Prussic acid poisoning can cause problems in cattle that consume sudangrass, sorghum-sudangrass hybrids or forage sorghums, warns Mike McFadden, Michigan State University Extension educator.

Of the three types of forage, forage sorghums have the highest potential for prussic acid poisoning and sudangrasses have the lowest, he says. These species contain cyanogenic glucosides, which can be converted into prussic acid in the plant. Under normal growing conditions, the cyanogenic glucosides and the enzyme responsible for converting them to prussic acid are located in separate areas of the plant.

Conditions that cause plant cells to rupture can allow the enzymes to convert the glucosides into prussic acid. Drought, freezing, cutting, chopping, chewing and maturity can contribute to plant cell rupture. The highest potential for poisoning occurs when animals consume plant regrowth following a frost or drought.

Prussic acid enters the bloodstream after being absorbed through the rumen. In the bloodstream, it binds to hemoglobin, which inhibits oxygen transfer and causes asphyxiation and possible death. Symptoms of prussic acid poisoning include increased salivation, difficult breathing, excitement, staggering, convulsions and collapse. The mucous membranes around the eyes and gums may be bright pink or blue and the blood will be a bright red color. Death may be rapid in some cases but immediate veterinary intervention can also save other animals.

McFadden lists several practices that reduce the risk of prussic acid poisoning:

  1. Do not greenchop or graze these forage species when they’re less than 18-24” tall.
  2. Do not allow hungry cattle to graze forages that may contain prussic acid. Feed grain or other forage before allowing grazing access.
  3. Do not graze at night when frost is anticipated.
  4. Wait two weeks after a killing frost to graze.
  5. Allow chopped forage to ferment for six to eight weeks before feeding.
  6. Do not graze during droughts or for at least one week after a rain event following drought.
  7. Have suspect forages analyzed for prussic acid content.

You can find more information about prussic acid poisoning here.