By Andi Anderson
Fall frosts can create significant challenges for livestock producers who rely on sorghum-based forages. Agricultural experts advise farmers to carefully monitor grazing conditions because frost-damaged sorghum plants may develop elevated levels of prussic acid, a compound that can be harmful to animals.
Prussic acid is a cyanide-containing substance that forms from a naturally occurring plant compound called dhurrin. Sorghum-family plants use dhurrin as part of their natural defense system. When frost damages plant cells, chemical reactions can convert dhurrin into prussic acid. If livestock consume forage containing high concentrations of this compound, oxygen transfer within the body can be disrupted, potentially leading to serious health concerns.
Most plants in the sorghum family can produce prussic acid unless they have been specifically bred to be dhurrin-free. Common sorghum species, sorghum-sudangrass hybrids, Johnsongrass, and shattercane are among the plants that may present a risk following frost events. While Johnsongrass generally contains lower levels than some other sorghum types, caution is still recommended.
Agricultural specialists note that the greatest risk usually occurs during the week following a frost. Prussic acid concentrations are often highest near the base of the plant. To reduce risks, livestock should not graze sorghum-based crops until plants have recovered and regrown for at least one week after frost. Producers are also encouraged to avoid grazing sorghum plants shorter than 18 inches in height.
Stored forage generally presents a lower risk than direct grazing. Ensiling forage can significantly reduce dhurrin levels and is often considered one of the most effective management options for minimizing prussic acid concerns. This makes silage a preferred feeding option for many livestock producers using sorghum crops.
Recent research suggests that drying forage into hay may not completely eliminate risk. Although prussic acid can decline during storage, some dhurrin may remain and later be converted into cyanide-containing compounds during digestion. As a result, forage testing and careful management remain important.
Farmers should watch livestock closely for symptoms such as shortness of breath, difficulty walking, staggering, or other signs of oxygen deficiency. Forage testing kits and laboratory analysis can help assess risk levels, although conditions may continue to change for several days after a frost event.
Despite these challenges, sorghum species remain valuable forage crops because of their strong establishment, drought tolerance, and efficient water use. When proper grazing guidelines and management practices are followed, sorghum forages can continue to provide a safe and reliable feed source while helping producers maintain productive livestock operations.
Photo Credit: istock-mailson-pignata
Categories: Ohio, Livestock