VPT 421: Veterinary Toxicology (2+0)

NITROGEN DIOXIDE POISONING

• Animals are exposed to nitrogen dioxide in two ways.
• It is formed in fermenting silage and also is produced within the rumen from plant nitrates.
• It is postulated that high rates of fertilization increases the nitrate contents of plants.
• When the nitrate containing forage is fermented in silo, nitric acid is formed which then breaks down to release NO and N0 ₂•
• Cattle, pigs and chickens have been reported to die from exposure to this gas.
• It causes pulmonary lesions.
• The effects of N0 ₂ in the lung are likely to be initiated by the peroxidation of lipids.
• A condition in man known as "silo fillers disease" has been shown to be due to inhalation of nitrogen dioxide formed in silos.
• The safety limit value for continuous exposure is only 1 ppm.
• Animals have survived exposure of 25 ppm.
• Symptoms include apnoea, progressive dyspnoea, lacrimation, excessive salivation, grunting, anorexia, emaciation and dehydration.
• Pathologic changes include methemoglobinemia, dark red kidneys and necrosis of skeletal muscles.
• Pulmonary lesions are hyperemia, edema, hemorrhage, bronchiolitis, infarction and emphysema.
• No specific treatment is available.