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Learn the risks of prussic acid poisoning

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By David Harrison

Producers should be aware of the risk of cyanide or prussic poisoning in cattle, goats, and other ruminants.

Sudangrass, johnsongrass, sorghums and sorghum-sudangrass hybrids contain cyanogenic glycosides. When the plant undergoes a stressful event such as cutting, wilting, freezing and drought, the plant cells rupture which allows the cyanogenic compounds to produce poisonous cyanide.

Ruminants can also convert the cyanogenic compounds in the plant into cyanide.  The toxic gas goes to the bloodstream and blocks the release of oxygen from red blood cells. The animal dies from lack of oxygen.  

Clinical signs of cyanide poisoning can occur within minutes to hours after consuming the toxic forage. Usually the affected animals are found dead but, if observed early, may show rapid, difficult breathing, frothing at the mouth, muscle tremors, staggering and then collapse.

It is important to recognize and avoid dangerous situations. Ruminants should only graze susceptible plants that are at least 18-24 inches tall. Do not graze plants with young tillers. Do not graze plants during drought periods when growth is severely reduced or the plant is wilted or twisted and wait at least one week after rainfall to resume grazing.

Do not graze at night when frost is likely. Frost allows conversion to hydrogen cyanide within the plant. Do not graze for two weeks after a non-killing (more than 28 degrees) frost. It is best not to allow grazing after a light frost as this is an extremely dangerous time. It may be several weeks before the cyanide potential subsides. Do not graze after a killing frost until plant material is completely dry and brown.  

If high cyanide is suspected, do not graze or feed as green chop. If cut for hay, allow at least 72 hours or longer before baling. Allow thorough drying because toxicity can be retained in cool or moist weather. Delay feeding as silage 6 to 8 weeks.