Cyanide poisoning, more commonly referred to as prussic acid poisoning, can have a very abrupt and deadly effect on ruminant livestock grazing forages and requires careful management as frosts and freezes begin in the area. Plants, such as sorghum, sudangrass, sorghum-sudan hybrids, Johnsongrass, wild cherry, and others, contain compounds that produce free cyanide when these plants are damaged by frost or drought conditions. Grazing these plants when they are producing young shoots (less than 18 to 24 inches tall) also increases the risk. Using caution when grazing these forages during times of stress can usually eliminate the possibility of cyanide poisoning in livestock. Wait the recommended time before grazing after a frost. Waiting for two weeks after a light frost (temperature greater than 28°F) is recommended. For a killing frost, wait until the material is completely dry and brown (usually the toxin dissipates within 72 hours). Grazing at night when a frost is likely is not recommended as high levels of toxins are produced within hours after frost occurs. Delay feeding silage for six to eight weeks following ensiling of forages in the sorghum family to allow the toxic compound to dissipate. If cut for hay, allow to dry completely so the cyanide will volatilize prior to baling. The toxicity can be retained in cool or moist weather, so allow slow and thorough drying. For more information, follow this link to the UK publication “Cyanide Poisoning in Ruminants”:

Cyanide poisoning hazards after frost or freeze