Livestock are at higher risk of nitrate poisoning during a drought, according to North Dakota State University Extension Service range and livestock specialists.
Nitrate poisoning may occur if livestock eat drought-stressed crops and forages, which can accumulate nitrates. Feeding drought-stressed forages from oats, barley and corn causes the majority of nitrate poisoning cases in North Dakota.
“However, a number of other plants also can accumulate nitrate, including wheat, sudangrass, sorghum-sudan hybrids, turnips and pearl millet,” rangeland management specialist Kevin Sedivec says. “If producers are considering utilizing low-yielding crops as livestock forage, they should be tested for nitrates prior to feeding.”
Plant stresses, such as drought, can increase the levels of nitrate in plants. Nitrate accumulation is influenced by various factors, such as moisture and soil conditions, and type of plant.
“Not all drought conditions cause high nitrate levels in plants,” says livestock environmental stewardship specialist Miranda Meehan. “Some moisture must be present in the soil for the plant to absorb and accumulate nitrate. In plants that survive drought conditions, nitrates are often high for several days following the first rain.”
Grazing Drought-stressed Plants
Carl Dahlen, beef cattle specialist, has this advice for producers who are scouting or sampling for nitrates in cereal crop fields they are planning to have their livestock graze: “Severe drought-stressed areas such as hilltops with very sandy soils might have plants that look bad, but these plants may be so stressed that they are not accumulating much nitrate at all unless there is a recent rain event.
“Plants have to be in active growth stages to take up nitrogen from the soil,” he says. “Nitrate hot spots in fields have had moisture, so although they are stunted in growth, they typically look very lush and green. Stress from the period from plant jointing to heading is associated with more nitrate accumulation. Fields that had nitrogen fertilizer applied are also more susceptible to accumulating nitrates.”
Nitrate toxicity isn’t an issue on rangelands, Sedivec says. However, pastures with nitrate-accumulating broadleaf plants such as kochia, pigweed and Russian thistle can be a problem because these plants usually are green, so livestock will consume them.
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. Thus, the risk of poisoning can be reduced when haying by raising the cutter bar above 6 inches or by monitoring grazing livestock and removing them when the stubble height of the plants is at 6 inches, the specialists note.
“Ruminant animals, such as cattle and sheep, are susceptible to nitrate poisoning because their digestive process converts nitrate to nitrite, which in turn is converted to ammonia,” explains Janna Kincheloe, area Extension livestock systems specialist at NDSU’s Hettinger Research Extension Center. “When nitrate levels are high, the nitrite will accumulate and be absorbed by red blood cells, reducing their ability to transport oxygen.”
The same reaction takes place in horses’ hindgut; however, the reaction occurs to a much lesser extent, thus nitrate poisoning is very rare in horses.
Signs of Nitrate Poisoning
Clinical signs of nitrate poisoning are related to the lack of oxygen in the blood. Acute poisoning usually occurs from a half-hour to four hours after livestock consume toxic levels of nitrate. The onset of symptoms is rapid. Those symptoms include:
Pregnant females that survive nitrate poisoning may abort because of a lack of oxygen to the fetus. Abortions generally occur approximately 10 to 14 days following exposure.
Laboratories can perform an analysis 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 a laboratory. Producers can send samples to the NDSU Veterinary Diagnostic Laboratory, Van Es Hall, Fargo, ND 58105-5406. For more information, contact the lab at 701-231-8307.
Preventing Nitrate Poisoning
The best way to prevent nitrate poisoning is to control the type and quantity of forage offered to livestock, the specialists say. They recommend:
“Also be sure you don’t overstock pastures when grazing high-nitrate forages,” Meehan advises. “Overstocking increases the amount of high-nitrate plant parts (stems and stalks) that are consumed by livestock.”
The nitrate content of small-grain forages also can be reduced by up to 50 percent by chopping and ensiling, Dahlen says. Producers should make sure the silage has time to ferment (21 days), then test the silage before feeding it and dilute it with other feeds if necessary.
For more information on nitrate poisoning, check out the NDSU Extension publication “Nitrate Poisoning in Livestock” at http://tinyurl.com/NitratePoisoning.
Source: North Dakota State University
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