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OMAFRA: Beware of nitrates in forage crops

August 15, 2022  By OMAFRA Field Crop News

Christine O’Reilly, forage and grazing specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), warns that recent weather conditions mean an increased risk of nitrates in forage crops. She says the risk is higher for the five to seven days after a rain that ends a severe dry period; nitrates are cause for concern because they can increase silo gas production and cause nitrate poisoning in livestock.

Silo gas (nitrogen dioxide, N2O) is produced almost immediately after filling a silo. It has a bleach-like odour and may be visible as a reddish-brown haze. However, it is not always visible. It is difficult to predict when silo gas will be produced, so always take precautions following harvest. People exposed to silo gas are at risk of severe respiratory distress, permanent damage to lungs, and even sudden death.

Nitrates (NO3-N) in forage are converted to nitrites (NO2-N) in the rumen. When there are high levels of nitrates in the feed, the rumen microbes cannot keep up with nitrite production. The nitrites form methemoglobin in the blood, which reduces oxygen-carrying capacity. Signs of acute nitrate poisoning in animals include staggering, vomiting, laboured breathing, blue-grey mucous membranes, and death (typically within three hours).


Testing the forage is the only way to know whether the level of nitrates may pose a problem. Be sure the sample is representative of the feed; it should be frozen to keep the nitrate levels from changing between the farm and the lab. |READ MORE


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