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Dry conditions followed by an early frost is a recipe that often causes high nitrate levels in corn silage. These high nitrate levels can lead to nitrate poisoning in cattle and the formation of toxic silo gas. This situation can be further aggravated by high nitrogen fertilization caused by heavy fertilizer or manure applications, or following legume plow down.

When animals eat this nitrate-rich material, the nitrates are rapidly converted to nitrites which are absorbed into the blood stream. Nitrite in the blood alters the way the blood carries oxygen and causes rapid breathing, fast and weak heartbeat, muscle tremors, staggering and death if corrective steps are not taken quickly.

In normal growing conditions, much of the nitrate is taken up by the cobs and converted to protein. When there are few (or no) cobs, nitrate content of the stalks will be higher so be careful when green chopping corn this year as nitrates may be considerably higher than normal. Higher cutting height will help, as nitrates are more concentrated in the bottom 4 to 6 inches of the stalk. Ensiled the corn helps and often reduces the nitrate levels by 25 to 65 percent.

Because of this concern, I sampled four fields for nitrate concentration. I selected fields with varying degrees of drought stress and frost damage. The table below illustrates the range in nitrate concentration. As you can see, some samples have dangerous levels of nitrates, part of which should disappear during fermentation -- but also increases the risk for deadly silo gas.

Bottom: lower plant (0 – 24 inches)
Top: middle or top (24-48 inches)

When high nitrate forage is ensiled, deadly nitrogen dioxide gas (silo gas) can be produced within hours! Silo gas is heavier than air, so it settles in low points in the silage pack and in feed rooms at the base of the silo. The gas may be visible as reddish to yellowish-brown haze around the silo base, and has a bleach-like odor.

Protect yourself, your staff and your family from this dangerous poison. If someone must enter the silo to level or cover the silage, do it immediately after filling and leave the blower running while anyone is in the silo. Do not enter the silo for at least three weeks after ensiling. Post a sign at the silo chute as a reminder of the danger. Silo gases can be deadly!

If you suspect high nitrates in the corn, have it tested by a forage-testing laboratory, it’s simple and inexpensive ($11.00). Sample bags and envelopes are available at the Extension office. Sample after ensiling and when fermentation is completed (at least 3 weeks), unless you are using it as green chop.

Reference: Ontario Ministry of Agriculture