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Infectious Synovitis

Mycoplasma Synoviae Infection, MS Infection, Enlarged Hock Disease, Synovitis

Infectious synovitis is an acute to chronic, systemic disease of chickens caused by infection with Mycoplasma synoviae (MS). MS is one of the important Mycoplasma species that can infect birds, and infection with MS is listed as a notifiable disease by the World Organization for Animal Health (OIE,

Clinical signs
Early clinical signs of infectious synovitis typically include lameness, stunted growth, and a pale comb. Some chickens may show non-specific signs of illness such as lethargic behavior or depression. Affected chickens often develop swollen hock joints and/or footpads that are also warm to the touch. Other chickens may develop breast blisters. As the disease progresses, affected chickens may present with ruffled feathers, and a shriveled, shrunken comb that in some cases, appears blue-red in color.

Treated chickens often have a slow recovery. There are several antibiotics that can be used, however each with varying effectiveness. The injectable forms of antibiotics have proven to be more effective than those that are administered in drinking water or feed.

Chickens can become infected with MS as early as 1 week of age, however it more commonly occurs in chickens between 4 and 16 weeks of age. MS can be transmitted horizontally, through infectious aerosols coughed and sneezed by infected birds, ingestion of contaminated feed, water, or the environment and/or direct contact with infected birds. MS can also be transmitted vertically, from breeder parents to their offspring, through contaminated laid eggs. However, many flocks that have hatched from MS infected hens have remained free from infection. If MS is introduced in a flock, usually 100% of the birds become infected, however not all of them may develop clinical signs of infection, or become systemic, resulting in the onset of infectious synovitis.

Incubation period
The incubation period for infectious synovitis is approximately 11 to 21 days.

There are several different testing methods offered by veterinary diagnostic laboratories, used for detection of MS infection in chickens. The methods recommended by the OIE for MS detection include bacterial isolation, serological assays, and polymerase chain reaction (PCR). MS isolation is considered to be the gold standard method for MS detection. However it is a slow process and can take up to 28 days to confirm. MS is isolated through the use of a culture performed on a tissue sample, such as joint fluid, from the affected chicken. Other methods include:
  • Serological assays: Serological tests are used to detect the presence of antibodies in the chicken's serum. Serum is the straw-colored liquid fraction of blood plasma from which clotting factors have been removed. There are several serological tests available that are used to detect MS, however due to variations in specificity and sensitivity, they are typically recommended primarily for flock screening, rather than for testing individual birds. Some of the more commonly used tests are the hemagglutination-inhibition (HI) assay, plate agglutination assay, enzyme labeled immunosorbent assay (ELISA), and the rapid serum agglutination (RSA) test.
  • Polymerase chain reaction (PCR) assay: The PCR assay is a molecular based technique which has become increasingly popular. It works by targeting and detecting specific nucleic acid sequences, and is able to provide results in less than 24 hours.

Clinical Signs

Pale comb
Stunted growth
Breast blisters
Warm, swollen hocks or footpads
Ruffled feathers
Shriveled, shrunken comb
Red-blue comb


  • History
  • Clinical signs
  • Physical exam
  • Radiographs
  • Mycoplasma culture
  • FA test
  • PCR
  • qPCR
  • RAPD
  • Necropsy


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.
Tiamulin hydrogen fumarate (hf)A pleuromutilin antibiotic drug that either on it's own or combined with chlortetracycline hydrochloride (hcl)A Garmyn et al., 2017
Tylosin0.5 g/L added to drinking waterK Marx
Spectinomycin HCl0.5-2 g/L added to drinking waterK Marx
Lincomycin HCl2.2 mg/kg (added to feed once a day) or 0.017 g/L (added to drinking water once a day)K Marx



Low to moderate morbidity, with mortality of 1-10%.

Scientific References

Good Overviews

Age Range

It is most common in chickens between 4 and 16 weeks of age

Risk Factors