Six Plants That Can Cause Livestock Poisoning

By Scout Nelson

Prussic acid is a natural plant defense that can create serious health risks for livestock. Although it is most commonly linked to sorghum and sudangrass, several other plants found across the Northern Great Plains can also produce this toxic compound.

Farmers and livestock producers need to recognize these plants, especially when grazing areas experience drought, frost, mowing, or other conditions that damage plant tissue.

This information is highlighted by Parker Witt, SDSU Extension Crop-Livestock Systems Field Specialist, and Pete Bauman of SDSU Extension. Their work explained the risks associated with prussic acid and identifies several plant species that producers should watch for in pastures, rangelands and hay.

Understanding Prussic Acid

Prussic acid is the common agricultural name for hydrogen cyanide (HCN), a toxic substance released through a chemical reaction inside certain plants. These plants contain natural compounds called cyanogenic compounds, which remain separate from the enzymes that help release HCN.

When plant cells are damaged by freezing, wilting, trampling, grazing, chopping, or mowing, these compounds mix with enzymes and produce HCN. This process can be compared to breaking a glow stick. The chemicals remain separate until the outer barrier breaks, allowing them to mix and create a reaction.

Once released, HCN gradually escapes into the air. However, the original cyanogenic compounds can remain in living or harvested plant material. Microorganisms in the rumen can also release HCN during digestion. Therefore, drying forage or waiting for some time does not always make it safe.

Laboratory testing for total HCN potential is the most reliable way to check questionable forage before feeding or grazing.

Plants That Can Produce Prussic Acid

Several plants found in South Dakota can produce prussic acid. Their toxicity levels and exposure risks vary.

Johnsongrass

Johnsongrass (Sorghum halepense) is a warm-season perennial weed that spreads through seeds and underground roots called rhizomes. It commonly grows along roadsides, field edges, drainage areas, and disturbed land.

Like cultivated sorghum, Johnsongrass contains dhurrin, a compound that can release HCN. Young plants and fresh growth following drought, mowing, grazing, or frost can create higher risks.

Cattle, sheep and goats are all vulnerable. Hungry animals may consume large amounts of young leaves quickly. Producers should avoid grazing frost-damaged Johnsongrass and wait at least seven days after a complete killing freeze before allowing livestock to graze standing forage.

Arrowgrass

Saltmarsh arrowgrass (Triglochin maritima) and marsh arrowgrass (Triglochin palustris) are perennial plants found in wetlands, wet meadows, stream edges and salty or alkaline soils.

These grasslike plants have narrow, fleshy leaves and small flowers or fruits growing along slender stalks. They contain cyanogenic compounds called taxiphyllin and triglochinin, which can release HCN when plant tissue is damaged.

Drought, frost, and cutting can increase the risk. Cattle and sheep are common animals exposed while grazing wet meadows or eating contaminated hay. Producers should consider forage testing when arrowgrass grows in large amounts or experiences stress.

Reed Canarygrass

Reed canarygrass (Phalaris arundinacea) is a tall, cool-season perennial that grows near wetlands, streams and low-lying areas. It can form thick stands and provide green forage during early spring and late fall.

Prussic acid production in this plant is not fully understood. SDSU Extension research has detected HCN in frost-exposed reed canarygrass, although the levels were below those normally linked to acute poisoning.

The plant is also associated with tryptamine alkaloids, which can cause neurological problems known as Phalaris staggers. When livestock becomes sick, testing should consider HCN, alkaloids, nitrates, water quality and other possible causes.

Flax

Cultivated flax (Linum usitatissimum) contains several cyanogenic compounds that can release HCN. Livestock may face exposure when grazing young, drought-stressed or frost-damaged flax.

Failed crops, volunteer flax, screenings, and flax-processing products can also create feeding risks. Ruminants, including cattle, sheep and goats, are especially vulnerable because rumen microorganisms can release HCN during digestion.

Producers considering failed flax crops for emergency livestock feed should have the material tested before feeding.

Cherry Species

Chokecherry (Prunus virginiana) is common in South Dakota, especially in shelterbelts, wooded areas, creek corridors, and brushy pastures. Other species, including wild black cherry, pin cherry and American plum, can also contain cyanogenic compounds.

These plants contain substances such as prunasin and amygdalin. Young leaves and shoots may have high cyanogenic potential, while wilted leaves create a major livestock concern.

Frost, drought, pruning, herbicide damage, and storms can cause leaves and branches to wilt. Cattle may consume fallen branches, while goats and sheep can face greater exposure because they naturally browse shrubs. Producers should remove cut and fallen cherry branches from livestock areas.

Serviceberry

Serviceberry (Amelanchier alnifolia) is a native shrub found mainly in western South Dakota, including the Black Hills, wooded draws and stream areas.

Its leaves and young shoots contain cyanogenic compounds that can release HCN after frost, wilting, or physical damage. Although reported livestock poisoning cases are less common than those linked to chokecherry, exposure remains possible.

Cattle may consume broken branches in pastures, while goats and sheep may browse the living shrubs. Risk increases when alternative forage is limited.

Protecting Livestock from Prussic Acid Poisoning

Prussic acid risks are not limited to sorghum and sudangrass. Several common pasture plants can produce HCN when their tissues are damaged.

Farmers should regularly inspect grazing areas, identify potentially toxic plants, and avoid allowing hungry animals to graze stressed or damaged vegetation. Fallen branches and questionable forage should be removed or tested before feeding.

Drying and waiting may reduce free HCN, but they do not guarantee safe forage. Laboratory testing for total HCN potential remains an important step when plant safety is uncertain.

Understanding these plant risks and taking proper precautions can help livestock producers prevent poisoning, protect animal health, and maintain safer grazing systems.

Photo Credit: pexels-jeffrey-czum