Chronic Methylmercury Toxicosis in Calves

Abstract

SUMMARY Clinical signs, lesions, and tissue residues were determined in 5 calves after the feeding of graded amounts of a methylmercury product over an extended period. Between the 35th and 91st days of the study, 3 of the calves developed clinical signs of toxicosis characterized by a sudden onset of ataxia and neuromuscular incoordination, which progressed rapidly to convulsions and a moribund state. Gross morphologic lesions were minimal. The histopathologic changes were principally a reduction in the number of cells in the cerebellar granular layer and toxic nephrosis involving the proximal convoluted tubules. The rates of mercury deposition in blood plasma, erythrocytes, and hair varied throughout the experiment. Mercury residues in tissues at necropsy were not correlated with the cumulative amount fed or the onset of clinical signs but were relatively consistent for each calf when the residues in samples of hair, liver, kidney, brain, and semitendinosus muscle were compared.