Emergencies/Illness Health Issues

Mycoplasma Gallisepticum

I had the first necropsy done on one of my birds about 18 months ago and breathed a sigh of relief when she came back negative for Mycoplasma gallisepticum (MG). That’s because once it’s in your flock it’s there to stay whether you can see it or not.

Mycoplasma are a genus of tiny bacteria that cause compromised immune systems and respiratory disease in their affected hosts. They’re unique in the world of bacteria because they lack a cell wall, which makes them resistant to many common antibiotics that work by targeting cell wall synthesis.

The Mycoplasma family includes more than 100 species, each infecting a specific animal species. 17 are found in poultry; two of which cause disease in chickens.

MG is primarily a respiratory infection and is becoming more common with the increased popularity of backyard flocks: more people are keeping chickens and mixing birds from different sources.

It often occurs in chickens that are co-infected with other pathogens (i.e. E. coli or Infectious Bronchitis); are stressed (e.g. changes in the pecking order, integrating into a new flock); nutritionally deficient; or live in coops with high levels of ammonia or dust. Chickens can become infected several days after exposure, but remain asymptomatic for months.


  • Vertically from infected hens to their chicks through the egg.
  • Direct contact between birds in a flock through shared feed, water and the environment: spread through breathing in aerosolized droplets from coughing or sneezing.
  • Indirect contact on fomites (crates, contaminated shoes, hands, equipment).


  • Primary areas of initial infection: eyes, nasal passages, sinuses and trachea.
  • Difficulty breathing.
  • Coughing, sneezing, gasping.
  • Sweet smelling nasal discharge.
  • Stained facial feathers.
  • Foamy bubbles in the eyes.
  • Swollen eyelids and sinuses (sinusitis).
  • Decreased egg production.
  • Severe infection may also involve the bronchi, air sacs or lungs.
  • Many birds with respiratory viruses are also co-infected with E. coli, which cause severe thickening and accumulation of fluid around the air sacs; inflammation around the heart and liver.
  • In cases where there are no other underlying health issues symptoms of illness are common, but the death rate is low.


  • Most strains of MG respond to broad-spectrum antibiotics including Tylosin, Tetracyclines and Denegard; but not to penicillin or antibiotics which target the cell wall.
  • Tylan Soluble is more effective in younger than older birds, unless given at the early stages of the disease.
  • Sadly, birds that are still symptomatic after treatment are usually euthanized because MG will be too deeply entrenched within the air sacs and hollow bones to be removed.
  • Medications treat the symptoms, but are not a cure.
  • Once infected most birds are considered carriers for life.


  • Purchase birds from known MG-free flocks.
  • Obtain vaccinated birds.
  • Practice good management and biosecurity.
  • Quarantine new birds for least 2-3 weeks.
  • Understand the chain of infection and FLAWS.
  • Ensure your coop is well ventilated, keep dust and ammonia levels low. Ammonia paralyses the small hairs (cilia), which act like an escalator to move normal mucus up the trachea before being swallowed.
  • Clean and disinfect your coop, waterers and feeders often. MG can be killed with Virkon, Phenolic disinfectants and 70% ethanol.
  • Provide a stress-free environment (i.e. not overcrowded, no changes in the pecking order). Give probiotics and vitamins to birds that are stressed.
  • Prevent birds from getting chilled or heat stress.
  • Always treat sick birds; they are more vulnerable to later becoming infected with MG.
  • Provide a high quality, balanced diet.
  • If hens are kept symptom-free the risk of passing MG to their chicks through the egg is reduced.
  • Be vigilant about carrying potential pathogens from your adult birds to chicks that are more vulnerable.
  • If chicks are exposed to a mild bout of MG they will acquire some immunity as long as they are otherwise healthy.
  • Apple cider vinegar helps strengthen the immune system and keeps water containers cleaner. Use one week per month, more often if diseases are present.

What does it mean if you have a bird that tests positive for MG? Once you’ve had the pathogen in your flock assume that all birds are potential carriers and will be for life, regardless of whether they show any symptoms or not. You have a couple of options: euthanize your entire flock, disinfect your coop and all your equipment and start from scratch or keep a ‘closed’ flock with the following limitations: you can’t re-home any of your birds or bring any new birds (including your own chicks) into your flock, unless they have been vaccinated against MG. When all those birds have died you can then start over with new birds.

You must practice strict biosecurity when going between your flock and another. You can easily carry MG on your shoes or clothes. The same applies to visitors to your property – they must be careful not to transport pathogens back to their flock.

As you can see, the choices are limited and difficult. Prevention is always easier. If you are new to chickens, get all your birds from the same source, at the same time. Be happy with the birds you’ve got and work hard to keep them healthy and stress free. If you are a veteran chicken keeper and have an MG-free flock do everything you can to keep it that way. It is so easy for an unseen pathogen to infect your flock and there are no do-overs.

Credits: Merck Veterinary Manual and NADIS Animal Health Skill.                            Featured photo: NADIS

1 comment on “Mycoplasma Gallisepticum

  1. I love your site. So informative. Thank you so much for all you do!

    Liked by 1 person

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