Experimental poisoning of cattle by the mushroom Ramaria flavo-brunnescens (Clavariaceae): a study of the morphology and pathogenesis of lesions in hooves, tail, horns and tongue.

Seven 2 to 7-mo-old calves were fed the mushroom Ramaria flavo-brunnescens. Clinical signs of toxicosis included salivation, nasal serous discharge, smoothing of the dorsum of the tongue, increased sensitivity in the hooves, reddening of the coronary bands, loss of the long hairs of the tip of the tail, softening of the base of the horns, and progressive weight loss. Affected calves either died or were euthanatized in extremis within 12-37 d from the initiation of feeding. Postmortem examination confirmed changes observed in the live calves. Histopathologic changes were marked in those structures where hard keratinization occurred and there normally is a high uptake of sulfur in the form of cystine during the keratinization process. Toxicosis appeared to alter the metabolism of sulfur-containing amino acids in keratinocytes, particularly cystine, with resultant strength loss in the molecular structure of hard keratin and loosening of the hooves, hairs and horns, and flattening of the lingual filiform papillae.