Phosphine intoxication following oral exposure of horses to aluminum phosphide-treated feed

66 horses were potentially exposed to phosphine (a gas) 14 hours after being fed a pelleted ration treated with aluminum phosphide.

28 horses had clinical signs of profuse sweating, tachycardia, tachypnea, pyrexia, ataxia, seizures, and widespread muscle tremors. Clinically relevant laboratory findings included hypoglycemia and high plasma concentrations of lactate and ammonia and activities of gamma-glutamyl transpeptidase, aspartate aminotransferase, and alkaline phosphatase. At least 4 horses had signs consistent with hepatic encephalopathy. Necropsy findings included petechial and ecchymotic hemorrhages in multiple organs, widespread vascular congestion, hepatic lipidosis, and neuronal necrosis in the brain. Phosphine was detected in the stomachs of the 3 horses tested.

On the farm, horses were treated with gastric lavage followed by administration of di-tri-octahedral smectite, atropine, fluids, and sedatives. Six horses were hospitalized, and lactated Ringer's solution and flunixin meglumine were administered IV. Additionally, 10% dextrose, corn syrup, and di-tri-octahedral smectite were administered PO. Twenty-seven horses died within 2 days after exposure. Two survivors (1 without clinical signs of toxicosis) made a complete recovery.

Progression of clinical signs in affected horses in this report was rapid, with few treatment options available, leading to a high case fatality rate. Fumigation with aluminum phosphide is commonly performed to eliminate weevils and other insects from stored grains. When appropriate precautions are used during fumigation, risk to livestock is typically minimal.