Test Forages for Nitrate Before Haying or Grazing

Russell Nemetz

and some may have the potential to contain toxic levels of nitrate.

According to the National Agricultural Statistics Service, North Dakota

producers planted 70,000 acres of hay and haylage last year. Many of these acres

consist of annual forages, small grains and cover crops.

"Although these forages are a great option for haying or grazing, they could

pose a risk of nitrate toxicity for livestock," says Janna Block, livestock

systems specialist at NDSU's Hettinger Research Extension Center.

Nitrate toxicity is a potential issue for livestock consuming small-grain

forages (wheat, oats, rye, triticale and barley), brassicas, millet, sorghum and

sudangrass, and standing corn or corn used for hay. Although nitrates typically

are not an issue on rangelands, pastures with nitrate-accumulating weeds such as

kochia, lambsquarters, pigweed, quackgrass and thistle also may be a problem.

Nitrate toxicity is most commonly a problem in ruminants, with cattle more

susceptible than sheep.

"Nitrate is a common form of nitrogen found in the soil, which is taken up by

plants and converted to protein through the process of photosynthesis," Block

explains. "Under normal growing conditions, nitrate does not accumulate in the

plant. However, when plants encounter stressful growing conditions,

photosynthesis is inhibited and the potential for accumulation of nitrates is

increased.

"In general, people associate an increased risk of nitrate toxicity with

drought," Block adds. "The current U.S. Drought Monitor for North Dakota

indicates that over half of the state is abnormally dry for this time of year,

mainly in the western counties."

Block notes, "It is important to recognize that drought is not the only

condition that can lead to nitrate accumulation. Prolonged cool temperatures and

cloudy conditions also can disrupt the conversion process and cause nitrate to

build up in plants. Additionally, nitrates may accumulate due to conditions that

reduce leaf area and limit photosynthesis, such as frost, hail or disease."

When beef cattle consume increased quantities of nitrate, it overwhelms the

ability of rumen microbes to convert nitrate to protein. This results in a

buildup of nitrite in the rumen, which is 10 times more toxic than nitrate.

Excess nitrite is absorbed into the bloodstream, which removes the blood's

ability to carry oxygen and causes the animal to suffocate. Cases of

lower-level, chronic toxicity also can occur. In those cases, producers may

observe weight loss, night blindness and abortions in their cattle.

Here are several strategies to reduce the risk of nitrate toxicity:

* If applying nitrogen fertilizer, divide the total application into two or more

treatments.

* Control potential nitrate-accumulating weeds in pastures.

* Avoid cutting forage or allowing cattle to graze it in the morning, when

nitrate levels are at their highest.

* Consider raising the cutter bar when harvesting forage because the majority of

nitrates accumulate in the lower one-third of the stem.

* Consider delays in harvesting to allow plants to mature because nitrate levels

are typically greatest in young plants. Keep in mind that mature plants still

can contain excess nitrate and this strategy can result in decreased forage

quality.

"Producers planning to graze nitrate-accumulating forages should take additional

steps to minimize risks," Block advises. "Nitrate concentration can be extremely

variable within areas of a field, and predicting and managing grazing animals'

intake is difficult."

Here are some other ways to help reduce the nitrate risk:

* If possible, avoid grazing by pregnant, sick or thin animals due to increased

susceptibility.

* Stock lightly so animals can select leaves and are not forced to eat the lower

portions of stems.

* Ensure that cattle receive a full feed of hay before turnout and observe

cattle frequently for the first week or so of grazing.

* Provide energy supplements to help rumen bacteria convert nitrate to protein.

"The most important recommendation is to test for nitrates prior to grazing or

haying," Block says.

Many NDSU Extension offices have access to a Nitrate QuikTest, which is a

screening tool to assess whether nitrate is in standing forage. Extension agents

who have been certified can conduct the test in a field or office setting.

Producers should provide a representative sample of at least 20 stems by

clipping them to ground level while traveling in a zigzag pattern across the

field.

"If nitrates are present in the sample, producers should delay grazing or

harvesting for several days and then re-test," Block says. "Samples also can be

submitted to a laboratory for quantitative analysis to further assist with

management decisions."

The Nitrate QuikTest is not designed to evaluate nitrate content in harvested

forages. The best testing strategy for forages that have been cut and baled is

to use a bale probe to collect core samples and submit them to a laboratory for

analysis.

Ideally, 10% of bales or at least 20 core samples per lot of forage should be

collected. A lot is defined as hay harvested within 48 hours from the same

field.

Nitrate concentrations do not decrease through time in stored forages because

photosynthesis is required for conversion of nitrates in the plant. Ensiling can

decrease nitrate content through fermentation, but samples still should be

submitted for analysis to determine accurate levels.

"Producers need to understand the potential risks of nitrate toxicity and the

factors leading to nitrate accumulation in plants," Block says. "Determining

actual levels of nitrate present in grazed and harvested forages hay is critical

to be able to utilize these feedstuffs in a safe manner."

For more information about nitrate toxicity, contact your local NDSU Extension

agent or check out the NDSU Extension publication "Nitrate Poisoning of

Livestock,"

(https://www.ag.ndsu.edu/publications/livestock/nitrate-poisoning-of-livestock).