Dakota Farmer

Manage high nitrates with pregnant cows

With drought altering nitrate levels in plants, manage herd carefully when grazing.

October 14, 2021

4 Min Read
Cow and calf
SYMPTOMS OF POISONING: Signs of nitrate poisoning include difficult breathing, muscular weakness or loss of coordination, blue coloration of mucous membranes, dilated pupils, collapse and death. If you see these symptoms, test your feeds for nitrates. Sarah McNaughton

This year’s drought has brought many challenges for cattle producers. High nitrate levels in feed is one that producers need to be aware of, especially for the reproductive herd.

Nitrates can be found in multiple forages and weeds, such as millet, oats, wheat, corn, sorghum, sudan, kochia, pigweed, lambsquarter, bromegrass and orchardgrass, to name a few. Nitrates are taken up from the soil by the plant’s roots and through photosynthesis. The nitrates are then converted into plant tissue as amino acids, proteins and other nitrogenous compounds.

While all plants contain some nitrates, different management practices and unforeseen events can amplify the amount of nitrates found in forages. Conditions that can alter nitrate levels include:

  • weather (drought, freezing, hail)

  • herbicide and fertilizer applications

  • disease

The level of nitrates in a plant depends on its stage of maturity, soil nitrate level, amount of sunlight and the part of the plant (lowest third of stem has highest nitrate level). As a result, test your forages for nitrate levels prior to feeding.

Feeding pregnant cows

During droughts, grazing standing forage crops, such as millet and sudan, is a common practice. With pregnant females, understand that grazing management is critical to avoid nitrate toxicity and potential abortions.

With the highest concentration of nitrate occurring in the lowest third of the plant, do not force cows to graze more than the leaves and upper stalks. By grazing only the leaves and upper stalks, this will reduce the inflow of nitrates, because animals are allowed to be selective and will consume the higher quality and more-palatable leaf material before the stalk. This is beneficial to decrease toxicity.

Also, consider stocking density of a pasture that may be slightly higher in nitrates. Typically, cows will be selective in their grazing; however, if overstocked, cows can’t be as choosy, and may overgraze plants or ingest weeds, thus resulting in toxicity.

Nitrate poisoning can be lethal at high enough levels. When forages high in nitrate are fed to livestock, the nitrate is converted to nitrite in the rumen. At high enough levels, nitrite, the toxic compound, is absorbed into the blood and causes decreased oxygen carrying capacity throughout the body. With enough nitrates, the oxygen carrying capacity of the animal decreases, which can be lethal.

With a pregnant female, if nitrate levels become high enough, oxygen to the fetus decreases, and early abortions can occur. If abortions are seen in the second and third trimester, where visible dispelled fetuses present themselves, look for brownish-colored blood. This would indicate the fetus lacked oxygen. If more than one female aborts with similar findings, take appropriate action in feeding your reproductive herd. Unfortunately, warning signs of high nitrates in the cow prior to abortions are unlikely seen, as abortions may be the first warning sign.

During conditions of drought, it is a common practice to pregnancy-test the herd early to find any open females. However, doing a later pregnancy check in the fall may be warranted, especially if the reproductive herd begins to show signs of open cows. Potential high nitrates may be to blame for open cows.

Therefore, pay attention to the level of nitrates to ensure cows do not reach a level that compromises fetal health. Abortions due to nitrate poisoning may not be preceded by some symptoms of nitrate poisoning in the pregnant female. Symptoms of nitrate poisoning to watch for include:

  • difficult and rapid breathing, or mouth breathing

  • rapid and weak heartbeat

  • below-normal body temperature

  • weakness or loss of muscle coordination

  • bluish pigmentation around eyes or mucous membranes

  • brownish-colored blood

  • marked dilation of pupils

  • collapse

  • death

If any of these symptoms are noticed, pull animals from the feed source immediately and test the feed.

Managing nitrates

South Dakota State University Extension has a Nitrate QuikTest available for standing forages. Testing prior to feeding forages or putting cows out on forage crops to graze ensures cows do not consume toxic levels of nitrates. If levels of nitrates are high but within a level of caution, proper management when feeding needs to be taken.

Supplementing cows while they adapt to the pasture of higher nitrates is key. This will ensure that cows are full and don’t over indulge, and it allows them to gradually adapt to higher nitrates. If feeding harvested feeds high in nitrates, they can be blended at different rates, depending on the level of nitrates in the forage.

Source: South Dakota State University Extension is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.


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