silage gas can occur during silo filling if you don't take
precautions. Protect yourself and your livestock from injury
or death by avoiding this potential danger.
Silage fermentation may produce several kinds of gas, including
carbon dioxide and nitric oxide. Although carbon dioxide is
non-poisonous, it can cause suffocation.
oxide chances to nitrogen dioxide when it contacts oxygen
in the air. Nitrogen dioxide (NO2) is poisonous
and can injure and kill people as well as livestock.
Wisconsin farmers have reported serious lung injury from inhaling
small amounts of silage gas, and some have suffered permanent
damage. Numerous other cases have probably gone unreported.
Silo gas severely irritates the upper respiratory tract and
may inflame the lungs, even though the farmer may experience
little immediate pain or ill effects. However, he may die
later due to fluid that collects in the lungs.
people who develop the initial symptoms also develop additional
symptoms. Frequently, a relapse with symptoms similar to pneumonia
occurs one to two weeks after initial recovery from the exposure.
This is why it's important for the victim of silo gas exposure
to get immediate medical attention.
dioxide is a hazard on the farm because:
a brief exposure can be fatal.
of nitrogen dioxide from nitric oxide may occur whenever
silage is made.
is a popular, highly desirable feed, which is produced on
many Wisconsin farms.
Shortly after ensiling green plant material, oxygen is used
in fermentation and the nitrates in the plant are released as
nitric oxide (NO). This gas quickly escapes from the silage
and combines with oxygen in the air to form toxic nitrogen dioxide.
lethal gas is yellowish-brown and smells like some laundry
bleaches. After more oxidation, it forms N2O5,
which then forms highly corrosive nitric acid when combined
with water. Since oxidation may occur in the lungs, nitrogen
dioxide can produce permanent lung damage.
Since nitrogen dioxide is heavier than air, it remains beneath
the air mass over the silage. It layers on top of the silage
below the upper edge of the top door or settles down through
the chute. It may also seep through the drain at the base of
the silo, or it may be present in the unloading chamber at the
bottom of oxygen-limiting silos. It often concentrates in the
silo room and moves into the barn. It leaves a yellow stain
on silage, wood or other materials it contacts.
Some environmental conditions (particularly drought), cause
nitrates to accumulate in plants fertilized with nitrogen, even
at recommended rates. But by taking precautions, you may fertilize
at recommended rates for maximum production of silage crops
without fear of nitrogen dioxide production. Proper fertilization
combined with good cultural methods (proper weed, insect and
disease control) reduce the chances of nitrogen dioxide gas
production when you ensile the crop.
While growing the crop:
adequate nitrogen, but don't overdo. As a guide, corn needs
1.2 lbs. of N per bushel yield, oats and/or sudangrass used
for silage should have no more than 75 lbs, of N available
for each harvest. Since this includes both N in the soil
and that applied, follow the recommendations on soil analysis
balanced N-P-K fertilizers, add minor elements if needed.
disease and insect resistant varieties and/or spray to control
insect and disease damage to leaves and roots.
fields relatively free of weeds. Weeds can make silage dangerous
even though there is no nitrate in the corn itself.
a drought, plants rapidly take up nitrate following rain.
So, harvest the crop before fall rains, or wait at least
five days after a rain.
damaged by hail or frost should be harvested immediately
before they take up nitrates.
reduce the amount of nitrate going into the silage, cut
higher than normal (10 to 12 inches). Most nitrates are
in the lower stalk.
filling the silo:
greatest danger from nitrogen dioxide gas from silage is
during the first 12 to 60 hours after filling. However,
take care to avoid possible exposure for 10 days after filling
the silo, and when opening the silo for feeding.
on the alert for bleach-like odors and/or yellowish-brown
fumes in or near the silo. Small amounts of the gas may
not be visible or easily detected by smell, but are still
out of and away from the silo right after filling and during
the following 10 days.
you must enter the silo. first run the silage blower for
15 to 20 minutes. Never enter the silo alone during
the danger period.
the upper chute doors down to the level of the settled silage.
This allows the gas to flow down the chute and keeps it
from collecting in the silo. Be sure to run the blower
first and ventilate the silo chute with fans. Several
people have died in Wisconsin because they didn't ventilate
before going up the chute to remove the upper door.
the silo room adequately for at least two weeks after filling.
Open the windows and outside door of the silo room and use
fans if necessary.
the door between the silo room and the barn closed to prevent
nitrogen dioxide gas from killing livestock.
enclosed silo areas to prevent children and strangers from
entering the silo room and silo.
you experience the slightest throat irritation or coughing
in the silo, get into fresh air quickly and stay away from
the silo area as long as gas may be present.
can make test discs as follows, and hang them at the bottom
of the silo chute to detect gas. Mix a solution of two grams
corn starch and two grams potassium iodide in three ounces
of water. Spray the solution on the filter-paper disc until
soaked. Dry in oven at 100 to 125øF. Fold transparent tape
over one edge and make hole for hanging. Wet the disc with
water and hang it at the bottom of the chute, or inside
the chamber of bottom-unloading silos. If the disc turns
purple, gas i present. Discs may only be used once.
your doctor immediately after exposure to silage gas. Treatment
will prevent lung damage and keep pneumonia from developing
follow these precautions, you can make silage safely. Silage
is an excellent livestock feed and the hazard of toxic gas
production shouldn't discourage you from making and feeding
grass or corn silage.
Nitric oxide gas is produced from ensiled plants that contain
tree nitrate (NO3-
) which hasn't been converted to
protein. Normally, nitrogen is taken up by plants as nitrate
and converted to protein during growth. But when plant growth
is retarded by adverse growing conditions or when excessive
amounts of nitrogen are available in the soil, nitrates not
converted to protein accumulate in the plant stems and leaves.
such plants are ensiled, the nitrate present may be converted
to nitric oxide or it may be lost in the seepage. Even though
much nitric oxide escapes during ensiling, enough nitrate
may remain in the silage to poison livestock in feeding (see
A1889, Protect Livestock from Nitrate Poisoning).
1. Maximum percentage of dry matter as NO3-
sudan grass, sorghums
wheat, barley, rye
nitrate if they take up more than they can convert to protein,
some plants store more nitrate than others. Analyses of plants
in Wisconsin revealed maximum percentages of stored nitrate
(see Table 1).
silage is less apt to produce nitrogen dioxide gas than other
ensiled crops. Weeds in the ensiled crop may produce nitric
oxide (or nitrate poisoning) even when the crop itself is
low in nitrate. ALL weeds commonly present in corn fields
store nitrate under ALL growing conditions.
summer drought followed by rain just before ensiling.
levels of nitrogen in the soil created by excessive fertilization
with commercial nitrogen or a combination of commercial
nitrogen, barnyard manure, and/or plowing down leguminous
green manure crops.
N-P-K fertility (especially high N, low P-K).
temperature (too cold for corn, too hot for oats).
prolonged cloudy weather, or dense stands which reduce photosynthetic
damage:from partial drought, frost, insects, diseases or
chemicals-while the stem remains active.
damage:from cultivation, insects, diseases or chemicals.
The following two publications are available through your county
Weed Control Will Prevent Lowland Abortion in Cattle
How to Protect Livestock from Nitrate Poisoning
Publication #: A1871
is Fact Sheet and apart of
a series from the Department of Agricultural Journalism, College
of Agricultural and Life Sciences, University of Wisconsin-Madison,
Madison, Wisconsin, 53706.
Sund, emeritus professor of agronomy; R.P. Niedermeier, professor
of dairy science; R. H. Burris, professor of biochemistry,
College of Agricultural and Life Sciences, University of Wisconsin-Madison,
Madison, Wisconsin, 53706.
Disclaimer and Reproduction Information: Information in
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