Livestock and Prussic Acid Poisoning

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We will soon have our first frost of the year. Many producers become concerned about grazing forages that have the potential to cause prussic acid poisoning and what they can do to minimize the risk.

Prussic acid, or cyanide, can build up to dangerous levels following a frost, after a drought, or anytime the plant is stressed. Prussic acid hinders the oxygen-transferring ability of the red blood cells, which causes animals to suffocate. Ruminant animals such as cattle, sheep, and goats are more susceptible than non-ruminant animals like pigs. The main grasses that pose a problem are sorghums, sorghum-sudangrass crosses, and sudangrass. Other plants that may contribute can include but are not limited to Johnson grass, arrowgrass, and cherry trees. Plant parts that are especially high in prussic acid include the leaves and young or new growth.

Allowing the plants to rest after frost reduces the risk of poisoning because it allows the cyanide levels to decrease. Once a frost occurs, take your animals off the pasture and prevent grazing of the sorghum, sorghum-sudangrass, or sudangrass. Sufficient drying and recovery should occur within 7-10 days following the frost; after that it is probably safe to return your animals to that field. I always err on the side of caution and tell producers to wait a full 10 days before turning their animals back onto pasture.

Here are some other tips for handling and/or preventing possible prussic acid poisoning in livestock:

  • Do not graze sheep on sudangrass or hybrids until it is 12-15 inches tall.
  • Do not graze cattle on sudangrass or hybrids until it is 18-24 inches tall.
  • Sorghum may not be safe to graze until fully headed.
  • Have the plants tested for toxicity levels before grazing.
  • Do not graze hungry livestock on sorghum or sorghum-sudangrass hybrids. Potential for poisoning is increased with the amount of this high-risk forage that is consumed.
  • Select grass varieties that are low in prussic acid.

What should you do if you think your animals may be suffering from prussic acid poisoning? Call your local vet and remove them from the pasture. Don’t delay — time is of the essence with any poisoning! Check your pastures for the cause of the problem to avoid your other animals getting sick. Avoid plants that can cause prussic acid poisoning and monitor animals.

If you are interested in learning more about beef cattle or starting a beef cattle farm, please attend our Beef Cattle 101 series for beginners or new farmers. The two-class series will be held on November 14 and 21, 2019, with a farm visit on November 23. The cost for the class is $25 (paid by check or money order only, made payable to Robeson County Cooperative Extension), and registration is due by November 7. For more information, or to register, please contact Taylor Chavis, Extension Livestock Agent, at 910-671-3276, by email at, or visit our website.

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