However, the more common type of silo is the non-airtight silo which is unloaded from the top. Oxides of nitrogen are concentrated in the chamber above the silage. The percent of nitrate in the plant material ensiled determines how much oxides of nitrogen are produced. Most reports of silo-filler's disease have been reported with silos filled with com silage where the entire plant is chopped into small chunks. Factors which increase the nitrate content of plants incl des drought followed by rain and prolonged cloudy weather, plants with leaf and root damage, and plants grown in soil with high levels of nitrogen.
Most farmers are aware of the hazards of entering a silo soon after filling stops.
The Mayo Clinic reported seeing 12 patients with silo gas exposure from 1980 - 1987. There are an estimated 15,000 silos on dairy farms in Michigan. Silo - Filler's Disease. All exposures had occurred in conventional top-unloading silos. In one patient, hypoxemia and transient obstruction of the airways developed, but no pulmona y infiltrates were noted.