Nadis report - Foot rot

There is increasing evidence that a high prevalence of lameness (greater than two per cent) is indicative of failure to treat lame sheep appropriately (not quickly enough and using the wrong treatment). One flock study reported an annual loss of around £6 per lame sheep affected by foot rot.

Clinical Signs

Inflammation and superficial infection of the interdigital skin extends to under-run the sole and hoof horn of the inner hoof wall. Further separation and under-running of the hoof horn of the sole continues and may extend to the outer hoof wall. There is a characteristic smell of necrotic horn/exudate.

The whole hoof capsule may be shed in severe cases. Chronic infection leads to grossly mis-shapen and overgrown hooves.

In chronic cases, the hoof walls and toes become overgrown and mis-shapen, trapping dirt and inflammatory exudate between the inflamed, granulating soft tissues of the sole and overgrown horn.

Diagnosis and treatment

Diagnosis of foot rot is based upon the characteristic appearance of lesions.The best current treatment for foot rot is an injection of long acting oxytetracycline injected intramuscularly at a dose rate of 10 mg/kg, together with removal of any debris from the interdigital space and use of an antibacterial spray. Affected sheep must be isolated with other sheep undergoing similar treatment.

• Removal of any debris from the interdigital space

• Injection of long acting oxytetracycline

• Oxytetracycline spray

• No foot paring

• Cull chronic cases that fail to cure after three treatments.

Paring the hoof horn to expose the lesion exposes the corium and delays healing. Overzealous paring and exposure of the sensitive corium in combination with frequent formalin footbath treatments may result in the generation of toe fibromas.

Foot paring in cases of foot rot:

Foot paring may be undertaken when the sheep is no longer lame and the foot is grossly overgrown. The grossly overgrown horn should be trimmed with sharp foot shears after about one week when the foot rot lesion is much less inflamed. If foot paring is done before this it can:

• Cause pain

• Delay healing

• May cause toe granulomas

Prevention and control

Foot trimming

Foot trimming has no role in the treatment of foot rot nor should it be considered as a preventive method when planning control programmes.

Footbathing sheep before housing and after gathering, where facilities are excellent and the standing is hard can kill off bacteria on the surface of the foot and reduce transmission of infection. Footbathing is most likely to be successful to prevent foot rot.

Trimming excess horn whilst leaving a weight-bearing wall is best done once the sheep is no longer lame; trimming should not be viewed as part of the treatment for foot rot. If a chronically lame sheep does not respond to remedial treatment, it should be culled.

All purchased stock must be quarantined for one month and examined for foot rot before introduction into the main flock. Footbathing could be undertaken during this quarantine period as directed by the farmer’s veterinary surgeon.

Prevention measures

Measures to prevent foot rot include:

• Closed flock

• Quarantine all introduced sheep

• Consider use of vaccine

• Regular footbathing (but not as a treatment option).

Vaccination

There are few reported flock trials of foot rot vaccines in the UK upon which to base informed opinion. It is recommended that all sheep are vaccinated thereby limiting future environmental contamination and challenge. Subsequent doses should be administered according to prevailing conditions or in anticipation of climatic conditions which favour disease. Potential disadvantages associated with vaccination include; cost, short duration (booster vaccinations required every six months or before the anticipated challenge period), and occasional severe localised reaction at the injection site.