During drought nitrates and prussic acid can build up in forages to levels dangerous to livestock, causing severe illness and even death after eating affected forages, says University of Missouri Extension agronomist Jamie Gundel.

Nitrates tend to concentrate in the bottom third of the plant. It shows in the plant's stem and stalks more than leaves, Gundel says.

Plants most susceptible to nitrate buildup include sorghum, Sudan grass, sorghum-Sudan grass hybrids, corn, millet and perennial grasses. Some weeds can also accumulate nitrates, including curly dock, jimsonweed, Johnson grass, kochia, lambsquarter, nightshades, pigweed, Canada thistle and smartweed.

Poisoning symptoms include labored breathing, muscle tremors, weakness, lack of coordination, diarrhea, frequent urination and dark red blood. Death usually occurs within four hours of consumption.

Gundel suggests the following to reduce nitrate levels in forages:

During drought, prussic acids also can cause high cyanide levels in stressed leaves of young plants of Johnson grass and some sorghum lines. Pearl millet is unaffected.

Prussic acid poisoning symptoms include accelerated breathing, foaming of the mouth and nose, involuntary urination, depression, inability to stand, muscle tremors and bright red blood. Death can happen within 15 minutes.

Prussic acid concentrates in the new growth of plants, especially after drought, frost or herbicide damage. Levels drop over time and are not a problem in properly cured hay, says Gundel.

To avoid prussic acid poisoning, Gundel suggests the following:

More information on forages is available from the Alliance for Grassland Renewal. The alliance includes partners from university, government, industry and nonprofit groups.

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