Chronic Respiratory Disease/Mycoplasma Gallicepticum

Chronic Respiratory Disease is a slow spreading and long lasting respiratory disease that is  can lay latent with no symptoms for long periods until times of stress cause it to appear, which can make it more difficult to diagnose.  It can be passed slowly through a flock and is also complicated because it can be passed to the next generation through the egg.  



  • Chickens 
  • Pigeons
  • Game birds
  • Pheasants
  • Quail 
  • Turkeys (Called Infectious Sinusitis)
  • Peafowl

Where:  Worldwide

When: 3 weeks through adult

Why:  Mycoplasma


  • Breeder to Egg
  • Air
  • Water
  • Direct Contact


            Common Symptoms:

  • May be no symptoms
  • Sneezing
  • Coughing
  • Rattled Breathing
  • Facial Swelling
  • Nasal Discharge
  • Bubbly Eyes
  • "Squeaky Crow"
  • Weight Loss
  • Yellowish droppings
  • Ruffled Feathers
  • Droopiness
  • Loss of appetite

            Other Symptoms:

  • Dark head
  • Drop in Egg Production


Treatment: Antibiotics will only treat the symptoms, but will not prevent spread.  A long-term treatment with antibiotics will result in a resistance to it and is not recommended.  The only way to guarantee a stop to the spread is to cull the flock, which is not always practical. 

  • Tylan - 1/2cc under skin at neck for 5 days
  • Tetracyclines
  • 2t of VetRX /gallon of water for flock treatment
  • Egg can be treated with antibiotics or heat (not as effective) to prevent passage to the next generation. 


  • Buy MG-free birds
  • Reduce stress in the flock after showing, during weather changes after worming  and after vaccination.
  • Avoid drafts, crowding, ammonia fumes and chilling
  • Disenfect housing and leave vacant for several weeks.

Vaccine:  Yes (click here for more information) 

  • Typically vaccination of young birds (<2 months).  
  • Older birds can be given vaccine as a booster.  


Also Known As: 

  • The Stress Disease
  • CRD
  • MG
  • PPLO 
  • Plueropneumonia-like Organism
  • Mycoplasmosis (one form of it)

Affects:  Sinuses, Trachea, Air Sacs 

Clinical Diagnosis:  Diagnosis by laboratory testing of blood/plasma.

Diseases with similar symptoms: Similar symptoms, but CRD spreads much more slowly within the flock.

  • Infectious Coryza
  • Fowl Cholera
  • Infectious Bronchitis
  • Newcastle Disease

Duration of symptoms:  7 to 21 days, however it can be longer.

Incubation:  As little as 14 days. 

Morbidity:  High (Nearly 100%) occurrence in birds that have not been vaccinated.   

Mortality:  Often low, but higher in young birds.

Transmission to people:  No. 


Damerow, Gail (1994) The Chicken Health Handbook. North Adams, MA: Storey Publishers

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A righteous man cares about his animal's health...

Proverbs 12:10a