Accidental monensin sodium poisoning in a dairy herd in northern Mexico

Monensin sodium is used in cattle to increase feed efficiency. However, intoxications due to overdosage are frequent. This study aimed to report a case of accidental monensin sodium poisoning in an intensive dairy production system in northern Mexico. For the present analysis, 306 five-month-old Holstein-Friesian animals were accidentally fed with a ration containing a high concentration of monensin sodium. These animals manifested symptomatology of diarrhea, depression, anorexia, ataxia, dyspnea, sialorrhea, tachycardia, jugular distension, ruminal atony, edema, and dehydration. In the biochemical analysis, high serum creatine phosphokinase activity was found. Of the intoxicated animals, 82 died (26.79 % mortality). Nine necropsies were performed showing degenerative myopathy with multifocal whitish areas in the heart, hydrothorax, hydropericardium, congestion, and pulmonary edema were found. Histopathological evaluation revealed that 100% presented some type of suppurative or non-suppurative myocarditis, with degeneration of myocardial fibers. Suppurative and necrotic hepatitis was found in the liver. Other important findings were fibrinous, suppurative, or fibrinopurulent bronchopneumonia with fibrinous pleuritis and necrotic vasculitis. 55.55 % showed fibrinoid arteritis and 55.55 % pulmonary congestion and edema. The diet was discontinued and the signs were treated; no further deaths were recorded. Based on such findings, the present study ends with the presentation of a case of monensin sodium poisoning in calves.