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Published September 16, 2013, 10:19 AM

Nitrates in corn silage pose risk

This year’s weather conditions could lead to the development of nitrates in corn silage.

By: NDSU Extension Service,

This year’s weather conditions could lead to the development of nitrates in corn silage.

High levels of nitrates in corn silage can be toxic to animals and humans, says North Dakota State University Extension Service dairy specialist J.W. Schroeder.

Nitrates can accumulate in corn during unfavorable conditions when growth is slow and nitrates are plentiful.

“Nitrates are a possibility under current dry conditions but often are hard to predict when they will appear,” Schroeder says. “As growers consider their options for salvaging drought-damaged corn, the natural option is to harvest the crop for silage where livestock, dairy and beef are available to consume it.”

Symptoms of nitrate poisoning include labored breathing, loss of weight and lack of appetite. Clinical signs of nitrate poisoning are related to the lack of oxygen in the blood. Acute poisoning usually occurs from a half hour to four hours after consuming toxic levels of nitrate. The onset of symptoms is rapid.

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

Here are general recommendations for feeding silage containing nitrates to livestock:

• Silages with less than 1,000 parts per million (ppm) of nitrate-N are safe to feed.

• Silages with levels of up to 4,000 ppm should be diluted with other feed to achieve rations with nitrate concentrations of 1,000 ppm or less. Silo gas is another problem with nitrate accumulation in drought-stressed corn.

Silo gas is common in all silages but more so in forage crops such as corn and sorghum. These crops accumulate nitrates from exposure to stress situations, including drought, hail, frost and fertility imbalances.

Nitrates are responsible for lethal silo gas when they combine with organic silage acids to form nitrous oxide. The nitrous oxide decomposes to water and a mixture of nitrogen oxides, including nitrogen oxide, dioxide and trioxide.

These forms of nitrogen are volatilized as a brownish gas in the atmosphere.

This gas is heavier than air and very lethal to humans and livestock.

High nitrate levels probably will not be a problem for producers who used nominal rates of nitrogen fertilizer and have experienced continuous drought since its onset in mid-May. Producers who use manure and those who have had intermittent showers that resulted in 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 percent.”

He also advises producers who green chop or apply manure to take a nitrate test before feeding the material to livestock.

“When in doubt, have the forage analyzed before feeding,” he says. “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.”

Laboratory analysis can be performed on suspected plants, but samples need to be representative of the field or bales in question. Samples should be packaged in a clean plastic bag and shipped to a laboratory for analysis.

The North Dakota Veterinary Diagnostic Laboratory will test such samples. Before mailing a sample, contact the lab by phone at 701- 231-7527 or 701-231-8307.

Ways to reduce nitrates in corn silage include:

• Do not feed the silage until the fermentation process is complete. Fermentation will reduce nitrate levels by 30 to 50 percent.

• Avoid situations in which manure or fertilizer results in very high rates of nitrogen applied on a droughty soil.

• Minimize plant stresses from nutrient deficiencies.

• Harvest on bright, sunny days.

• Do not harvest for at least three days following a soaking rain that comes after a period of dry weather.

• Raise the cutter to leave at least 6 inches of stubble.

• Dilute high-nitrate corn silage with feed grains or hay.

“It is difficult to predict where nitrates may be a problem, but the potential certainly exists,” Schroeder says. “Now is the time to be aware of that risk and manage accordingly.”

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