Fatal cardiomyopathy in feedlot sheep attributed to monensin toxicosis

Three outbreaks of fatal cardiomyopathy in feedlot sheep are reported which were associated with the introduction of pelleted feed that contained greater than recommended concentrations of monensin. Gross and histopathological examination of some of these sheep revealed evidence of cardiomyopathy. Myocardial lesions which had a predominantly epicardial distribution are described. Lesions were also observed in skeletal muscle and in brain.