When high temperatures arrive in the summer months, cool season grasses like fescues and orchardgrass become semi- dormant. These cool season varieties are the base pasture forages that cattle production is based on in the spring and fall in Tennessee. Many beef produces establish warm season summer annual grasses such as sorgum x sudan hybrids and pearl millet to fill the grazing gap from June to September when forages are needed. Also in instances, these warm season grasses are harvested for hay. While these grasses are an excellent source of pasture and hay, they come with a risk.
Nitrate poisoning occurs when cattle consume hay or pasture containing high levels of free nitrates. Under drought conditions, both sorgum x sudan hybrids, pearl millet and Johnsongrass have the potential to accumulate high levels of nitrates, especially if they have been fertilized with nitrogen. Grazing these plants during a drought, or feeding hay that was cut during or just after a drought should be avoided.
Nitrate accumulation occurs because the plant continues to take up nitrogen through the roots, but drought conditions cause an inadequate water supply for rapid plant growth. Nitrates are accumulated in the plant for use in protein formulation 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 or red blood cells to carry oxygen. Animals suffering from nitrite 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 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 until7-10 days of adequate rain. Hay that is suspected of high nitrate levels can be analyzed. For further information contact the Extension office at 823-2735 and UT Extension offers equal opportunities in programs and employment.
