Acute nitrate/nitrite poisoning in cattle caused by ingestion of Tithoniatubaeformis.

An outbreak of acute mortality affecting 13% of a herd of 450 beef cattle is described in the province of Salta, Argentina. The incident occurred after the introduction of the herd into a paddock that had previously been used for cattle confinement. Approximately 8 h after being introduced into the paddock, the affected animals developed hyperacute clinical signs, including weakness, ataxia, tachycardia and brown mucous membranes, followed by death within minutes. The autopsy findings included poorly coagulated dark chocolate-brown blood and generalized congestion, consistent with methemoglobinemia. The paddock vegetation was almost entirely composed of Tithonia tubaeformis. Diphenylamine tests on rumen contents, aqueous humor and plant material were positive for nitrates. This is the first report of T. tubaeformis as a cause of nitrate/nitrite poisoning.