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This article was published in 2005
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Arthritis in lambs
Sarah Robson, Acting SRAHM, Wagga Wagga, NSW DPI
Arthritic or "crippled" lambs are a common problem for most lamb producers, but the extent of the problem varies widely. Depending on the cause, producers may have one or two animals out of a mob affected each year, up to 10% of a mob affected, or in severe situations 100% affected.
Arthritis in lambs can be caused by a variety of bacteria. When the occasional lamb is 'crippled' with arthritis it is usually because it has had an infection from a contaminated wound, or from an infection of the navel cord. The infection lodges in the joints and arthritis results. This type of arthritis can be prevented by minimising the chance of bacterial contamination of the navel and of marking and mulesing wounds, and encouraging fast wound healing.
Lambs that receive adequate colostrum from their dams and are well nourished will have a stronger immune system and will be less at risk of developing an infection. They will usually heal faster after marking and mulesing.
Lambing into a well grassed paddock with minimal faecal contamination will reduce the risk of navel infection.
Maintaining a high standard of hygiene at lamb marking and mulesing is very important. The use of temporary yards in a clean, well grassed paddock is recommended. Instruments should be kept clean, and disinfectant solutions used to soak instruments should be changed frequently. The operation is ideally carried out in mild weather with few flies around. Lambs should be left undisturbed for 3 to 4 weeks after mulesing so wound healing is not impaired.
There are two other forms of arthritis that we see commonly where there is an "outbreak" of arthritis in a significant proportion of the flock. These forms can result in substantial economic loss. Set back in growth, treatment costs (time, labour and cost of medication), culling of affected lambs, and carcass condemnation contribute to economic loss.
Erysipelas arthritis is usually seen 10 to 14 days after marking and mulesing. It is therefore more common in merino lambs. Affected lambs have a fever and are very lame, despite no obvious joint swelling. Some lambs will recover but some progress to be permanently crippled.
The bacteria causing this form of arthritis, Erysipelothrix rhusiopathiae, is found in the environment. It survives in soil, faeces, water, and decaying organic matter. It has also been found to survive in dip fluid and can cause arthritis in sheep that are dipped off-shears by contamination of shearing wounds. As Erysipelothrix is in the environment, poor hygiene at marking and mulesing and soil/faecal contamination of marking and mulesing wounds has traditionally been blamed for high levels of infection.
Recent research in Western Australia by Dr Michael Paton has revealed that many producers following hygienic practices and using portable yards for marking and mulesing are still experiencing problems with Erysipelas arthritis. This has led to the speculation that the source of the bacteria on such properties may be the sheep rather than the environment. There has not been enough work done in sheep to prove this theory yet, however it is known that in pigs, Erysipelothrix bacteria is present in the mouth and throat of healthy animals. If this is the same for sheep we would expect that the bacteria is already present in the lamb's mouth. Under conditions of stress such as marking, mulesing or shearing, the bacteria could multiply and pass into the blood stream. This will cause generalised infection which may ultimately result in arthritis. Contamination of wounds is still a major contributor to post-mulesing arthritis and definitely shouldn't be ignored, but this research shows that it can still be a problem despite doing everything right.
A vaccine to prevent erysipelas arthritis is available. Anecdotal evidence suggests that this vaccine is very effective. One producer in the Wagga RLPB district has been using the vaccine for almost a decade and he now sees only one or two lambs with arthritis, whereas he had approximately 10% of his lambs affected by arthritis prior to the use of the vaccine. A pilot trial to test the effectiveness of the vaccine is underway in the Condobolin RLPB, with a view to commence a wider trial in the near future.
Chlamydial arthritis can be a significant problem, particularly for prime lamb producers. The disease is most common in lambs 4 to 6 months of age. Typically there is a sudden onset, affected animals separate from the mob, are depressed and reluctant to move, display marked lameness in one or more limb and dramatic loss in condition. Joint swelling occurs later in the course of the disease. Outbreaks usually last for 8 weeks. In some cases 100% of a mob can be affected. If treated early with antibiotics the lambs can recover. This is a labour-intensive process. Some producers report that some affected lambs recover without treatment; others report that without treatment affected lambs don't recover and remain permanently lame.
Despite this type of arthritis being common in many flocks, very little is known about how lambs contract the disease and what factors lead to an outbreak. A research project commenced in the southwest slopes last year to try to answer these questions. With knowledge of how the disease is spread, producers may be able to prevent the disease in their lambs. Samples have been collected to isolate the infectious agent. If the same strain of Chlamydia is causing disease across a range of properties, an opportunity exists to develop a vaccine to prevent the disease. Due to unforeseen delays in the establishment of a specialised chlamydial culturing laboratory, preliminary results have taken longer than anticipated but should be available by the end of the year. Surveys to elucidate how lambs become infected are ongoing.