Systemic granulomatosis associated with hairy vetch toxicosis in a cattle herd.

An outbreak of severe nodular to diffuse dermatitis affecting black yearling cattle occurred on a northeast Colorado farm. The outbreak took place during early summer and resulted in the death of nineteen animals, while several others exhibited symptoms of declining appetite, rough, scaly skin, and chronic weight loss. Physical examination findings included poor body condition, hyperthermia, pruritus, and superficial lymphadenopathy. The outbreak was restricted to animals grazing on abandoned farmland, and no improvement was noted following symptomatic treatment. Postmortem examination revealed marked lymphadenopathy with pale raised foci and streaks on the external and cut surfaces of the skin, kidney, spleen, and liver. Histologic evaluation of skin sections showed severe nodular to diffuse granulomatous dermatitis with eosinophils and multinucleated giant cells. Similar eosinophilic granulomatous inflammation was also observed in sections of the kidneys, liver, and spleen. These results were consistent with systemic granulomatous disease, highly suggestive of hairy vetch toxicosis, as the affected animals had been grazing on a pasture containing hairy vetch.