Arthritis

General description

Arthritis is inflammation of the joints, usually in the legs, and leads to permanent changes within the joints.
It is more common in lambs but can affect older sheep.
When multiple joints are affected, the condition is referred to as polyarthritis.
Arthritis is estimated to cost the sheep industry $97 million a year due to poor growth rates and deaths on farm (up to 50% of affected lambs may die from impaired mobility and systemic infection), plus losses at abattoirs due to trimming and condemnations and combined treatment and prevention costs. This makes arthritis the 8^th most costly endemic disease of the Australian sheep industry.
It is estimated that industry could reduce losses by approximately $50 million if optimal prevention was undertaken by all.
Arthritis typically affects between 0.6–3.1% of sheep in affected flocks, with 2.0% the most reported prevalence.

Cause

Inflamed joints can be damaged by infection, often from skin wounds.
Numerous different types of bacteria can cause arthritis in sheep; Erysipelas bacteria are the most frequent cause of arthritis. The bacteria gain access to the body, circulate in the blood stream, settle out and multiply in the joints.
Bacterial arthritis occurs when lambs have a break in their skin, which becomes infected. They then get septicaemia, or blood poisoning, and blood-borne bacteria lodge in a joint.
Often seen in lambs prior to weaning (lamb marking wound infections), but also in older sheep (shearing wound infections).
Short tail docking has been linked to bacterial arthritis in lambs.

Clinical signs

First signs are heat and swelling around one or more joints.
Large joints (such as the knee and hock) are the most affected.
Movement of affected joints is restricted and painful and lambs are obviously lame.
The heat and most of the swelling subsides over a few days but slight swelling, restricted movement and a mild lameness often remain permanently.

Diagnosis

Examining the joints for swelling and heat.
There is often visible bone damage in the joints, the joint fluid becomes thicker and fibrous, the tissues around the joint thicken and there can be pus within the joint.
Arthritis is often not seen in live animals and only discovered in meat processing plants leading to losses due to downgrading, trimming, or condemnation. The average loss per carcase from arthritis is 3kg; more for older affected sheep.
There can be up to a 5% reduction in fleece cut in affected sheep.

Treatment

Early antibiotic treatment can reduce the extent of joint damage, however mob-level treatment is often not practicable. Prevention is the key.

Prevention

A vaccination called Eryvac is available for the prevention of arthritis (but only arthritis due to Erysipelas ssp.). Vaccine is best administered to ewes 4 weeks prior to lambing.
Keep stress at lamb marking to a minimum by choosing a warm sunny day, keeping droving to a minimum before and after marking and allowing the lambs to mother up as soon as possible.
Maintain good hygiene at marking, dipping and any mob intervention or treatment.
Tails should never be docked higher than the third palpable joint.
Do not move sheep immediately after shearing, until wounds are healed. Minimise shearing of terminal lambs

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