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Prussic acid: Nightmare for cattle farmers

July 25, 2014

Fast Facts:

  • Prussic acid, high nitrate concentrations can be deadly for cattle
  • Prussic acid is common in sorghum species, if stressed
  • Drought, excessive fertilizer rates can cause prussic acid to accumulate in plants

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FAYETTEVILLE, Ark. -- High nitrate and prussic acid concentrations can be deadly for cattle, said Dirk Philipp, assistant professor for the University of Arkansas System Division of Agriculture.

Prussic acid is common in sorghum species such as forage sorghums, sorghum-sudan varieties, and Johnsongrass. Poisoning happens when cattle eat leafy growth stressed from severe conditions such as drought.

Farmers and growers should pay extra attention because these grasses attract livestock.

Don’t put hungry cattle out in a field of sorghum or Johnsongrass, he said. “Feed them hay or any other safe forage before entering the field.”

Besides drought, over-fertilization can be a big contributor to prussic acid. Even though nitrogen fertilizer can help produce high yields of sorghum forage, the lack of soil phosphorus and potassium may lead to high concentrations of prussic acid.

Cattle producers should “graze plants only after they reached 18-24 inches,” he said. “Prussic acid is mainly contained in leaves, thus low-growing leafy plants may contain dangerous levels of Prussic acid.”

Wilted plants or drought-damaged sorghums should not be grazed until at least five days have elapsed since a good amount of rain.

When cooler weather returns, growers should also be aware that frost damage can also render forages dangerous.

Philipp said that even if a sorghum forage pasture cannot be grazed, “hay can still be made as prussic acid concentrations will drop during the curing process and usually will not be toxic to animals.”

For more information about forages, visit or contact your county extension office.

The University of Arkansas System Division of Agriculture offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.

By Kezia Nanda
For the Cooperative Extension Service
U of A System Division of Agriculture

Media Contact: Mary Hightower
Dir. of Communication Services
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2126

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