What is Prussic Acid Poisoning?
Prussic acid is normal and can be found in all sorghums. Under normal growing conditions, prussic acid is broken down and toxic accumulations are generally avoided. However, there are certain scenarios where prussic acid can be accumulated at levels that can be toxic to livestock. Among these conditions are:
1. Poor plant growing conditions
2. Rapid growth as a result of rain or irrigation falling on previously drought-stressed fields. High concentrations of prussic acid may be found in plant leaves and regrowth less than 2 feet tall
3. Over-use of nitrogen fertilizers or presence of nutrient imbalances
4. Injury to plants caused by herbicides, frost, or hail
Hay baled early at high moisture or plants that are to be chopped and immediately fed may not have enough time to dissipate prussic acid.
How Can a Producer Prevent Prussic Acid Poisoning?
Prussic acid accumulates mainly in the leaves. Therefore, sampling for testing should be taken from the leaves. Graze standing forages only after obtaining results of safe levels of prussic acid. Producers should take precautions when allowing livestock grazing on forages that have been stressed. Among some of the precautions are:
1. Wait two weeks after irrigation or rainfall on previously drought-stressed fields and allow the plant to begin to grow before grazing
2. Defer grazing of plants that have been damaged by herbicide or frost until they are well recovered from injury
3. Do not graze grain or sorghum until plants are between 2 to 3 feet tall. If growing conditions are unfavorable, graze second-growth sorghum with caution
4. Prevent livestock from grazing plants with tillers or that appear wilted
Unlike high nitrate levels, prussic acid may dissipate from plants properly cured for hay. However, producers shouldbe cautious and should have hay tested to ensure that prussic acid levels are below 250 ppm HCN. Forage containing prussic acid should not be fed to livestock until the prussic acid level declines to a point that it can no longer be detectable.