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Nitrates

 
      
 
 
 Knowledge Nuggets | Fact Sheets

Knowledge Nuggets

  • Nitrate is the form of nitrogen taken up by the plant roots from the soil. Nitrates are then transported to the stems and leaves. Excess nitrate accumulates in the plant when supply exceeds demand.
  • Damage caused by a sudden heat wave, hail, cool, cloudy weather; or frost impairs photosynthesis, this results in nitrate accumulation in plants. If plants are harvested or grazed after a few days of the stress, the potential for nitrate accumulation increases. If the stress is removed and the plants recover, excess nitrate stored in the plant is metabolized over several days. If there is any concern, test the feed.
  • Immature plants (seedlings during initial growth), take up as much nitrate as possible. At this growth stage, soil nitrogen supply is high and the roots are able to take up more nitrates than the plant requires. Nitrate then accumulates in the stems and leaves. As the plant grows, the leaf mass of the plant increases faster than the root mass, and intake amount matches use. Nitrate supply in the soil decreases during the growing season.
  • Annual forage crops tend to accumulate greater amounts of nitrates than perennial forages. Annual crops are usually planted into well fertilized, manured, or recently plowed grassland or pasture. Annual crops are also harvested at an early stage of development than perennial forages (at milk to dough), when nitrate content is relatively high.
  • Legumes do not store excess nitrates in the plant material. It is stored in the root zone of the plant and is translocated into the plant as required. Alfalfas, vetches, trefoils, peas and clovers generally do not accumulate nitrates.
  • In ruminants, nitrate is converted to nitrite then to ammonia by rumen bacteria. Excess ammonia is filtered by the kidneys and is voided in the urine as urea. This conversion process continues on as long as nitrates and nitrites do not accumulate in the body.
  • Nitrate poisoning occurs when the conversion of nitrate to nitrite exceeds the animals' capacity of converting this nitrite to ammonia. Nitrite causes toxicity by reducing the capability of blood to transport oxygen. Nitrite combines with hemoglobin to form methemoglobin, which is unable to carry oxygen, this causes internal suffocation.
  • Nitrate is continually released from feed digested in the rumen. When nitrate levels in the rumen increase and are not converted to nitrite, nitrate crosses the rumen wall into the bloodstream. Free nitrate from the blood is recycled into saliva. Through rumination, saliva is added to the cud and additional nitrate is returned to the rumen, intensifying the problem.
  • The change in the hemoglobin (red blood cells) is influenced by the following:
    • rate of nitrate intake (amount of feed and how quickly it is consumed)
    • rate of conversion of nitrite to ammonia in the rumen
    • rate of digestion of feeds and the subsequent release of nitrates
    • movement of nitrite out of the rumen
    • quality of feedstuff consumed (heated moist forage vs dry feed)
  • The amount of nitrate being recycled back into the rumen, rate of nitrite breakdown, and diet composition all influence what the "toxic" level of nitrate is for different animals. Individual animals have different levels of tolerance to nitrates / nitrites because of the rates of breakdown and recycling.
Factsheets

Nitrates in Livestock Feed - available in PDF format only

Nitrate Poisoning and Feeding Nitrate Feeds to Livestock

Nitrate Poisoning and Feeding Nitrate Feeds to Livestock Review Paper - available in PDF format only

Nitrate Poisoning of Livestock-Causes and Prevention - available in PDF format only

Nitrate Toxicity - available in PDF format only

Nitrtate Toxicity of Montana Forages

The Merck Veterinary Manual
 
 
 
  For more information about the content of this document, contact Ken Ziegler.
This information published to the web on October 6, 2003.
Last Reviewed/Revised on September 26, 2013.
 

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