Nitrates are accumulated in the plant for use in protein formation when adequate water becomes available. When the animal consumes a plant with high nitrate levels, the nitrogen is converted from nitrate to a form called nitrite. These nitrites get into the blood stream and interfere with the ability of red blood cells to carry oxygen. Animals suffering from nitrate poisoning exhibit labored breathing, muscle tremors and staggering. Membranes of the eyes and mouth are bluish because of the lack of oxygen.
Death can occur relatively quickly.
Prevention is the best way to deal with nitrate toxicity. If any pasture is suspected of having high nitrate levels, avoid grazing these pastures until seven to 10 days after an adequate rain. Hay that is suspected of having high nitrate levels can be analyzed. Contact your local Extension office for more information. Table 1 lists a scale of the toxicity of increasing nitrate levels in hay.