Polyarthritis in Pigs: Multiple Swollen Joints and Stiffness

Polyarthritis means inflammation affecting multiple joints at the same time. In pigs, this can cause swollen knees, hocks, elbows, or other joints, along with stiffness, pain, and a short, careful gait. Some pigs look mildly sore at first. Others become reluctant to stand, walk, or keep up with normal activity.

This is not one single disease. Instead, polyarthritis is a clinical problem with several possible causes. In pigs, infectious causes are especially important. Bacteria such as Erysipelothrix rhusiopathiae, Streptococcus suis, and Glaesserella parasuis are well-recognized causes of joint disease, and Mycoplasma hyosynoviae is strongly associated with arthritis in older nursery and growing pigs. Less often, trauma, poor footing, or developmental orthopedic problems can add to the picture.

For pet pigs, the biggest concern is whether the joint swelling is part of a systemic infection. A pig with painful joints may also have fever, poor appetite, lethargy, or weight loss. Because several of the important causes can spread within groups of pigs or lead to lasting joint damage, it is best to involve your vet early rather than waiting to see if the stiffness passes on its own.

In pigs, polyarthritis is often linked to infection spreading to the joints through the bloodstream. One important cause is swine erysipelas, caused by Erysipelothrix rhusiopathiae. Merck Veterinary Manual notes that erysipelas can cause septicemia, arthritis, and endocarditis, and chronic cases commonly produce lameness and slowed growth. Other important bacterial causes include Streptococcus suis and Glaesserella parasuis, both of which can be part of broader systemic disease.

Mycoplasma-associated arthritis is another common pattern. Merck lists Mycoplasma hyosynoviae as a well-known cause of hind-limb arthritis, especially in pigs around 10 to 26 weeks of age. Mycoplasma hyorhinis is more often associated with arthritis and polyserositis in younger nursery pigs. These organisms may already be present in a herd, and stress, mixing, transport, crowding, or other disease can make clinical signs more likely.

Not every stiff pig has infectious polyarthritis. Trauma, slippery flooring, rough handling, hoof problems, developmental joint disease, and excess body weight can all contribute to soreness or lameness. Still, when several joints are swollen at once, your vet will usually want to rule out infectious causes first because they can progress quickly and may affect other pigs in the household or group.

Diagnosis starts with a hands-on exam. Your vet will look at how your pig stands and walks, feel the affected joints, check for heat and swelling, and look for clues such as fever, skin lesions, poor body condition, or signs of illness in other body systems. History matters too. Age, recent stress, new pig introductions, vaccination status, and whether other pigs are affected can help narrow the list.

Testing depends on how sick the pig is and what causes are most likely. Your vet may recommend bloodwork, radiographs, and in some cases ultrasound or advanced imaging if a specific joint is badly affected. For suspected infectious arthritis, joint fluid or joint tissue sampling can be especially helpful. Merck notes that diagnosis for erysipelas may be based on culture of fresh tissues, fluid, or blood, or molecular testing, and that Glässer disease is diagnosed by compatible signs plus isolation or PCR detection of Glaesserella parasuis from affected pigs.

For Mycoplasma-related arthritis, PCR testing on joint fluid, joint swabs, synovial membrane, or related samples may be used by diagnostic laboratories. Because some of these organisms can live in healthy pigs without causing disease, your vet may combine test results with the exam, age of the pig, and herd or household history before deciding what is most likely.

The goal is not only to confirm arthritis, but also to decide how aggressive treatment needs to be and whether there may be a contagious or herd-level issue. That is why early veterinary evaluation is so useful.

Prevention focuses on reducing infectious disease pressure and lowering joint stress. Good sanitation, dry bedding, appropriate stocking density, careful introduction of new pigs, and prompt treatment of wounds can all help. Slippery floors and rough surfaces increase falls and joint strain, so secure footing matters too, especially for heavier pet pigs.

Vaccination may be part of prevention in some situations. Merck Veterinary Manual states that vaccines are generally effective for preventing acute swine erysipelas, and it also emphasizes sanitation, hygiene, and removal of clinically affected pigs as useful control measures. Your vet can help decide whether erysipelas vaccination makes sense for your pig based on lifestyle, exposure risk, and local disease patterns.

Because some causes of polyarthritis are linked to stress and mixing, it also helps to avoid sudden social disruption, overcrowding, and poor ventilation. Quarantine new pigs before introduction when possible. If one pig develops swollen joints, fever, or unexplained lameness, early veterinary evaluation can protect both that pig and any companions by catching a potentially infectious problem sooner.