Don't Risk Prussic Acid Poisoning

Oct 23, 2020

Tara Jo Bina
Countryside Feed Sales and Nutrition Specialist

With the first hard freeze rapidly approaching, its time think about the risk of prussic acid poisoning. A basic understanding of what happens to the plant after a hard freeze and how it impacts animals can help prevent losses this fall.

What is Prussic Acid Poisoning?
Prussic acid, also known as hydrocyanic acid or cyanide, is a lethal toxin produced by drought or frost damaged plants, such as sorghums and sudangrasses. The stress of a killing frost, or other events that cause wilting, trigger enzymes to release prussic acid. Enzymes produced by ruminal microbes also cause release of the toxin into an animal’s digestive system, making ruminant animals more susceptible to prussic acid poisoning.
As mentioned before, Cyanide is a lethal toxin. Once it is released into an animal’s digestive system, it is absorbed, and prevents cells from utilizing oxygen properly, ultimately causing an animal dye of suffocation. Some symptoms of prussic acid poisoning include muscle spasms, rapid respiration rates, purple colored mucous membranes, excessive salivation, and death.

What plants are dangerous?
Plants categorized as sorghums or sudangrasses are the most common plants in our region that produce prussic acid. The highest concentrations of the toxin are found in leafy material, especially of young, rapidly growing plants. Unfortunately, this portion of the plant is what cattle prefer to graze, making safely grazing frost damaged sorghum sudan nearly impossible.

Are there treatments?
Because of the rapid progression of prussic acid poisoning, effective treatment poisoning is very difficult. Death can occur within 10 to 15 minutes of consuming toxic forages.

How do you prevent it?
Since treatment is unreliable, prevention is the best potion for prussic acid poisoning.

One of the best ways to avoid this problem is to prevent animals from consuming toxic plants. Removing cattle from sorghum sudan pastures before a killing frost is very effective. Since prussic acid dissipates as wilted plant tissues dry out, animals can safely return to grazing these pastures about a week after a killing frost. Turning cows out full and not hungry is also recommended on these pastures.

Monitoring regrowth after cattle return to grazing is also important. Since the leafy material of rapidly growing plants contains the highest concentrations of the toxin, regrowth can pose a problem in fall grazing when plants are under frost conditions frequently. One way to manage this potential issue is to heavily stock the pasture so that animals can’t selectively graze. Consuming the risky leaf material as well as the fairly safe stalks greatly reduces the risk of prussic acid poisoning after a hard freeze.

Keep an eye on the forecast for the first hard freeze, pull cows off of sorghum sudan pastures, don’t risk prussic acid poisoning! Contact your Countryside Feed representative with any questions or concerns about prussic acid poisoning!

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