Effects of concurrent oral administration of monensin on the toxicity of increasing doses of selenium in lambs.

The effects of concurrent administration of monensin sodium on the toxicity of progressively increasing oral doses of selenium (0.2 to 2.4 mg per kg body weight), given as sodium selenite twice weekly, have been examined in growing lambs. To link the chemically determined selenium concentration in tissues with observable pathological changes, the histochemical method of Danscher, which visualizes selenium bonds within tissues, was utilized. Findings included damage to conduction and contractile myofibres in the heart, segmental sarcoplasmal necrosis with lysis and atrophic change in skeletal musculature and selective accumulation of Danscher reaction-product in damaged areas of the liver, kidney and secondary lymphoid tissue. Concurrent administration of monensin sodium at a constant safe dosage enhanced the toxicity of selenium as demonstrated by increased severity of the signs of intoxication, fatalities, tissue selenium concentrations and intensified gross, histopathological and histochemical changes.