Nitrate Levels in Forages and Water

Author: Charles C. Stallings, Professor and Extension Dairy Scientist, Virginia Tech, Blacksburg

Publication Number 404-163, Posted August 2006


Nitrate-nitrogen is the form of nitrogen usually taken up by growing plants. High levels in forages can interfere with the ability of the animal to transport oxygen in the blood. An animal with labored breathing or that is staggering or panting is exhibiting symptoms of inadequate oxygen being delivered to tissues.

Nitrates are very water-soluble, easily absorbed by plants, and accumulate when their growth is slowed. This can be from a lack of water or other nutrients. Nitrates tend to concentrate in the stem of the plant with little in the grain. When the plant is actively growing, the nitrates will be converted to plant protein. This stops when plant growth stops. A minimum of three days of growth is needed to reduce plant nitrate levels after a rain.

Certain species of plants such as sorghum and sudangrass tend to accumulate nitrates more than other species. Even in normal years, these plants may have elevated nitrate levels. However, alfalfa, barley, corn, millet, oats, and rye all can have high levels of nitrates under the right conditions. Johnsongrass can also be high in nitrates and can be a problem in highly infested sites.

Do not feed freshly chopped plants or hay made from drought-stressed plants. Ensiling will reduce nitrates by about 50 percent. Usually it is best to wait at least three weeks after ensiling before feeding. It is possible to check plants for nitrates before feeding by sending a sample to a forage-testing laboratory.

Nitrates are usually expressed as either nitrate or nitrate- nitrogen as a percent of the dry matter. Make sure you know which unit is being expressed since there is a 4.4-fold difference. Since nitrogen makes up only a portion of the nitrate molecule, expressing it as nitratenitrogen will result in a smaller number than expressing as nitrate. The relationships in Table 1 have been proposed by Teutsch and Meldrum and are in line with other recommendations (Ishler et al.)

Table 1. Breakdown of nitrate and nitrate-nitrogen levels in feedstuffs and guidelines for feeding.
Nitrate, % DM
Nitrate-N, % DM
Guidelines
0 - 0.25
0 - 0.06
Considered safe
0.26 - 0.50
0.06 - 0.11
Can be a problem for pregnant and young animals, limit to 50% of ration dry matter
0.51 - 1.5
0.12 - 0.34
Danger; limit to 25% of ration dry matter
1.5+
0.34+
Potentially toxic; do not feed
Source: Teutsch and Meldrum, 2006

Another source of nitrates is water. Take care if you are feeding high-nitrate forages with water that is high in nitrate. Animals that have been exposed to nitrates in either forages or water do tend to have increased tolerance, but toxicity can still result. Typically, nitrates in water less than 45 parts per million (PPM) can be considered safe and nitrates over 221 PPM could be harmful or even toxic, especially if forages are high in nitrates (National Research Council, 1974). Intermediate levels might be harmful over a prolonged period of exposure. A more complete breakdown is presented in Table 2.

Table 2. Breakdown of nitrate and nitrogen-nitrogen levels in water
Nitrate, PPM
Nitrate-N, PPM
Guidelines
0 - 44
0 - 10
Considered safe for ruminants
45 - 132
10 - 20
Generally safe in balanced diets with low nitrate feeds
133 - 220
20 - 40
Could be harmful in consumed over long periods of time
221 - 660
40 - 100
Cattle at risk; possible death
661
100
 Unsafe; do not use
Source: National Research Council, 1974

Precautions When Using Feeds with High Levels of Nitrates

  1. Ensile forage, if possible, to reduce nitrate levels. It is best to ensile for three weeks before feeding; however, any ensiling is better than none. Making material into dry hay does not reduce nitrate levels.

  2. Raise the cutter bar during chopping to leave more of the stalk in the field and reduce nitrate levels.

  3. After a rain, wait at least three days before chopping drought-stressed corn plants to allow nitrates to be converted in the plant.

  4. Introduce feeds containing nitrates slowly and do not allow access when cows are extremely hungry.

  5. Dilute forages containing nitrates with clean feeds by using another forage and/or high-fiber by-products such as whole cottonseeds, brewer’s grains, etc.

  6. Feed a balanced ration with adequate nutrients, especially vitamin A.

  7. Young, growing, and pregnant animals are the most susceptible to nitrates and should be observed for signs of toxicity if given feeds containing nitrates.

  8. There are no magic feed additives to counteract the effect of nitrates.

  9. Avoid water with high levels of nitrates.

  10. Test feeds after ensiling if there is reason to expect problems with nitrates.

References

Ishler, V.A., Heinrichs, A.J., Buckmaster, D.R., Adams, R.S., and Graves, R.E. Harvesting and utilizing silage. Penn State Cooperative Extension Circular 396.

National Research Council. 1974. Nutrients and toxic substances in water for livestock and poultry. Washington D.C. National Academy Press.

Teutsch, Chris, and Meldrum, Blair. Summer 2006. The Virginia Forager newspaper, page 10.

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