Corn growth is slow and conditions are “right” this season for the production of toxic nitrate levels in salvaged corn silage, says J.W. Schroeder, North Dakota State University Extension Service dairy specialist.

That can lead to poisoned cattle and abortions as well as production of silo gases that can be lethal to animals and humans, he adds.

Some producers may not have to worry about the problem. They likely used nominal rates of nitrogen fertilizer and have experienced continuous drought since its onset in mid-May, Schroder says. Those who use manure and have had intermittent showers producing more forage growth but little or no grain should be cautious about salvaging corn as silage.

“In particular, growers should be very cautious about salvaging corn as green chop or silage feed immediately after it is cut,” Schroeder says. “Ensiling corn that is suspected of having high nitrate levels is preferred to green chopping because the fermentation process will decrease nitrate levels by about 50%.”

Anyone who green chops or applies manure should send in silage samples for nitrate testing before feeding the material to livestock. Silages with less than 1,000 parts per million (ppm) of nitrate are safe to feed.

“Even forage with levels in excess of 1,000 ppm of nitrate-N can be fed if diluted with other feedstuffs, but it is important to know what you have before you feed it,” the dairy scientist says.

Plant samples need to be representative of the field or bales in question. They should be packaged in clean plastic bags and shipped to a laboratory for analysis.

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Producers should also watch livestock for nitrate-poisoning symptoms, including labored breathing, loss of weight and lack of appetite. Acute poisoning can occur a half-hour to four hours after animals consume toxic levels of nitrate.

Pregnant livestock that survive nitrate poisoning may abort because of a lack of oxygen to the fetus. Abortions generally occur 10-14 days after exposure to nitrates.

Silo gas is another problem with nitrate accumulation in drought-stressed corn. The gas is common in all silages but more so in forage crops such as corn and sorghum. Nitrates combined with organic silage acid to form nitrous oxide produce a silo gas heavier than air and very lethal to humans and livestock.

The North Dakota Veterinary Diagnostic Laboratory will test for nitrates. But first contact the lab at 701-231-7527 or 701-231-8307 and send a fax at 701-231-7514. Visit for a fee schedule and information on preparing a sample. Send samples to NDSU, Dept. 7691, P.O. Box 6050, Fargo, ND 58108-6050.

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