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Beware of Nitrate Poisoning in Livestock

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Dry, drought-stressed corn plants exhibit curling and dead leaves with no ear production.
Photo Credit:
Karl Hoppe, NDSU
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Cattle feed produced during a drought may have higher levels of nitrate than would be safe for cattle consumption. Ruminant animals, such as cattle and sheep, are susceptible to nitrate poisoning because of their digestive process. In the rumen, nitrate is converted to nitrite, and when nitrite moves into the blood stream it prevents hemoglobin in red blood cells from carrying oxygen, resulting in suffocation. Also, abortions can occur in cows where lower levels of nitrates are fed. The same reaction takes place in horses' hindgut; however, the reaction occurs to a much lesser extent, thus nitrate poisoning is very rare in horses.

Feeding drought-stressed forages from oats, barley and corn causes the majority of nitrate poisoning cases in North Dakota. However, a number of other plants also can accumulate nitrate, including wheat, sudangrass, sorghum-sudan hybrids, turnips and pearl millet. If producers are considering using low-yielding crops as livestock forage, they should be tested for nitrates prior to feeding.

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TESTING FOR NITRATES

Testing for nitrates should be done before fields are grazed or before harvested feeds are fed. Sample both lowland green areas and highland dry areas. A larger number of samples will provide a more accurate indication of what can be grazed safely. Leaves contain less nitrate than stalks or stems, while the seed and flower usually contain little or no nitrate. When grazing a corn field, check for nitrate concentrations in the leaves separately from the stalks. Cattle will graze the leaves before grazing the stalk. The lower parts of the corn stalk will have the highest concentration of nitrates. Plant parts closest to the ground contain the highest concentrations of nitrates. Thus, the risk of poisoning can be reduced when haying by raising the cutter bar above 6 inches or by monitoring grazing livestock and removing them when the stubble height of the plants is at 6 inches.

Several labs test for nitrates in plants.  Soil testing labs (e.g. AGVISE), veterinary diagnostic labs (e.g. NDSU Veterinary Diagnostic Lab) and feed testing labs (e.g. Stearns DHIA Lab, Dairyland Labs) will do nitrate-nitrogen testing for toxicity on plant tissue or hay/feed samples.  Test cost is $12-18 per sample. Samples should be packaged in a clean plastic bag and shipped to a laboratory.

FEEDING HIGH-NITRATE FORAGES

Nitrate levels will remain constant in stored hay. However, nitrate levels can be reduced by 30-50% during the ensiling process as microbes metabolize the nitrates during good fermentation conditions. When ensiling is too wet (greater than 70% moisture), poor fermentation will result and nitrates may not be metabolized.

High-nitrate hay must be blended with low-nitrate feeds.  Blending feeds is best accomplished with a total mixed ration (TMR) and a mixer wagon. Hay grinding is also an option when grinding high and low concentration nitrate hays together in the proper proportions. Don’t use hay rings and expect cattle to blend the hays on their own. That might be a deadly mistake. Also, do not overstock pastures when grazing high-nitrate forages. Overstocking increases the amount of high-nitrate plant parts (stems and stalks) that are consumed by livestock.

For more information see Nitrate Poisoning of Livestock.

Karl Hoppe, Ph. D.
Karl.Hoppe@ndsu.edu
Extension Livestock Specialist

Miranda Meehan
Miranda.Meehan@ndsu.edu
Livestock Environmental Stewardship Specialist