Zinc phosphide is an inorganic compound that combines phosphorus with zinc. It is used in rodenticide baits. When an animal eats the bait, the acid in the animal’s stomach turns the zinc phosphide into phosphine. Phosphine is a very toxic gas. Phosphine is also released by aluminum phosphide and magnesium phosphide. These are used as fumigants in stored grain.

There is evidently no way to identify this grain mixture, and bait ingestion has resulted in lethal exposure to a number of horses. The clinical effects of aluminum phosphide, used as a grain fumigator, are similar to those of zinc phosphide.