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Watch for nitrates, prussic acid in hay, forages affected by drought

Cattle in drought-stricken areas of North and South Dakota and other states could be exposed to high levels of nitrates and prussic acid in forage plants and hay, according to Duane Berglund, a North Dakota State University Extension agronomist.

Crop plants known to accumulate nitrates include oats as hay, straw or stubble; corn as silage or stalks that are grazed; immature barley; wheat as pasture or hay, pearl or proso millets; flax and the sudan-sorghum complex of forages.

Forage crops know to cause prussic acid poisoning include sudangrass, forage sorghum-sudans, and sorghum varieties or hybrids and crosses. Piper sudangrass (an old variety) possesses the least of the poisoning potential when compared with the sudangrass hybrids and sorghum-sudangrass crosses, Berglund says. Forage sorghum hybrids have the greatest potential for prussic acid content and poisoning potential.

"In corn, nitrates accumulate in the lower portion of the plant when stresses reduce the crop yield to less than the supplied nitrogen fertility level," Berglund says. "Nitrates are responsible for lethal silo gas and interfere with the blood's ability to carry oxygen when fed to animals. When chopping stressed corn plants, a 12-inch stubble should be left. If it rains, allow three days before resuming chopping. Plants that recover from stress situations eventually will convert nitrates to a nontoxic form."

Prussic acid accumulates in sorghum and sundangrass that grows rapidly following stress. Poisoning occurs when animals graze young sorghum plants, drought-stunted plants or frost-damaged plants. Sorghum plants are poisonous after a frost that kills the tops, but not the crown or when new growth begins following a rain. When new shoots develop after a light frost, cattle should not be allowed to graze.

"Weeds consumed as forages under drought conditions also can be another source for nitrate poisoning," Berglund says. "Among the species that can accumulate dangerous levels of nitrates are Canada thistle, curly dock, jimsonweed, kochia, lambsquarter, various nightshades, redroot pigweed, smartweed, Russian thistle and wild sunflowers. Producers need to closely monitor livestock that may be feeding on these weeds during drought conditions."

Other drought-related resources can be found at www.ag.ndsu.edu/drought/.

Cattle in drought-stricken areas of North and South Dakota and other states could be exposed to high levels of nitrates and prussic acid in forage plants and hay, according to Duane Berglund, a North Dakota State University Extension agronomist.

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