Cyanide toxicity is relatively common in horses due to the large number of cyanogenic forage plants such as sorghum, sudan grasses and corn. The amount of cyanide present in these plants are highly variable, but are typically highest during the spring while blooming. Drought and dry growing conditions enhance the accumulation of cyanogenic glycosides in many of these plants as well.

Once ingested, the toxin is quickly absorbed from the horse's gastrointestinal tract, and into the bloodstream. Once in the blood, it travels all over the body and inhibits blood cells from delivering oxygen to tissue cells. The blood becomes supersaturated with oxygen and appears bright red. Cyanide essentially inhibits the use of oxygen by the cells in the horse's body, causing them to eventually suffocate to death.

Plants capable of producing high levels of cyanide:

• Apricot
• Arrowgrass
• Cherry trees
• Bitter almond
• Elderberry
• Johnsongrass
• Peach
• Sudangrass
• White clover

An increase in toxicity in plants containing cyanogenic glycosides can be caused by a number of factors which include:

• Stage of plant growth: Generally, cyanide toxin levels are highest when the plant is young and/or rapidly growing.
• Plant part: Certain plant parts tend to accumulate higher cyanide levels than others. For example, the leaves of cyanide-accumulating forage grasses were found to produce 25 times more cyanide than the stems.
• Wet leaves, such as from dew or rain
• Environmental stresses: Such as drought, frost, hail, and flooding.
• A high nitrogen to phosphorus ratio in the soil
• Herbicides can increase both the toxicity and the palatability of the plants

Any stressful condition that inhibits the growth of the plant can cause higher amounts of cyanide to develop.

Symptoms of Cyanide toxicity

Symptoms of acute poisoning usually occur within ten minutes of ingestion. Most common clinical signs include:

• Initial excitability with muscle tremors
• Salivation
• Labored breathing
• Muscular incoordination
• Gasping
• Convulsions