This summer has been defined by the continuing drought across most of the West. Pastures are dry, fields are running out of water, hay prices are high and most of what is left for grazing has been stressed by our continued drought. Drought-stressed forages are notoriously at risk for nitrate (NO₃) accumulation, which can cause nitrate poisoning in our livestock. If you are planning on grazing any small grains regrowth, they should be tested and monitored for nitrate accumulation.

Carmen Willmore

Extension Educator / University of Idaho Extension – Lincoln County

Email Carmen Willmore

Under normal conditions crops would accumulate high levels of nitrate until heading, but then much of the nitrate would be metabolized as the plant converted nitrate into amino acids and proteins for grain fill. However, without moisture, the growth of the plant slows, and nitrates aren’t utilized as quickly, causing accumulation.

Nitrate accumulation is more of an issue in crops such as oats, barley, wheat and sorghum than others such as alfalfa and grass hays. Also, some weeds, such as lamb’s-quarters and pigweed, can become nitrate accumulators and pose significant poisoning stress if consumed in large quantities or if they are present in fields that are to be green chopped.

The best practice to prevent poisonings is to test for nitrates. There are three tests available:

• Nitrate quick test – a qualitative test which detects the presence of NO₃ with a change in color from the testing solution.
• Laboratory analysis – samples are sent to a certified lab using wet chemistry methods to analyze for the presence of nitrates.
• Nitrate strip test – a semiquantitative test that involves more processing of the forage sample prior to testing but can be faster than sending a sample off to the lab and more accurate than the quick test.

(Further information for these tests is available online at the Montana State University Extension website.)

Forages that have a nitrate level of less than 1,500 parts per million (ppm) are safe to be utilized by all classes of livestock. Between 1,500 – 5,000 ppm, NO₃ should be limit-fed for calves and pregnant or lactating animals. Weaned stocker calves can be transitioned onto fields in this range, while monitoring the forage for any change in nitrate level and animal health. Forages testing between 5,000-10,000 ppm NO₃ should be limit-fed at 25%-50% of the ration for growing cattle and should not be fed to pregnant animals. Any forages over 10,000 ppm NO₃ should not be fed to any class of livestock.