Test for nitrate levels
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Jack Stivers
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Producers harvesting forage variety cereal crops for hay — such as oats, beardless barleys, beardless wheat and triticale — should be aware of potential high nitrate levels in the forage, especially when growing under adverse conditions, including drought stress, heat stress, prolonged cool temperatures, hail, diseases and high levels of soil nitrogen. All plants contain nitrate, but nitrate levels toxic to livestock are mostly associated with forages, hay, pasture or weeds. Nitrate itself is not toxic to animals, but at elevated levels it can cause a non-infectious disease called nitrite poisoning. Nitrate normally found in forage consumed by ruminant animals is broken down to nitrite and then to ammonia. The ammonia is then converted to protein by microbes in the rumen. Ruminant animals with high nitrate levels in their diets accumulate nitrite. Nitrite is absorbed into the blood and combines with hemoglobin to form methemoglobin, which causes a reduction in the ability of the blood to carry oxygen from the lungs to body tissues. When the blood can no longer supply oxygen to the body, the animal can suffocate.
Producers should never assume their forage levels are safe if they know a crop was exposed to any adverse growing conditions that can increase nitrate accumulation. Higher nitrate levels are usually present in immature plants and decrease as plants mature. Nitrate concentration is highest in the stems, especially in the lower third of the stem and at the nodes. An intermediate level usually exists in leaves and very little is found in the grain. Avoid cutting when nitrate concentrations are at peak levels. For example, toxic levels of nitrate can accumulate in forages immediately after drought-ending rain or irrigation. Since peak nitrate levels occur in the morning, delay haying or grazing until the afternoon of a sunny day.
Take precautionary measures if you suspect high nitrate concentrations prior to harvesting or feeding forage. Even under ideal conditions, nitrate accumulation is unpredictable. Nitrate concentration can vary in areas of a single field; therefore, nitrate testing is advised in many situations.
