Keep an eye out for nitrate toxicity

By Jeremiah Vardiman

This year has been interesting with droughts and high-priced hay. As cattle transition from rangelands into croplands or feedyards, it is imperative producers be aware of nitrate toxicity. 

Although nitrate toxicity is nothing new, it is still necessary to keep a diligent eye on forages that are at risk of nitrate accumulation and watch for symptoms of nitrate poisoning in livestock, particularly cattle. The need for a close eye increases if producers are sourcing cereal hays or grazing regrowth in grain crops.

Risk of toxicity

Known as “oat hay poisoning” since the 1930s, nitrate toxicity is the excessive consumption of nitrates by livestock, which can result in death. The severity of nitrate toxicity is a combination of the amount consumed and the duration of the exposure to forage with high nitrate levels. 

The toxicity can occur by acute or chronic situations. Acute toxicity is the consumption of large amounts of high-nitrate forages in a short period, while chronic toxicity is the consumption of small amounts of high-nitrate forages over long periods of time.  

Nitrate poisoning is related to the lack of oxygen in the blood. Acute toxicity usually occurs within a half hour to four hours after consuming toxic levels, and the onset of symptoms is rapid. Symptoms include: rapid/difficult breathing; noisy breathing; weakness; coma and death; salivation; bloat, tremors and staggering; bluish/chocolate brown mucous membranes; and dark chocolate-colored blood.

Chronic poisoning, which are sublethal doses, may still result in abortions, weight loss, reduced milk production and other animal performance issues. If a pregnant female survives nitrate poisoning, abortions generally occur approximately 10 to 14 days following exposure to nitrates.

The typical culprit for nitrate toxicity is cereal grains – oat, Sudangrass, rye, wheat, barley, triticale, spelt, etc. – that are baled or grazed. However, toxicity has been reported in other crops such as bromegrass, orchardgrass, fesuces, sorghum, millet, corn, sweet clover and alfalfa. Specific weed species can also be of concern. These include kochia, lambsquarter, pigweed, quackgrass and Russian thistle.  

Nitrate accumulations within forages

The uptake of nitrates from the soil is a normal and natural process for plants to obtain the nitrogen requirements needed for growth and development during the growing season. Nitrate accumulation occurs when roots accumulate nitrate faster than the plant can convert it into protein. This typically is correlated with the stage of plant growth and/or enhanced by specific conditions, most commonly climatic conditions. 

The highest levels of nitrate are found in the lower one-third of the stem and in vegetative growth stages. Under normal conditions, nitrate levels are consumed as the plant matures further into grain development.

 As for specific conditions, the most common event is drought. However, frost periods, unseasonable cool weather patterns, hail, shade, disease and insect pressures, herbicide damage and grazing during the growing season can also stress the plant into accumulating more nitrates. 

Conditions to be aware of, especially with cereal grains, would be crops – including grass pastures and hay – grown on soils with high manure applications, high-nitrogen fertilizer applications or under stress conditions like drought.

 Unfortunately, nitrate toxicity is so unpredictable that it can even occur in normal growing conditions.

Managing to reduce risk

There are a few management practices producers can enlist to protect livestock against the risk of nitrate poisoning, but keep from wasting forage that may have high-nitrate levels. 

Ensiling forages is the safest and most effective way to manage high nitrate levels. During the fermentation process of silage, the microbial activity consumes the nitrates resulting in a 10 to 60 percent decrease in nitrate levels.  

Another option would be delaying the harvest of the forages to later maturity stages, for example, from flowering to soft-dough stage. One questionable option is raising a cutter bar to only harvest the top two-thirds of the hay. 

For forages that have experienced environmental events, such as cool weather, hail, pest pressures, drought, etc., it is recommended to always test for nitrate levels prior to grazing or haying.

As hay is purchased this fall and winter, do not be afraid to request a forage analysis for nitrate toxicity – especially on cereal grain forages. Also, as plans are being made for next year’s forage crops and grazing rotations, keep in mind nitrate toxicity and ways to minimize risk.  

For more information on nitrate toxicity symptoms in livestock and for treatment, contact a local Extension office.

Jeremiah Vardiman is a University of Wyoming Agriculture and Horticulture Extension educator. He can be reached at jvardima@uwyo.edu.