutination or ELISA serology, culture, or necropsy of a recently deceased bird. In some cases, a broader respiratory panel is helpful to look for coinfections.
Differentials matter. Your vet may want to rule out infectious bronchitis, infectious laryngotracheitis, Newcastle disease, avian influenza, infectious coryza, gapeworm, environmental irritation, or secondary bacterial disease. This is especially important if birds are severely ill, deaths are occurring, or the outbreak is moving quickly.
For backyard flocks, diagnosis is often about building a practical plan, not only naming the organism. Your vet can help decide whether to test one bird, several birds, or the whole flock, and whether the best next step is treatment, long-term management, quarantine, or depopulation and restocking after cleanup in severe situations.
Treatment Options for Mycoplasma gallisepticum Infection in Chickens
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Office or farm-call exam focused on the sickest bird or small group
- Isolation of visibly affected birds
- Supportive care plan for warmth, hydration, easier access to feed and water, and improved coop ventilation
- Basic flock biosecurity guidance and quarantine recommendations
- Empiric medication discussion with your vet when MG is strongly suspected, understanding this may reduce signs but not clear carrier status
Recommended Standard Treatment
- Veterinary exam plus targeted flock history and housing review
- PCR testing on respiratory swabs and/or serology for flock screening
- Medication plan selected by your vet based on flock goals, egg use, withdrawal considerations, and likely coinfections
- Supportive care, isolation, and environmental correction such as lowering dust and ammonia
- Clear guidance on quarantine, monitoring exposed birds, and whether to pause showing, selling, or adding birds
Advanced / Critical Care
- Expanded diagnostics such as respiratory panels, culture, necropsy, or multiple-bird testing
- Treatment of severe secondary infections or complicated airsac disease under your vet's direction
- Hospitalization or intensive supportive care for high-value birds when available
- Flock-level consultation on long-term containment, culling decisions, depopulation/restocking, and sourcing MG-monitored replacement birds
- Coordination with diagnostic labs or state poultry health resources when a reportable or high-concern disease must be ruled out
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Mycoplasma gallisepticum Infection in Chickens
Bring these questions to your vet appointment to get the most out of your visit.
- Does this look most consistent with MG, or do we need to rule out avian influenza, infectious bronchitis, ILT, or another respiratory disease?
- Which birds should we test first, and would PCR, serology, or necropsy give the most useful answer for my flock?
- If we treat, what is the goal—symptom control, lowering spread, protecting egg production, or helping the sickest birds recover?
- Will treated birds still be carriers, and how should that affect future flock additions, hatching eggs, or sales?
- What medication withdrawal times or egg-use restrictions should I follow for any treatment you prescribe?
- Should I isolate sick birds, or is this already a whole-flock management issue?
- What coop changes would help most right now—ventilation, dust control, stocking density, or cleaning routines?
- When would you recommend culling, depopulation, or restocking from NPIP-monitored sources instead of ongoing management?
How to Prevent Mycoplasma gallisepticum Infection in Chickens
Prevention starts with closed-flock thinking whenever possible. The safest approach is to avoid bringing in birds from swaps, auctions, mixed backyard sources, or flocks with unknown health status. If you do add birds, quarantine them for at least 30 days, watch closely for respiratory signs, and handle your resident flock before the newcomers.
Source matters. Buying chicks or hatching eggs from breeders participating in NPIP or other monitored health programs can reduce risk, though no system removes every possibility. Ask about flock health history, testing, and whether the source monitors for Mycoplasma gallisepticum.
Daily biosecurity also matters more than many pet parents realize. Clean and disinfect shared equipment, limit visitors in the coop area, change footwear, wash hands, control rodents, and reduce contact with wild birds. Good ventilation, lower dust, and avoiding overcrowding can also reduce respiratory stress that makes outbreaks worse.
If MG has already been identified in your flock, prevention shifts to containment. Work with your vet on isolation, flock movement decisions, breeding plans, and whether long-term management or flock replacement makes the most sense. Because recovered birds may remain carriers, preventing spread to new birds is often the most important goal.