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Beware Silo Gas and Avoid Silo Filler’s Disease

September 7, 2012

Vermont has been fortunate to not have the depth of drought that the Midwest has suffered, but it has been dry; dry enough for nitrates to be a problem.   Silo Filler’s Disease is a real risk this year.  Although the photo is of silo gas in an upright silo, workers can also be exposed to silo gas around horizontal silos, piles and bagged silage.

What is Silo Gas?  In a dry year, there will be increased nitrates in the corn.  Within a few hours of ensiling, fermentation begins.  Some bacteria use the nitrates in the corn, instead of oxygen for fermentation, forming nitric oxide (NO), a non-lethal gas.  The nitric oxide combines with oxygen in the air, producing nitrogen dioxide (N0₂).

NO₂ is heavier than air and toxic to humans and animals. NO₂ has a yellowish-reddish-brown color. It does have a bleach-like smell,  but with so many odors around the farm, do not rely on odor to alert you to its presence.

Carbon dioxide (CO₂) is also formed in the process, but not often to lethal levels.

Silo gas (the combination of nitrogen dioxide (NO₂) and carbon dioxide (CO₂)) forms within a few hours of ensiling, and continues to be formed for up to 3 weeks after the last silage is added to the silo.

Silo-Filler’s Disease results from exposure to silo gas.  Inhaling even a small amount can result in serious, permanent or fatal lung injury.  The NO₂ combines with water in your lungs and forms nitric acid, which is very corrosive.  A person can become helpless in 2 to 3 minutes when exposed to silo gas.

Symptoms of silo filler’s disease include coughing, burning, shortness of breath, chills, fever, headache, nausea and vomiting. Symptoms may take 3 to 30 hours to develop after a mild exposure to silo gas; the slow, progressive inflammation of the lungs causes a buildup of fluid in the lungs. This can be fatal.

Silo Filler’s disease often relapses in 2 to 6 weeks; this may be milder or more severe than the first episode.

To prevent Silo Filler’s disease, start in the field.  The highest level of nitrate in the corn plant is in the lowest part of the stalk.  Raise the cutter bar; leave 10 to 12 inches of stalk in the field.

  • Cover bunkers and piles immediately after harvesting.
  • Stay out of an upright silo for at least 3 weeks after filling.
  • Don’t open the plastic of a silage bag or bunk/pile cover for at least 3 weeks after ensiling.
  • Ventilate the silo room; keep windows and door to outside open for at least 3 weeks after filling the silo.
  • Keep the door between the barn and the silo room closed for at least 3 weeks.
  • Think about where NO₂ gas may drift from horizontal silos, piles and silage bags.  NO₂ is heavier than air and may collect in low areas or buildings.
  • Do not puncture bubbles that may appear in the plastic.

If exposed to silo gas, see your doctor immediately.  Remember, this can be fatal.

High nitrates in corn can also cause health issues with your animals.  More info is available in this latest Dairy Herd Management issue.  Test the corn and work with your feed dealer.  Although not appearing on their menu, UVM’s Agricultural and Environmental Testing Lab will do nitrate testing for $10.00 per sample.


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