ABSTRACT: Monosodium methanearsonate (MSMA) is an organic form of arsenic present in the formulations of some herbicides. Accidental ingestion of pasture contaminated with arsenic may lead to toxicosis in cattle. Almost 200 head of cattle maintained in an area sprayed with MSMA presented with intense diarrhea and dehydration after grazing. Subsequently, 16 of these animals died. Toxic levels of arsenic (>1.5????g/g) were detected in the kidney, liver, urine, and skeletal muscle of 6 animals. At gross inspection were observed multifocal to coalescent ulcers in the mucosa from on the forestomachs associated with hemorrhagic areas and marked wall edema. Microscopic examination mainly showed fibrinoid necrosis of vessels with multifocal thrombosis associated with ischemic infarction that were characterized by large transmural necrotic areas in the forestomachs. The clinical and pathological changes interestingly showed that this form of arsenic although considered less toxic, has caused severe vascular injury in forestomachs of cattle.
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