Articles on forages, animals, and grazing systems
Enter your E-mail to receive the monthly Grazing News Newsletter:
Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Grazing certain forages and weeds can bring the threat of prussic acid poisoning to livestock. If caution is used, this threat can be greatly reduced. Plants such as sorghum, sudangrass, sorghum-sudan hybrids, Johnsongrass, wild cherry, and others can contain cyanide-producing compounds. After a frost or during a drought it is important to use extreme caution and it is advised to keep livestock off these pastures for up to three days after a killing frost. If soils that are deficient in phosphorus and potassium are applied with high levels of nitrogen, the levels of prussic acid may increase. Leaves, new shoots, and tillers have higher levels of prussic acid.
If large amounts of prussic acid are consumed, the compound interferes with oxygen utilization and livestock can die from respiratory paralysis. Symptoms appear quickly after forage is consumed. These symptoms may include cherry red colored blood, staggering, labored breathing, spasms, foaming at the mouth, falling, thrashing, severe convulsions, and death. Immediate treatment by a veterinarian is needed to save livestock suffering from prussic acid poisoning.
When cut for hay, prussic acid content decreases significantly during the curing process. A fair amount of this poison escapes as gas during fermentation when used for silage. Although the risk decreases, it is still important to be cautious when feeding forages with possible high prussic acid content.
Using caution when grazing these forages during times of stress can usually eliminate the possibility of prussic acid poisoning in livestock. Wait the recommended time before grazing after a frost. Mixing nonthreatening forages into the diet can be beneficial as well. Using “test” animals is another option rather than turning the whole herd onto a field.
The risk of prussic acid poisoning this season can be reduced by following these practices: