NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare.

Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

Ovine Digital Dermatitis

A virulent, rapidly spreading foot disease similar to digital dermatitis in cattle has recently been described in sheep of all ages. The disease is characterised by a high morbidity rate and severe lameness in one or more limb. Unlike scald and footrot, which are characterised by inflammation of the interdigital space, the initial lesion appears to be ulceration of the skin of the coronary band. In some cases the interdigital space is also involved or the hoof wall is under-run and shed to expose the sensitive laminae. It is not uncommon for the entire hoof wall to be shed, exposing sensitive tissue which bleeds profusely when traumatised. Hair loss and ulceration are sometimes seen on the skin below the fetlock joints, which appears similar to ovine viral ulcerative dermatosis lesions. In some cases proliferative lesions at the coronary band appear similar to orf. However, orf virus has not consistently been identified in scab material from the lesions.

UNDER-RUNNING OF THE HOOF WALL FROM THE CORONARY BAND

TYPICAL SKIN LESION ON THE LOWER LIMB

ULCERATION OF THE CORONARY BAND

COMPLETE SHEDDING OF THE HOOF WALL

While some of the lesions associated with ovine digital dermatitis might indicate a viral aetiology, an association has been made between cases of the disease and the presence of motile spirochaetes. However, motile spirochaetes may also be present on the lower limbs of healthy sheep and their contribution to foot diseases is unclear. It has been suggested that Dichelobacter nodosus, which causes footrot, is not involved in the pathogenesis of ovine digital dermatitis.

The response to conventional footrot control measures such as foot trimming and foot-bathing in formalin or zinc sulphate solutions is poor. Lesions heal quickly after topical treatment with aureomycin aerosol sprays, but fresh lesions often develop on other limbs within a few days. There is anecdotal evidence to suggest that regular topical antibiotic treatment or foot-bathing for about 20 minutes in antibiotic solutions is effective for prevention and treatment of ovine digital dermatitis. Alternatively, antibiotic solution can be applied to the limbs of small numbers of sheep in a pen sheep using a pressurised garden weedkiller sprayer. Sheep should be allowed to stand in a dry area afterwards so that the medication can dry onto the feet. Individual cases may also benefit from systemic antibiotic treatment.

Neil Sargison BA VetMB DSHP FRCVS