SEVERE FOOT LAMENESS IN CATTLE ASSOCIATED WITH INVASIVE SPIROCHETES

One hundred (25%) of 400 cattle on a feedlot unit were affected with a sudden-onset lameness over a period of six weeks. The condition was s een in bulls, heifers and bullocks. Typically, one or two cattle in a pen of 20 presented with severe lameness; within 72 hours up to half o f the cattle in the pen were similarly affected. The first eases to oc cur were treated with topical and systemic oxytetracyclines, tylosin a nd penicillin and streptomycin. However, the response to treatment was poor and, because of rapid weight loss, a decision was made to cull a ll affected cattle as they presented. The condition in any particular animal usually involved a single limb, either fore or hind, and affect ed animals exhibited a marked reluctance to bear weight on the limb in volved. There was swelling of the coronary band, fissuring of the inte rdigital skin and development of granulation tissue within the fissure s. Spirochaetes were demonstrated on examination of direct smears made from the lesions and Bacteroides melaninogenicus (prevotella melanino genica) was isolated on cultural examination. The histopathological ch aracteristics associated with the condition included a widespread kera tinocyte degeneration within which were present variably-sized bright eosinophilic intracytoplasmic inclusion bodies. Ultrastructural examin ation of these inclusions suggested that they consisted of amorphous i ntracytoplasmic debris; viral particles could not be identified. Attem pts to demonstrate virus on electron microscopic examination of negati vely-stained preparations made from lesions and attempts to culture vi rus from all lesions were unsuccessful. However, numerous spirochaetes were present within the cytoplasm of affected keratinocytes; a role f or these organisms in the aetiology of this condition seems likely.