Cyanide (also referred to as prussic acid and hydrocyanic acid) poisoning occurs sporadically in grazing cattle. Cyanide is a rapid acting toxin which inhibits the use of oxygen by the cells in the animal's body, resulting in suffocation.

It occurs when cattle ingest cyanogenic plants. The amount of cyanide present in the plants varies depending on the plant part, season, stage of growth of the plant, whether herbicides were recently used, and environmental conditions. Drought and frost or freezing are stressful conditions that increase the risk of high levels of cyanide accumulation in affected plants. Any stressful condition that inhibits the growth of the plant can cause higher amounts of cyanide to develop. New plant growth also has higher levels of cyanide then mature plants. Leaves of cyanide-accumulating forage grasses produce 25 times more cyanide than the stems.