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 arestunted 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.