Acute arsenic toxicosis in five horses

Five adult horses presented with acute clinical signs of watery diarrhea, excessive salivation, muscle tremors, ataxia, and depression. Four died within 24 hours and the fifth was euthanatized approximately 48 hours after onset of clinical signs. Necropsy finds in two of the horses included hyperemia of gastric mucosa, intestines filled with green to black watery fluid, and multifocal to coalescing, hemorrhagic 1.0-2.0-cm-diameter ulcers of the mucosa of the cecum and large colon. Histopathologic changes in the cecum and large colon consisted of mucosal necrosis and ulceration, vascular thrombosis, necrosis of submucosal blood vessels, and infiltration by mixed mononuclear inflammatory cells and neutrophils. Arsenic toxicosis was suspected. The owner had not been feeding the horses any grain; however, a mixture of grain and pink powder was found in the pasture. Liver arsenic concentrations in the two horses were 14.0 and 11.0 ppm, a sample of renal cortex contained 108 ppm arsenic, and the grain/powder mixture found in the pasture was positive for arsenic at > 3,000 ppm. kidney lead concentrations were 6.5 and 4.2 ppm. Results were consistent with lead arsenate or lead arsenite poisoning.