Mycoplasma in Chickens — What It Is, How It Spreads, and What Every Flock Owner Should Know
By Happy Heart Farms | Live Oak, Florida
Of all the health challenges backyard flock owners encounter, mycoplasma infections are among the most misunderstood — and among the most common. The word itself sounds intimidating, but mycoplasma is something millions of backyard chicken keepers deal with every year. Understanding what it is, how it behaves, and what you can realistically do about it will help you make better decisions for your flock and reduce a lot of unnecessary anxiety.
What Is Mycoplasma?
Mycoplasma is a genus of bacteria — but unlike most bacteria, mycoplasma organisms lack a cell wall entirely. This is what makes them unusual and, from a treatment standpoint, tricky: most antibiotics work by attacking bacterial cell walls, which means the classes of antibiotics that work against most common infections have no effect on mycoplasma at all.
Two species are primarily responsible for disease in backyard chickens: Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS). MG is far more commonly discussed because it causes the most visible and impactful symptoms, but MS is widespread as well and can cause its own set of problems including joint swelling and reproductive issues.
How Does Mycoplasma Spread?
Mycoplasma spreads through multiple routes, which is part of why it is so prevalent in backyard poultry. Direct contact between birds is the most common pathway — an infected bird coughing, sneezing, or simply sharing water and feed with healthy birds can transmit the organism readily. But mycoplasma also spreads through the egg, meaning that hens carrying the infection can pass it directly to their chicks before they hatch — a process called vertical transmission. This is one reason why purchasing chicks or pullets from a reputable, mycoplasma-tested source matters.
Humans can also spread mycoplasma between flocks unknowingly on clothing, shoes, and equipment — which is why biosecurity practices like changing footwear between flocks and avoiding contact with other people’s birds matter more than most backyard keepers realize.
Environmental stress plays a major role in whether an exposed bird develops active symptoms. Birds that are nutritionally deficient, overcrowded, exposed to temperature extremes, or dealing with other health challenges are far more likely to show clinical disease after mycoplasma exposure than well-managed, low-stress birds. This is one of the reasons why many flocks carry mycoplasma without visible symptoms for extended periods — until something stressful tips the balance.
Signs and Symptoms
Mycoplasma gallisepticum (MG) causes a condition commonly called Chronic Respiratory Disease (CRD) in chickens. The signs are predominantly respiratory and can range from subtle to severe depending on the bird’s condition and whether other infections are present at the same time.
Classic signs of MG infection include nasal discharge, foamy or bubbly eyes, swollen sinuses (which can give the face a puffy appearance), sneezing, coughing, and rattling or gurgling sounds when the bird breathes. Affected birds often lose weight, reduce their feed consumption, and drop in egg production. In laying hens, MG can also cause a reduction in hatch rates and eggshell quality.
One hallmark of mycoplasma infections is that they tend to be slow-moving and chronic rather than rapidly fatal. Birds may look mildly unwell for weeks or months, improve somewhat with treatment, then relapse — especially during periods of stress or environmental change. This chronic, on-again-off-again pattern is one of the most useful diagnostic clues that mycoplasma may be involved.
Mycoplasma synoviae (MS) can cause similar respiratory signs but is also associated with infectious synovitis — swelling and inflammation of the joints, particularly the hock joints and footpads. Affected birds may be lame, reluctant to move, or have visibly swollen leg joints. In laying flocks, MS is also associated with eggshell apex abnormalities — a condition where the tip of the egg has a rough, pale, or chalky appearance.
The Critical Point: Mycoplasma Is Forever
This is the most important thing to understand about mycoplasma, and the thing that surprises many new flock owners: once a flock is infected, the birds remain carriers for life, even if they appear healthy and symptom-free. Antibiotics can reduce clinical symptoms and help birds feel better, but they do not eliminate the organism from the bird’s body. A bird that has recovered clinically from a mycoplasma infection is still infected and can still transmit the disease to other birds.
This has significant practical implications. If you introduce new birds to a mycoplasma-positive flock, those new birds will almost certainly become infected. Conversely, if you introduce birds from a mycoplasma-positive flock into a clean flock, you risk infecting your clean birds. This is why quarantine of new birds for a minimum of 30 days — and ideally longer — is so important, and why purchasing from tested, reputable sources matters.
Treatment
Because mycoplasma bacteria lack cell walls, effective treatment requires antibiotics from classes that work differently — specifically tetracyclines, macrolides, and fluoroquinolones. Commonly used options in backyard poultry include:
Tylosin (Tylan) — a macrolide antibiotic available in powder form for mixing into water. It is one of the most commonly used mycoplasma treatments in backyard flocks and is generally effective at reducing clinical signs.
Oxytetracycline — a tetracycline available over the counter in some forms, often used for flock-wide treatment through the water supply.
Doxycycline — another tetracycline, sometimes prescribed by veterinarians for individual bird treatment.
Enrofloxacin (Baytril) — a fluoroquinolone that is prescription-only in the US and not approved for use in poultry intended for food, but sometimes used by veterinarians for severe cases.
It is important to note that in the United States, the use of antibiotics in livestock and poultry is subject to increasing regulatory oversight. Some antibiotics that were previously available over the counter now require a veterinary prescription under the Veterinary Feed Directive (VFD). Always consult a licensed veterinarian before treating your flock with antibiotics, both to ensure you are using the right medication and to stay in compliance with current regulations.
Remember that treatment controls symptoms but does not cure the infection. Birds that respond well to treatment may relapse, particularly during stressful periods, and may need intermittent treatment throughout their lives.
Prevention and Flock Management
Since there is no cure, prevention and management are everything when it comes to mycoplasma. A few key practices:
Buy from tested sources. NPIP (National Poultry Improvement Plan) certification means a flock has been tested and found negative for certain diseases including MG and MS. Purchasing from NPIP-certified flocks significantly reduces your risk of introducing mycoplasma.
Quarantine all new birds. A minimum of 30 days — ideally 4 to 6 weeks — gives you time to observe new birds for signs of illness before they join your main flock. Many experienced flock owners quarantine for 60 days.
Reduce stress. Overcrowding, poor ventilation, temperature extremes, nutritional deficiencies, and the introduction of new birds all stress your existing flock and can trigger clinical outbreaks in birds that were previously subclinical. Good husbandry is your first line of defense.
Maintain excellent ventilation. Mycoplasma thrives in the respiratory secretions of infected birds, and poor air circulation in the coop concentrates those secretions. A well-ventilated coop is one of the simplest and most effective ways to reduce mycoplasma transmission within a flock.
Practice strict biosecurity. Avoid visiting other flocks without changing clothes and footwear, keep wild birds out of your coop and feed areas, and sanitize equipment that travels between birds.
Consider a closed flock. Some experienced backyard keepers who have dealt with mycoplasma decide to maintain a closed flock — not introducing any new birds — as the most reliable way to prevent reintroduction or spread.
When to Call a Vet
If multiple birds in your flock are showing respiratory symptoms, if birds are deteriorating despite treatment, or if you are seeing unusual symptoms like joint swelling or eggshell abnormalities alongside respiratory signs, it is worth consulting a poultry veterinarian. A vet can perform blood tests (ELISA serology) or PCR testing to confirm a mycoplasma diagnosis, rule out other conditions like Newcastle disease or infectious bronchitis, and recommend an appropriate treatment protocol for your specific situation. Many state agricultural laboratories also offer low-cost poultry diagnostic services — contact your state’s department of agriculture for options.
Caring for a backyard flock means learning to navigate health challenges with patience, good information, and the right resources. At Happy Heart Farms we’re committed to helping our customers raise healthy, thriving birds from day one. Browse our full Chicken Care Articles and Resources page for more guides, or call us at 386-208-0495 — we love talking chickens.
~ Grateful hearts make happy hearts ~