Frost: Prussic Acid Concerns

prussicacidGrazing forages during the summer months is a great way to reduce stored feed costs. However, there are some risks that come with grazing certain forages and weeds. It is important to be cautious this summer to reduce the risk for prussic acid poisoning, as prussic acid poisoning tends to be worse during times of drought.

Prussic acid poisoning occurs when plants such as sorghum, sudangrass, sorghum-sudan hybrids, Johnsongrass, wild cherry, and others contain cyanide-producing compounds. Wild cherry and Johnsongrass have much more risk than the other forage species listed above. If large amounts of these forages are consumed, especially after frost or during severe drought, then prussic acid (cyanide) is produced and interferes with oxygen utilization and livestock can die from respiratory paralysis. Symptoms appear quickly after the forage is consumed. These symptoms may include cherry red colored blood, staggering, labored breathing, spasms, foaming at the mouth, falling, thrashing, severe convulsions, and death. If an animal is seen showing these symptoms, seek immediate treatment for these animals by a veterinarian.

To reduce the risk of prussic acid poisoning, consider some of the following management tools:

  • Incorporate forages that do not produce prussic acid into the diet to dilute the concentration of prussic acid.
  • Avoid applying high levels of nitrogen to soils deficient in phosphorus and potassium, as this may cause levels of prussic acid to increase .The amount of nitrogen added should be determined by using a soil test.
  • Contact your local county extension agent and inquire about getting your forages tested before placing cattle on these fields.
  • Use “test” animals if you have not had high risk forages tested, rather than
  • turning the whole herd onto a new field.
  • Cut high risk forages for hay, as prussic acid content decreases significantly during the curing process.
  • A fair amount of prussic acid also escapes as a gas during fermentation when used for silage. However, be sure to delay feeding silage for six to eight weeks following ensiling.
  • Although these practices may reduce the risk of prussic acid poisoning, it is still important to be cautious when feeding forages with possible high prussic acid content.

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