Prussic Acid (Hydrogen Cyanide) Toxicity
Prussic acid, also known as hydrogen cyanide (HCN), can accumulate in certain forages under stress conditions such as frost, drought, or rapid regrowth. HCN concentrations exceeding 500 ppm (dry matter basis) are considered highly dangerous for livestock.
Key Risk Considerations
- Do not allow hungry cattle to graze forages known or suspected to contain high prussic acid levels.
- High-risk crops include:
- Sorghum
- Sorghum–sudan hybrids
- Flax
- Some varieties of birdsfoot trefoil
- Native species such as arrowgrass and chokecherry leaves
Ensiling and Toxicity Reduction
- Ensiling can reduce prussic acid levels—and nitrates—by up to 50%.
- However, if initial HCN concentrations are extremely high, even ensiling may not reduce levels enough to ensure safe feeding.
- Always test suspect forages before feeding or grazing.
Safety Recommendation
Test all feeds that may contain prussic acid to determine actual HCN concentration and ensure appropriate management decisions.
Management
- Avoid grazing regrowth until new shoots reach ≥2 feet.
- Thorough curing reduces risk substantially.
- Horses and pigs are less susceptible than cattle.
Symptoms
- Nervousness, rapid breathing, staggering
- Convulsions, respiratory failure
- Death may occur within 30–45 minutes
- Does not accumulate in the body—animals recover once removed from the source