Cyanide (also referred to as prussic acid and hydrocyanic acid) is a highly potent, rapidly acting poison. Several common plants have the capability of accumulating large quantities of cyanogenic glycosides, which are found in the epidermal cells (outer tissue) of the plant. These plants also contain certain enzymes within the mesophyll cells (inner tissue) that upon rupture, mix with cyanogenic glycosides, produce cyanide. These plant cells are ruptured by wilting, drought, crushing, chewing, chopping, trampling, freezing, and cutting into the plant.
Upon ingestion of plant parts containing varying levels of cyanide, the toxin rapidly enters the cow's blood stream where it is transported throughout the body of the cow. Cyanide inhibits the use of oxygen by the cells in the body, resulting in suffocation.
Plants capable of producing high levels of cyanide:
The amount of cyanide found in these 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.
A 400kg (880 lb) cow would only have to consume 1 kg (2.2 lb) of fresh leaves from the Choke cherry (Prunus virginiana
) tree to ingest lethal amounts of cyanide. The lethal dose of HCN for cows is 2.0 mg/kg of body weight.