As I think about conversations with swine producers the last few years, incidence of swollen joints and lameness in mid- to late finishing is certainly on the rise. In several cases, Mycoplasma hyosynoviae, a bacterial pathogen we’ve known about for years but didn’t see much, is commonly diagnosed as a contributor to arthritis and lameness in growing pigs.

Frustrating for producers is the reality that often, affected pigs don’t display signs of lameness until significant joint damage has taken place, which diminishes response to treatment and decreases the number of pigs available for that producer’s primary market.

Case Study No. 1

A 2,500-sow, farrow-to-finish producer who flows pigs through wean-to-finish sites has had several groups recently become stiff and move slowly through the pen about six weeks prior to marketing. These signs become progressively worse each week.

During my initial visit, I observed several barns to gain an understanding of the range of severity. Within the first groups to show signs, 20% of pigs were showing one or more of the following signs: sitting with legs outstretched to the side, difficulty rising with some needing assistance and a very tentative gait within the pen. Visually, pigs had no external lesions; some exhibited hock joint swelling.

Activity along with feed and water intake of the rest of the group was normal. Post-mortem examination of four affected pigs revealed that the lungs were visually normal, with no signs of pleuritis or pericarditis. Two pigs had bleeding gastric ulcers. Joints contained a reddish-brown fluid, and the surrounding joint tissue was edematous and inflamed.

Samples were submitted to the diagnostic laboratory. Polymerase chain reaction (PCR) testing for Mycoplasma hyosynoviae was positive on multiple joint samples. Histologic lesions indicated the involvement of Mycoplasma hyosynoviae in joint lesions.

Due to the routine timing of disease onset in this herd, a feedgrade antibiotic program was established prior to the start of clinical signs to reduce disease circulation. The injectable treatment program was also updated so that late finishing options included antibiotics known to have Mycoplasma coverage. As subsequent groups passed through finishing, noticeably less lameness was observed.


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Case Study No. 2

The owner of a 900-sow, farrow-to-wean farm had a number of gilts that in the first three months following arrival at the sow unit became weak in the back legs and eventually were unable to rise without assistance.

This farm receives 150-lb. replacement gilts at an off-site isolation facility where gilts are grown, heat-induced and blood-tested prior to sow farm entry. Gilts have been structurally normal throughout the isolation period.

Upon entry into the sow farm, gilts are individually housed. Some 5-7% of the most recently arrived gilt group had rear-leg lameness when standing. These gilts didn’t seem pained when standing. The next oldest group of gilts showed similar signs, and 3% required assistance to stand. Affected gilts didn’t have an elevated temperature and would eat once assisted to rise.

The standard on-farm treatment regimen for lameness had minimal effect. Post-mortem examination of two gilts revealed few to no internal lesions other than hip joints that looked mildly to severely inflamed and multiple joints that contained a tan-colored fluid.

Diagnostic samples were PCR positive for Mycoplasma hyosynoviae, as were microscopic lesions indicative of Mycoplasma hyosynoviae involvement. No other significant pathogens were isolated.

A gilt acclimation program was put in place for this farm. Cull gilts from the main farm were transported once per month to the off-site isolation unit to be commingled with the newly purchased gilts. During the time when the farm awaited acclimation measures to take effect, all incoming gilts were injected with an antibiotic chosen for its Mycoplasma activity.

Similarly, the on-farm lameness and arthritis treatment guidelines were updated so that animals identified as being lame were individually treated with an antibiotic more effective against Mycoplasma.


The number of cases of arthritis and lameness due to Mycoplasma hyosynoviae has increased among herds. Most common in mid- to late-stage growing pigs, the pathogen can be a primary cause of severe arthritis and lameness.

Carefully consider antibiotic treatment options when dealing with Mycoplasma. Some antibiotics have limited to no activity against this bacteria.

Preventative programs should be in place prior to onset of clinical signs.

If facing increased arthritis and lameness in your growing pig herd, consult your veterinarian so a complete diagnosis can be made to guide treatment and prevention options.