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Nitrates in forages are risk for pregnant cows

Nitrates in forages are risk for pregnant cows

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Pregnant cow

When grazing pregnant females, management is critical to avoid nitrate toxicity and potential abortions.

Drought poses many challenges to the beef cow herd. Nitrates in feed is one of those challenges that producers need to be aware of, especially in the reproductive herd.

Nitrates can be found in multiple forages and weeds, such as millet, oats, wheat, corn, sorghum, sudan, kochia, pigweed, lambsquarter, brome grass and orchard grass, to name a few.

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 and disease.

The level of nitrates in a plant is dependent on stage of maturity, soil nitrate level, amount of sunlight/shade and the part of the plant (lowest one-third of the stem will contain the highest level of nitrate).

As a result, it is important to test your forages for nitrate levels prior to feeding.

Feeding pregnant cows

During this time, cows will most likely still be in the first trimester of pregnancy, depending on operation-specific breeding seasons. A majority of cattle are still out on standing forages if not being moved to subsequent standing forages.

During drought conditions, grazing standing forage crops (such as millet, sudan, etc.) is a common practice.

With the highest concentration of nitrate occurring in the lowest one-third of the plant, do not force cows to graze more than 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 prior to the stalk. This is beneficial to decease toxicity.

It is also important to consider stocking density of a pasture that may be slightly higher in nitrates. Typically, cows will be selective in their grazing; however, if overstocked, this allows for less opportunity to be selective and more opportunity to overgraze or ingest weeds, thus resulting in toxicity.

Nitrate poisoning can be lethal at high enough levels. When forages high in nitrates are fed to livestock, it 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.

This becomes important when considering a pregnant female. If levels of nitrates 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 the oxygen it needed for survival.

Unfortunately, warning signs of high nitrates in the cow prior to abortions are unlikely.

Potential high nitrates may also be to blame for open cows.

Managing nitrates

Testing prior to feeding forages or putting cows out on forage crops to graze is important to ensure cows do not consume toxic levels of nitrates.

If feeding harvested feeds high in nitrates, they can be blended at different rates, depending on the level of nitrates in the forage.
Symptoms to be aware of if nitrate poisoning is occurring include difficult and rapid breathing, mouth breathing, rapid and weak heartbeat, below-normal body temperature, muscular weakness, loss of muscle coordination, blue coloration of mucous membranes, marked dilation of pupils, collapse and death.

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

Olivia Amundson, South Dakota State University Extension cow/calf field specialist, wrote this for the university’s website.

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