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Chronic Respiratory Disease

Other Names: Bulgy Eye, Mycoplasmosis, MG, CRD, Chronic Respiratory Disease (CRD)

Chronic respiratory disease is an upper respiratory infection caused by Mycoplasma gallisepticum. The disease occurs very commonly in backyard chicken flocks worldwide. Young birds less than 4 months of age, and roosters, tend to have more severe infections than older or adult birds. The characteristic signs include tracheal rales or gurgling sounds, nasal discharge, sneezing, gaping, and coughing. Conjunctivitis and eye discharge may be present in one or both eyes. There can less commonly be facial swelling and head shaking.


Sources of infection include latently and chronically infected birds (domestic chickens and turkeys or wild birds). It spreads vertically (from breeding parents to offspring) and horizontally both directly from bird to bird and can be indirectly spread by living and inanimate vectors. Within a flock the spread of the pathogen is normally slow.


There are several common laboratory tests used to detect M. gallisepticum in chickens that are offered by numerous veterinary diagnostic laboratories. Two of the most popular include:
  • A real-time polymerase chain reaction (rtPCR) procedure which is conducted on tracheal and/or oropharyngeal swabs of clinically ill birds. This provides direct confirmation of the presence of the M. gallisepticum pathogen.
  • Hemagglutination inhibition (HI) which is an indirect test that's performed on serum samples collected from birds that usually have been ill for a short period or have had clinical symptoms from which they have recovered. If the test comes back positive for antibodies, a presumptive diagnosis of chronic respiratory infection can be made.


Several antibiotics can be used to treat mycoplasma infections in chickens: macrolides, lincosamides, aminoglycosides, tetracyclines, floroquinolones, and pleuromutilins.

Clinical Signs

Eye discharge
Gurgling sounds
Nasal discharge
Facial swelling
Head shaking
Tracheal rales


  • History
  • Clinical signs
  • Lab testing

Reported Cases

  • Case 1: Severe Infraorbital sinusitis in a Pheasants Pasteurella multocida, somatic serotype 6, was isolated from the infraorbital sinuses of 8-wk-old ring-necked pheasants with severe sinusitis. In addition, Escherichia coli, Pasteurella haemolytica-like bacteria, Mycoplasma gallinaceum, and Mycoplasma glycophilum were also isolated from some of the sinuses. Clinical signs appeared 3 days after placement on the grow-out ranch. The sinusitis consisted of severe unilateral or bilateral distention of the sinuses by mucoid to caseous exudate. Mortality and morbidity were low. Birds responded to treatment with tetracycline after proper medication procedures. The source of the infection was not determined, though possible sources include the brood ranch, wild animals, or wild waterfowl. Ref


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Doxycycline (Vibramycin)25-50 mg/kg PO q12-24h x 21 daysB Speer
Lincomycin/spectinomycinAdministered orally (50 mg/kg q24h), or in drinking water (528 mg/L for 3-7 days)B Speer
Tiamulin (Denagard)25-50 mg/kg administered orally q24 x 3 daysB Speer
TilmicosinAdministered orally (30 mg/kg q24h) or in drinking water (100-500 mg/L) x 5 daysB Speer
Tylosin (Tylan)Administered IM (15-30 mg/kg q6-12h), or in drinking water (50 mg/L)B Speer
Baicalin450 mg/kg of feedZ Wu et al.,2020
Baicalin (Scutellaria baicalensis) extract450 mg/kg of dietJ Bao et al., 2021; Z Wu et al., 2019, 2020; M Zou., et al. 2021; M Ishfaq et al., 2019, 2021; J Li et al 2019; Y Wang et al. 2022; F Yang et al., 2020; Y Zhou et al., 2019; B Yin et al., 2021; M Bao et al., 2022; Z Hu et al., 2022
ProbioticsWhen added to the diet of chickens infected with Mycoplasma it alleviated lung inflammation injury caused by the infection and increased their defense against Escherichia coli by improved gut microbiota composition.J Wang et al., 2021
Licorice (Glycyrrhiza glabra)Can inhibit MG-triggered inflammation and apoptosis by suppressing the expression of MMP2/MMP9 through the JNK and p38 pathways and inhibit the expression of virulence genes to resist MGM Alagawany et al., 2019; Y Wang et al., 2022; M Abo-Samaha et al., 2022



  • Minimize contact with wild birds.
  • Quarantine any new flock members, or any birds taken to a poultry show, swab, county fair, auction, etc. for 30 days prior to adding them to your flock.
  • Minimize stress.

Scientific References

Good Overviews

Age Range

Younger birds are affected more severely then adult birds.

Risk Factors

  • Bringing chickens to or purchasing chickens from poultry auctions, swap meets, shows, county fairs, or other large poultry-associated events.
  • Contact with wild birds.