A chronic cardiomyopathy in feedlot cattle attributed to toxic levels of salinomycin in the feed.

The clinical signs and pathology in an outbreak of toxicity in feedlot cattle attributed to the ingestion of toxic levels of the ionophore antibiotic salinomycin over an extended period of 11 weeks are described. Thirty-nine out of 380 cattle developed signs consistent with cardiac failure and 8 of these died. Clinical signs included dyspnoea, tachypnoea, tachycardia and exercise intolerance. Two cattle were necropsied and in one there were macroscopic lesions suggestive of congestive heart failure, namely pulmonary oedema, hydrothorax and hepatomegaly. Histopathology revealed a chronic cardiomyopathy characterised principally by extensive myocardial fibre atrophy with multifocal hypertrophy and interstitial and replacement fibrosis. Hepatic and pulmonary lesions were consistent with those of congestive cardiac failure. The myocardial lesions in this outbreak were similar to those encountered in cases of a chronic toxicity associated with the ingestion of litter derived from poultry rations containing ionophores (ionophore-associated poultry litter toxicity). Hence, the clinical and pathological findings in this outbreak indicate that in cattle, the prolonged ingestion of ionophores over several weeks may result in the development of chronic myocardial lesions comparable to those of IAPLT but significantly different from those encountered in the more traditional acute outbreaks of ionophore toxicity as described in the literature.