Abstract

In the Sudan, 16,540 cattle were surveyed for bovine cutaneous streptothricosis and 48,000 were surveyed for bovine demodicosis. The incidence of cutaneous streptothricosis was 4.5%, while the incidence of bovine demodicosis among the total number of the animals (48,000) surveyed was 34.3% and its incidence among slaughtered animals (1535) was 38.8%. These results show that slaughterhouse surveys for demodicosis are more reliable than clinical surveys because many cattle with demodectic mange might have no visible cutaneous lesions and can only be detected after careful examination, flaying of the hides or during tanning. In both cutaneous streptothricosis and demodicosis many forms of lesions were encountered. The lesions were localised, confluent or generalised involving extensive areas or the whole hide of infested cattle. Dermatophilus congolensis was demonstrated in smears and isolated in pure culture from affected material obtained from cattle infested with cutaneous streptothricosis. Numerous Demodex bovis mites were demonstrated and isolated from caseated (“cheesy”) waxy material obtained from demodectic mange lesions. Severe and advanced histopathological changes were seen in skin sections from the lesions of both diseases. Leather sections from cutaneous streptothricosis showed a badly damaged grain surface with many scars and depressions. The fibres were distorted and had lost their contour; the whole thickness of the crust leather was fibrosed. Leather sections from bovine demodicosis showed, at the site of lesions, a ragged cavity with no definite boundaries. The fibres round the cavity were distorted, thinner than normal and compressed. In some sections, the grain surface was found to be separated from the corium. Hides affected by cutaneous streptothricosis and demodicosis were green-graded as rejects. During the tanning procedure. both diseases caused difficulty in soaking, plumping, splitting, scudding or shaving. At the site of lesions there was uneven distribution of chemicals leaving unsightly blemishes. Both diseases caused a marked reduction in the aesthetic appeal and cutting area of the leather. Cutaneous streptothricosis resulted in a course and rough grain surface and, in severely affected areas, the leather was pitted. Bovine demodicosis caused depressions, cavities or holes in the crust leather. Cutaneous streptothricosis and bovine demodicosis caused a marked reduction in the tensile strength, apparent density and flexing endurance. Bovine demodicosis was found to have the more deleterious effect on crust leather because the percentage decrease in tensile strength, apparent density and flex endurance in the former disease was greater. Hides affected by cutaneous streptothricosis and demodicosis were completely rejected or fetched low prices resulting in serious economic loss.