An outbreak of monensin poisoning in sheep in the State of Rio de Janeiro is described. From 180 animals, eight died after they had been fed with ration containing the ionophore. The poisoning had a variable course and was clinically characterized by apathy, heart arrhythmia, myoglobinuria, incoordenation, incapacity of getting up, and sternal decubitus; one sheep aborted. The macroscopic lesions consisted of pale areas in the myocardium, hydroperitoneum, hydrothorax, and pulmonary edema. Histopathological examination revealed degenerative-necrotic alterations in heart and skeletal muscles. In the myocardium lesions were more severe and were characterized by multifocal necrosis with substitution of the myofibres by fibrous tissue and interstitial mononuclear infiltration. Proliferation of satellite cells and mononuclear inflammatory reaction in skeletal muscles were also verified. It seems that the exaggerated addition of sodic monensin, eventually associated with improper homogenization of monensin in the ration, was responsible for the excessive ingestion of monensin by some animals.
Monensin; toxic miopathy; sheep; pathology
