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Managing frost-induced prussic acid risks in sorghum forage

Managing frost-induced prussic acid risks in sorghum forage


By Andi Anderson

Frost can significantly raise prussic acid levels in sorghum species, creating a risk of toxicity for livestock. Sorghum, forage sorghum, sudangrass, and their hybrids are particularly vulnerable to frost stress, which leads to the accumulation of dhurrin, a compound that breaks down into prussic acid.

If livestock graze on forage containing high prussic acid levels, it can cause muscle twitching, staggering, and even death within minutes.

To manage prussic acid risks, follow these expert guidelines from Iowa State University’s forage specialist Shelby Gruss:

1. Remove Livestock Before Frost:

When frost is forecasted, remove livestock from sorghum fields to prevent them from consuming potentially toxic forage.

2. Wait One Week After Frost:

Livestock should not graze on frosted fields for at least one week. If another frost occurs within that time, restart the seven-day waiting period.

3. Monitor for Regrowth:

After a non-killing frost, check for new growth, as young tillers often contain high dhurrin levels. Wait until the new growth reaches over 18 inches or is killed by a hard frost.

4. Safe Grazing After Killing Frost:

One week after a killing frost, prussic acid levels usually drop to safer levels, making it safer for livestock to graze. Fields densely planted with sorghum may offer protection from frost, so inspect plants carefully.

5. Feeding Alternatives:

If managing frosted sorghum is challenging, consider using silage or baleage. The fermentation process in silage reduces prussic acid content by over 50%, making it safer than grazing or hay. Haying frosted sorghum does not significantly reduce prussic acid levels, contrary to previous beliefs.

Testing for Prussic Acid:

If there is any uncertainty about the safety of sorghum forage, send samples for prussic acid testing to a lab. Proper management of frosted sorghum ensures it remains a valuable and safe forage resource for livestock.

For testing, send samples to:

Veterinary Diagnostic Laboratory

Iowa State University

1850 Christensen Drive

Ames, IA 50011

By following these guidelines, producers can prevent prussic acid toxicity and ensure the health and safety of their livestock.

Photo Credit: istock-mailson-pignata

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Categories: Iowa, Crops, Hay & Forage
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