Reports of zinc phosphide poisoning in sheep in Fars province

Abstract

Zinc phosphide is a rodenticide that has been used since the 1930s. Formulation and especially those found in over-the-counter preparations, contain 2 and 5 percent zinc phosphid mixed with wheat, oats. Sometimes in Fars province it is called Black Wheat. Zinc phosphide rapidly forms phosphin gas in acidic conditions. The exact mechanism of action is not clear, but phosphin has been shown to block cytochorom oxidase and thus, oxidative phosphorylation is inhibited and energy-producing processes in mitochondria is blocked which results in cell death. These reports describe three episodes of zinc phosphide poisoning of sheep in different areas of Fars provice. In one episode farmer added zinc phosphide wheat-mixture to oat barn and it accidentally fed to sheep. Clinical signs and mortality was started immediately after feeding. Out of 215 adult sheep, 38 died and 16 showed clinical signs of poisoning. In another episode farmer used this poison for rodent control in a wheat farm. Sheep browsed on the residue of wheat straw. A number of sheep died and some showed clinical signs of toxicity one day after grazing. Out of 350 adult sheep, 62 sheep died and 31 sheep showed clinical signs. In the third episode three sheep’s carcasses and eight sick sheep with zinc phosphide poisoning signs were referred to Shiraz Veterinary Teaching Hospital. Clinical signs in three above reports included severe depression, tachypenea, expiratory grunt, salivation, epiphoria, ruminal tympany, ataxia, weakness, recumbancy and struggling. Necropsy finding included incomplete rigor mortis and putrefaction, phosphine gas odor from rumen, observation of black wheat in ruminal contents, hemorrhage and congestion of ruminal, omasal and abomasal walls, Liver and kidney congestion and lung edema and congestion. Treatments were instituted by fluid therapy, antacid (sodium bicarbonate) and laxatives (magnesium sulfate and paraffin) administration for standing animals. The extensive use of poison is a warning issue and it was concluded that history, clinical signs and necropsy findings are necessary for diagnosis.