Prussic Acid Poisioning

DISORDER: Prussic Acid
Plant Species: Primarily occurs in sorghums commonly less than 1½ foot. (johnsongrass, grain sorghum, sorghum-sudan), wild cherry, and occasionally on white clover and birdsfoot trefoil.Does not occur in pearl millet or corn.
Conditions: Poisoning is associated with consumption of plant parts with high levels of prussic acid (HCN), by a cyanogenic compound that is highly poisoning. Prussic acid is associated with rapidly growing plants. Occurs in young plant tissue that is damaged or stressed, (for example: after a frost or drought after heavy N fertilization) or mechanically injured (after 4 wheelers or ATVs are run over a field). Under these conditions the cells are ruptured mixing their enzyme content with that of Dhurrin (a cyanogenic glycride in sorghums), breaking down dhurria to prussic acid.
Causes: Plant HCN levels greater than 50 ppm dry mater basis or 200 ppm on wet basis.
Mode of Action: Cyanogenic glucosides are converted by enzymatic hydrolysis to HCN (Hydrogen cyanide).HCN causes acute respiratory inhibition by inhibiting the enzyme cytochrome oxidase.
Animal Symptoms: Labor breathing if detected early enough. May occur minutes (10-15 min) after consumption of feed.
Treatment: Treat with sodium thiosulfate or methylene blue to detoxify CN.
Prevention: If plants have been injured defer grazing until they are recovered from injury. After a hard freeze, or severe drought, avoid grazing for approximately 1 week. After a rain or irrigation on drought stressed fields wait at least 2 weeks after plants begin to grow before grazing.
Notes: Due to volatilization of CN compounds, hay can be fed; however, you still need to monitor forage by taking samples and have them tested to confirm ‘safety’ in feeding the hay. Forage samples can be sent to:

  • Texas Veterinary Diagnostic Medical Laboratory (TVMDL) to determine toxic levels for a fee of $15.00 in-state and $20.00 out-of-state samples.
    Phone: (979)845.3414 or 1.888.646.5623,  Fax: (979)845.1794
    P.O. Drawer 3040, College Station, TX 77841-3040

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