August 28, 2003

 

Nitrate Poisoning of Livestock

When in doubt, have drought-stressed feeds and forages analyzed for nitrate before grazing or feeding. That’s the advice of Charles Stoltenow, North Dakota State University veterinarian and Greg Lardy, NDSU beef specialist.

The majority of nitrate poisoning cases in North Dakota occur with drought-stressed oats, corn and barley. However, a number of other plants can also accumulate nitrate, including sudangrass, sorghum-sudan hybrids and pearl millet.

"Plant stresses such as drought are associated with increased levels of nitrate in plants," Stoltenow says. "Nitrate accumulation is influenced by various factors such as moisture and soil conditions and type of plant."

Plant parts closest to the ground contain the highest concentrations of nitrates. Leaves contain less than stalks or stems while the seed and flower usually contain little or no nitrate. "While difficult to do with drought-stressed forages, raising the cutter bar above 6 inches can reduce nitrate content of forages," Lardy says. "Research has shown that the lower 6 inches off the stem in pearl millet contains three times more nitrate than the top part of the plant."

Not all drought conditions cause high nitrate levels in plants. Some moisture must be present in the soil for the plant to absorb and accumulate nitrate. If the major supply of nitrates for the plant is in dry surface soil, the roots will absorb very little nitrate. In plants that survive drought conditions, nitrates are often high for several days following the first rain.

Clinical signs of nitrate poisoning are related to the lack of oxygen in the blood. Acute poisoning usually occurs between a half hour to four hours after consuming toxic levels of nitrate. Onset of symptoms are rapid and include:

• Bluish/chocolate brown mucous membranes
• Rapid/difficult breathing
• Noisy breathing
• Rapid pulse (150+/min)
• Salivation, bloat, tremors, staggering
• Weakness, coma, death
• Dark "chocolate-colored" blood

"Pregnant females that survive nitrate poisoning may abort because of a lack of oxygen to the fetus," Lardy says. "Abortions generally occur approximately 10-14 days following exposure to nitrates."

Laboratory analysis can be performed on suspected plants but samples need to be representative of the field or bales in question. Samples should be packaged in a clean plastic bag and shipped to the laboratory for analysis.

"Animals can be treated by intravenous injections of methylene blue," Stoltenow says. "But you must consult your veterinarian before using the treatment because methylene blue is not approved by the FDA for use in food-producing animals."

Prevention of nitrate poisoning is best achieved by controlling type and quantity of forage, Lardy notes. Avoid forages with potentially toxic levels or at least dilute them with feeds low in nitrate. When grazing, feed dry roughage first to reduce the amount of affected plants ingested by hungry animals.

Harvested forages that are high in nitrate can often be safely fed by mixing with other feeds to reduce the total dietary intake of nitrate. "Contact your veterinarian or extension office if you need assistance in determining the correct ratios of high and low nitrate forages to blend to develop a ration for a particular class of livestock," Stoltenow says.

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Source: Greg Lardy, (701) 231-7660, gregory.lardy@ndsu.nodak.edu
Charles Stoltenow, (701) 231-7522, charles.stoltenow@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu