Veterinary advice should be sought from your local veterinarian before applying any treatment or vaccine. Not sure who to use? Look up veterinarians who specialize in poultry using our directory listing. Find me a Vet

Infectious Synovitis

Other Names: 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). Affected chickens often develop swollen, inflammed hock joints and/or footpads that are warm to the touch and red.

How chickens get infectious synovitis

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 into a flock, usually 100% of the birds eventually become infected, however not all of them may develop clinical signs.

What is the incubation period for infectious synovitis?

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

How is infectious synovitis diagnosed?

Your veterinarian will need to take a culture of the bird's joint fluid. This is done by performing a joint aspiration, where they will remove the fluid from the affected joint using a needle and syringe. Joint aspiration can also relieve pressure due to fluid collecting around the joint. After collecting the sample, your veterinarian will send it to a diagnostic laboratory for testing.

There are several different testing methods offered by 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.

Treatment for infectious synovitis

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 administered in drinking water or feed.

Clinical Signs

Swollen, inflamed (warm and red) footpads and/or hocks
Breast blisters
Ruffled feathers
Shriveled, shrunken, pale comb
Red-blue comb


  • History
  • Clinical signs
  • Physical exam
  • Radiographs
  • Joint fluid culture


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.
AntibioticsIdentified via an antibiotic sensitivity test.



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

  • High rodent populations on the premises.
  • Recent introduction of a new flock member.