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Morning Sun
  • EXTENSION CONNECTION: Nitrates and Prussic Acid in forages

  • Rightfully so there are concerns when utilizing johnsongrass and related forage species such as sudangrass and sorghums as forage sources, particularly during years when moisture is short. Nitrates and prussic acid both have the potential to be present in toxic amount in these forages.

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  • Rightfully so there are concerns when utilizing johnsongrass and related forage species such as sudangrass and sorghums as forage sources, particularly during years when moisture is short. Nitrates and prussic acid both have the potential to be present in toxic amount in these forages.
    Nitrates can be a problem in as corn, sorghum, canola, cereal grains, and some grasses during exposure to drought. More nitrate is taken up by the plant than is used because of poor growing conditions, resulting in a potentially toxic accumulation of nitrates in the lower portion of affected plants. The metabolism of high nitrate feedstuffs interferes with the blood of affected animals to carry oxygen, causing asphyxiation.
    Management practices to avoid problems with nitrates include 1) Waiting for a period of good growing conditions to allow nitrate levels to return to safe levels prior to grazing. 2) Ensiling the crop reduces nitrate levels about 50%. 3) Raising cutting height to leave highest nitrate part of plant in field. 4) Grazing animals select lower nitrate leaves and stems instead of higher nitrate lower stems if adequate forage is available. 5) High nitrate feeds can be diluted with lower nitrate forages and grains.
    Forage tests should be submitted on feeds with the potential for high nitrates to determine the nitrate level as well as nutrient content of the forage. If the nitrate level is known rations can be formulated to safely feed theses forages. Contact the Altamont office at (620) 784-5337 for information about conducting forage tests.
    Prussic acid poisoning is caused by cyanide production in forage sorghums, grain sorghums, sudangrass and johnsongrass. Prussic acid poisoning is most commonly associated with regrowth following a drought-ending rain or the first autumn frost. New growth from frosted or drought-stressed plants is palatable but can be dangerously high in cyanide.
    Once eaten, cyanide is absorbed directly into the bloodstream and binds to enzymes in the cell, preventing blood hemoglobin from transferring oxygen to cells and the animal dies from asphyxiation. Prussic acid acts rapidly, often killing the animal within minutes.
    Because it occurs quickly, the symptoms are usually observed too late for effective treatment.
    In the absence of a veterinarian, and if there is little doubt about the diagnosis, the animal can be treated with an injection of sodium nitrate and sodium thiosulfate. Animals still alive one to two hours after the onset of visible signs usually recover.
    Young, rapidly growing plants are likely to contain high levels of prussic acid. Cyanide is more concentrated in the growing point and young leaves than in older leaves or stems. New sorghum growth, especially “suckers” or tillers, following drought or frost are dangerously high in cyanide. Generally, any stress condition that retards normal plant growth may increase prussic acid content. Wait until regrowth get fifteen inches or taller after a drought ending rain before beginning grazing. After a killing frost, wait at least four days before grazing to allow the released HCN gas to dissipate.  
    Page 2 of 2 - Prussic acid does not remain in properly cured harvested forage so there is no risk from prussic acid when feeding properly cured hay.
    For more information about this or other livestock topics please contact livestock agent Keith Martin at (620) 784-5337 or you can email rkmartin@ksu.edu. Or you can contact Scott Gordon at the Independence office at (620) 331-2690.
    We also offer programs in Family Consumer Science, 4-H & Youth, as well as horticulture. Upcoming program information as well as contacts for specific concerns can be found at our website http://www.wildcatdistrict.ksu.edu or you can follow us on twitter at https://twitter.com/Wildcat_Ext or like us on facebook at http://www.facebook.com/Wildcat.Extension.District
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