Prussic acid poisoning can be a concern when grazing sorghum species like sorghum-sudangrass, grain sorghum stubble and weeds such as shattercane and Johnson grass. Wild cherry tree leaves also contain prussic acid when wilted. Poisoning can occur when ruminant animals consume plants containing cyanide-producing compounds. These compounds interfere with the blood’s ability to carry and transfer oxygen. They are released when the cells of plant leaves are damaged from cutting or freezing. Prussic acids will dissipate over time, unlike nitrates which can be a problem during times of drought.
Initial prussic acid poisoning symptoms are similar to cyanide poisoning: deep, rapid breathing and excessive foaming from the nose and mouth occur within a few minutes of consumption, followed by depression and severe difficulty breathing. Death generally occurs within a few hours of ingestion.
New growth and young shoots have higher prussic acid levels. Do not graze forage less than 18 inches tall. Do not allow the animals to graze overnight if frost is forecast. After a non-killing frost, wait two weeks before grazing to allow the levels to drop. After a killing freeze, wait for the plant material to dry completely, usually three to five days. If the potential exists for prussic acid poisoning, provide the animals with dry hay prior to turning them out to graze.
If feeding forage type sorghums as green chop, feed immediately after chopping. Do not allow the material to sit for an extended period of time. The cyanide-producing compounds generally dissipate when the plants are allowed to dry and baled or when they are made into silage or baleage. But, if the levels were potentially high when harvested, test the forage before feeding.
For more information, contact Valerie Tate, agronomy specialist for MU Extension at
firstname.lastname@example.org or call 660-895-5123. University of Missouri Extension programs are open to the public.
Valerie Tate is a field specialist in agronomy for the University of Missouri Extension.