How to Treat and Prevent Nitrate Toxicity in Cattle

Nitrate toxicity or nitrate poisoning is a condition where excess nitrates in feeds creates a dangerous condition in ruminants like cattle that can cause them to have a lack of oxygen in the bloodstream. Death is a result if not caught and treated immediately.

Treatment of nitrate poisoning is possible, but it's much harder to catch animals with nitrate toxicity symptoms than it is to prevent the situation from happening. This article particularly stresses the importance of preventing nitrates from accumulating in the feed, from the field to the feeder.

Part 1
Part 1 of 3:

Learn About Nitrate Toxicity

  1. Nitrate toxicity is basically a form of "anti-quality factor" that is associated with animals consuming plants that have a substance that creates health issues in them, just like with bloat is an anti-quality factor, or sweet clover poisoning, or grass/winter tetany. With nitrate toxicity, plants have to be injured by frost, hail, drought, or even sudden cool and cloudy weather conditions and grazed when the nitrate levels have reached excess to what the animals can tolerate. These plants have to be either grazed or harvested in order to have a negative effect on livestock, particularly ruminants like cattle.
    • Nitrate toxicity or poisoning occurs mainly in ruminant animals. When animals consume feed containing excess nitrates (NO 3 - ), they are converted into nitrites (NO 2 - ) by rumen bacteria. These nitrites cross the rumen wall and enter the bloodstream, combining with hemoglobin to form methemoglobin to interfere with the red blood cell's capacity to carry oxygen to body tissues.
      • Normally nitrites, when nitrates are at low levels in the feed, are converted into ammonia by bacteria, which is a detoxification process because nitrites are 10 times more toxic than nitrates. This detoxification occurs more slowly than the conversion of nitrate to nitrite.
        • When the microbial capacity to convert nitrite to ammonia is overwhelmed by the higher nitrite level in the rumen, initial development of poisoning will occur. Nitrates and nitrites cross into the rumen wall and interfere with the iron ions of the red blood cells.
          • The ferrous iron of hemoglobin converts into the ferric form, thus forming methemoglobin. Methemoglobin does not have the same oxygen carrying capacity as hemoglobin, thus tissues do not get enough oxygen and begin to suffer from oxygen starvation.
      • The change in hemoglobin in the red blood cells are affected by four main criteria:
        • The rate of nitrate intake (how much nitrate is in the feed and how quickly it gets consumed);
        • The rate of conversion of nitrite into ammonia in the rumen (or lack thereof);
        • The rate of digestion of feeds and the subsequent release of nitrates (which tends to occur in a positive feedback loop);
        • The movement of nitrites out of the rumen via feed passage rate (how quickly the feed, and the nitrates in it, enters the rumen).
      • A positive feedback loop occurs if the animals continuously have access to high nitrate-feed. While nitrates in the bloodstream–which do not create toxicity problems initially–can get recycled back into the rumen via saliva or intestinal secretions, and get converted into nitrites, high nitrate feeds exacerbate the problems because nitrates are continually being flooded into the system and either rapidly converted into nitrites in the rumen, or enter the bloodstream to be recycled back into the rumen again and reabsorbed into the blood as nitrites.
  2. Basically, there has to be a large application of nitrogen-based fertilizer (urea, anhydrous ammonia, ammonium nitrate [extremely difficult to purchase, and illegal for use in some countries], mono-ammonium phosphate, and others) or manure (primarily from horses, cattle, or pigs [1] ) to the field to increase soil nitrogen (nitrate) content and thus increase nitrate availability to the plant. When there is a high soil nitrate concentration, surplus quantities of nitrates are taken up by the plant, where accumulation occurs.
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  3. A plant's metabolic activity level will influence how much nitrate is used by that plant. Nitrate will combine with carbohydrates during a plant's metabolic processes to form amino acids glutamine and asparagine. Both amino acids are the base units for all other plant amino acids and subsequent proteins. Nitrate brought into the plant accumulates in the stems and leaves when glutamine and asparagine pathways become saturated. Plant enzymes require nearly perfect conditions in order to function at or near maximum capacity. The pathway of nitrate-utilization depends on 1) adequate water supply, 2) energy from sunlight, and 3) warm temperatures. If any or all aforementioned conditions are not ideal, the rate of conversion for nitrate to become amino acids is impaired; the plant uses up all its available sugars, thus resulting in accumulation of available soluble nitrogen as nitrate and ammonia.
    • Plants accumulate nitrates from the soil through the roots up into the plant. Young, growing plants are more likely to store more nitrates in their stems and leaves (or rather, throughout the entire plant) than with mature plants. Most nitrate accumulation in mature plants occurs in the bottom third of the stem; almost none are found in the top of the plant, like in the grains or fruits, making any grains and seeds nitrate-free.
  4. Any time that plants become stressed, as in drought or with hot dry winds, when they become damaged by frost or hail, or even cool cloudy weather conditions, are most likely to accumulate nitrates. Basically, anytime a plant's photosynthetic capacity is compromised or impaired, nitrates are prone to accumulate to excessive levels.
    • Roots are unaffected by most climatic events, so they are going to be pumping up the same amount of nitrates into the rest of the plant as they would if the plant wasn't injured or compromised. This is what gives rise to excess nitrates after a plant is stressed and/or injured.
    • The highest nitrate accumulation levels don't peak immediately after being injured by hail or frost, but rather 4 to 5 days afterwards. Safe harvest times are the first two days after, or 10 to 14 days later.
      • Prussic acid can be confused with nitrates because it too is an anti-quality factor, mainly associated with warm-season grasses. However, prussic acid peaking times are different from nitrates in that they peak immediately after a plant feels stressed where photosynthesis is impaired, and go back to normal levels two weeks after.
  5. Several cultivated crop species and weed species are commonly known as nitrate accumulators.
    • Cultivated crop plants :
      • Barley (as greenfeed)
      • Oats (as greenfeed)
      • Wheat (as greenfeed)
      • Corn (standing grazing)
      • Rye (as greenfeed)
      • Triticale (as greenfeed)
      • Sorghum (standing crop for grazing; prussic acid also a problem)
      • Sorghum-sudan grass (standing crop for grazing; prussic acid also a problem)
      • Johnson grass
      • Sudan grass
      • Millet (most species/cultivars)
      • Tall Fescue
      • Crabgrass
      • Bermuda grass
      • Rescue grass
      • Rye grasses
      • Beet tops
      • Flax
      • Canola plants
    • Weed plants are :
      • Bull Thistle
      • Russian Thistle
      • Canada Thistle
      • Kochia
      • Lambs quarters
      • Mustards
      • Pigweed
      • Smartweed
      • Wild Sunflower
      • Firewood
      • Nightshade
      • Jimsonweed
      • Careless weed
      • White Ragweed
      • Dock
      • Cud weed 
      • Horse nettle
    • Pasture plants, and all legumes (cultivated crops and perennial forage) including alfalfa are significantly low to non-risk for nitrate accumulation. Most pastures are not fertilized heavily enough or see excessive amounts of manure to pose a nitrate toxicity risk. However, the risks shouldn't be ignored especially if pastures are grazed or managed so that they see plenty of manure (at least 50 lb per acre) being deposited annually.
    • Access to nitrogen-based fertilizers can also induce onset of nitrate toxicity, or urea/ammonia poisoning.
      • With the latter type poisoning, blood ammonia levels are the major cause of toxicity issues, not methemoglobin levels. Ammonia prevents carbon dioxide from being released by red blood cells. Symptoms include dehydration, abnormally high body temperatures, laboured breathing, muscle tremors, appearance of sunken eyes and looser-than-normal skin, and a fluid-filled rumen.
        • Drenching 4 L of vinegar into a mature cow every 20 to 30 minutes until the symptoms disappear is the best antidote for urea or ammonia poisoning.
  6. Sheep, goats, bison, elk, deer, and other ruminants are as likely to suffer from nitrate poisoning as cattle are. All classes of cattle, regardless of gender, age, production stage or type, are equally likely to suffer or perish from nitrate toxicity.
    • Sheep are the least sensitive to nitrate poisoning compared with cattle, which are the most sensitive. Sheep are more adapted to converting methemoglobin to hemoglobin, and nitrite to ammonia than cattle are, which is why they can be fed feeds that are higher in nitrate content.
    • Monogastric animals like horses and pigs are much less likely to be affected by nitrate toxicity because nitrates are converted to nitrites primarily in the intestine, which is closer to the end of the digestive tract making for reduced opportunity for nitrites to become absorbed into the bloodstream. However, nitrate toxicity in these animals is still a risk, but not nearly as significant as in ruminants.
  7. Feed containing 0.5% nitrates or less is generally safe for ruminants. Recent research, though has discovered that cows have had no adverse effects if nitrate levels are between 0.5 and 1%. However, subclinical or chronic nitrate toxicity can develop when levels get between 0.5 and 1% so you need to be cautious when feeding out feeds that contain these nitrate levels, especially with animals that have not become acclimatized to nitrates that are above even 0.5%.
    • If you are interpreting two other test methods besides the percent of nitrates (as %NO 3 ), such as Nitrogen Nitrate (%NO 3 -N) or Potassium Nitrate (%K-NO 3 ), then the values are slightly different. The maximum allowable %NO 3 -N is 0.23%; safe levels are 0.12% or less. Between these two values, you must be cautious with feeding nitrate-heavy feed. Maximum allowable %K-NO 3 is at 1.63%; safe levels are at 0.81% or less. Like with nitrogen nitrate, you must be cautious with feeding any feed that comes back with %K-NO 3 levels between 0.81% and 1.63%.
    • The dangers with nitrates exist especially when animals are not acclimatized to being on such feeds. When animals are slowly introduced over time, they can slowly become acclimatized to eating feed that is even at least 1%, but the thing that must be remembered is very slow introductions to such high-nitrate-containing feed!
  8. Acute toxicity signs and symptoms include rapid and weak heart-beat, subnormal body temperature, muscular tremors, weakness and ataxia (as in staggered gait, disorientation, etc.). Brown/bluish-grey mucous membranes, excessive saliva and tear production, laboured and rapid breathing, frequent urination, as well as vomiting (more common in monogastric animals), diarrhea or scouring, and an inability to get back up from laying down are also frequent. Death soon follows within a few hours after animals have been fed.
    • The main cause of death is via asphyxiation with a lack of oxygen being supplied to bodily tissues.
    • Subacute nitrate toxicity is often corresponding with abortions, reduced weight gain, reduced feed intake, reduced milk production, increased susceptibility to illness and infections, and reproductive problems such as silent heats and reduced fertility. Often signs and symptoms of subclinical or chronic nitrate toxicity go unnoticed or are not related to feed quality.
      • Animals can go without showing signs of distress for several days to several weeks while consuming nitrate-containing feedstuffs. By this time they can appear belligerent, uncoordinated (especially hind-quarters), develop diarrhea, eye lesions, and symptoms similar to pneumonia, such as interstitial pulmonary emphysema (fluid accumulating in the lungs). Prolonged exposure to nitrate-containing feeds coupled with cold stress and poor nutrition can lead to downer cow syndrome [2] .
        • At this time, cows are also likely to abort or give birth to stillborn calves, regardless of the stage of pregnancy they are in.
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Part 2
Part 2 of 3:

Treating Nitrate Poisoned Cattle

  1. Understand first that nitrate poisoning affects the system very quickly, so much that you may not be able to catch affected animals in time. The section above has already mentioned that feeds with high nitrate levels (above 1% NO 3 ) can kill an animal in a matter of 2 to 3 hours after feeding. With beef producers who only see their animals once a day or once every few days, the only symptom that producers can go off of to tell if their animals have nitrate poisoning is if they have dead animals. Dairy producers are more likely to catch their cows before it's too late
  2. When animals are exhibiting signs of laboured, rapid breathing, bluish-grey mucous membranes (lips, tongue, and nose), weakness, rapid and weak heart rate, lethargy/depression, excessive salivation and tear production, and a staggered gait and disorientation, you may have animals with nitrate toxicity on your hands.
    • As mentioned above, you may be feeding feeds that have nitrates that are less than 1% as tested, and may not see any symptoms develop until days or weeks after the start of feeding that nitrate-containing feed to your animals.
  3. Keeping them on that nitrate is only exacerbating the problem, not solving it. Removing them from the feed will help get the nitrates and nitrites eventually out of their system, allowing the microbes in their rumen to catch up to converting the nitrites to slightly less harmless ammonia and urea.
  4. They will need to come out to assess and confirm that you indeed have animals with nitrate poisoning, and if you have dead livestock, to perform necropsy/autopsy on them.
  5. This is a very dangerous situation because the nitrites in the system are already taking up valuable oxygen, making it difficult for the animal to breathe. If the animal is pushed too hard, this could cause a "downer cow" situation that needs to be remedied faster than ever. Move them easy and slowly, and let them take their time to get them where you want to go.
    • Do not move any downer animals, as this will also cause more stress to their system than they're already going through with the bad feed.
  6. inject a 1% (or 4%) solution of methylene blue into the vein ( intravenously ) of the affected cow [3] . Methylene blue needs to be mixed with distilled water or isotonic saline to be effective, and should be given at a dose of 4 to 22 mg/kg or more (or 0.004 to 0.022 cc per kg of body weight (if using pounds, remember 1 kg = 2.205 lb)), depending on the severity of poisoning. Lower dosages may be repeated in 20–30 minutes if the initial response is unsatisfactory. If additional exposure or absorption occurs during treatment, re-treat with methylene blue every 6 to 8 hours must be considered. Rumen cleansing (via drenching or tubing) with cold water and antibiotics may curb the continuous microbial production of nitrite.
    • The lower dosages of methylene blue can be used in all species, but only ruminants can safely tolerate higher dosages.
  7. But keep the animal in a smaller corral so that you can keep an eye on it, and others that have been treated, for the next 24 hours or so.
  8. While doing so, severely limit how much they get daily, and feed another nitrate-feed for the time being.
  9. Keep the your stock off the affected feed until you can figure out the best solution to limit-feed it without causing significant issues. You may need to re-test your feed, or purchase additional feed to hold them over for the rest of the winter.
    • Cows can become acclimated to high-nitrate feeds, but only if they are introduced to the forage slowly over a few weeks at a time.
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Part 3
Part 3 of 3:

Preventing Nitrate Poisoning

  1. As already mentioned in the "Learning About Nitrate Toxicity" part above, nitrate accumulation happens anytime a plant feels stressed and when photosynthetic capacity is impaired. The highest risk for nitrate accumulation occurs when plants are stressed or damaged by hail, frost, or drought. Less often, except in warmer locations, will excess nitrate accumulation be more often associated with damp weather and cool temperatures (at 55ºF [13ºC]).
    • Nitrates are always going to peak a week (or around 5 days) after being injured, before returning to normal levels 10 to 14 days after which the injury occur.
  2. Time harvest according to environmental influences to get feed that is low in nitrates and possesses the lowest possible nitrate toxicity risk. As mentioned already, nitrates are not going to peak immediately after the event their photosynthetic abilities become compromised, so a narrow window to harvest or graze occurs immediately after the frost or hail event. This window is generally only 1 to 2 days long. After that, do not harvest nor graze until two weeks after the event has passed.
    • If you decide to wait a week after, you will instead target a time when nitrates are going to be at their peak and at the most dangerous levels for your animals.
      • It is an opposite story with plants that are also affected by prussic acid levels; Prussic acid will peak immediately after a frost, hail, very hot or suddenly cool weather event, and go back to normal after a week.
        • Warm-season grasses like bermuda grass, sorghum, sorghum-sudan and others are the greatest risk for prussic acid poisoning to livestock.
    • Frost events can be tricky with regards to nitrate accumulation. A light frost (-1 to -4ºC) will allow plant tissues to recover, but killing frost (-5ºC or lower) will outright kill a plant. The trick to remember with killing frosts is that if they occur a week after the latest light frost, nitrates are going to be "locked in" to the plant material, or stay put in the plant material no matter how much time has passed. However, if a killing frost occurs two weeks after the last light frost, then the nitrate risk is going to be low to non-existent because the plant material will be dead, so much that nitrates are not likely to accumulate in the tissues.
      • Nothing can be done to the plants if a killing frost occurs a week after the last light frost, because the nitrates are going to be there in the dead plant tissues. Same thing with harvesting; if you've harvested forage with potential for nitrate accumulation a week after a hail or frost, you will be ending up with feed material with higher nitrates than what your animals, if unacclimatized, could handle.
      • If the killing frost happened two weeks after the last light frost, then you shouldn't have to worry about excess nitrates in the feed. A killing frost destroys plant tissue and membranes so that nothing can be drawn up from the roots; harvesting and grazing can commence for as long as necessary.
        • This is all in a perfect world. Ideally, though, Nature doesn't do what we expect, so precautions should be taken before harvesting or grazing by testing first, or severely limiting the feed until test results come back showing nitrates are at safe levels to increase amount fed.
  3. Crops that have seeded out and are at almost the stage where seeds have matured are less likely to have nitrates throughout the plant than with immature, growing plants. Seeds and fruits have virtually no nitrates in them. Mature plants, however, do have nitrates in the lower one-third of their stem.
  4. When baling up crops for greenfeed, moisture level should be less than 18%, otherwise the bales will heat. Heating exacerbates the nitrate levels, turning the nitrates into nitrites which could make the feed much more toxic.
    • Ensiling crops or even making bale silage will not reduce nitrate levels if the silaging process is done properly. Nitrates will decrease if silage wasn't packed or sealed properly, but this also leads to a decrease in quality in the feed.
      • Crops that are ensiled with a high soluble sugar content (like with cereal grains) undergo a rapid fermentation process. The rapid drop in pH, though, does not promote the rapid degradation of nitrate during ensiling. Rather, the nitrate levels in the silage as it is being stored will either not change or possibly go through some conversion of nitrate to nitrite. It is best to grab samples as the feed is coming to the pit or bunker and send it in to a lab that will test for both nitrates and nitrites.
  5. When manure or nitrogen applications are applied at 50 to 100 or more pounds to the acre, nitrates are more prone to accumulate than if less fertilizer/manure was applied, or even none at all. When nutrients are applied at less than 50, and the crop is harvested at or close to maturity, then there's a chance that the growing crop will have used up most of the nitrates--converted to ammonia, which is used for making amino acids that the plant needs--during growth, and little is left when crops are damaged by frost or late-season hail. However, hail and drought damage earlier when plants are growing will be of more concern during the growing season.
  6. Methods to test depend on the type of feed you have. If you have bales to be tested, use a 36" bale corer. Deeper samples need to be taken if you have a silage pile, at 4 to 5 feet deep. If you are testing standing plants, take 10 to 15 plants from the field in random places, cut them 4" above the ground surface, and bag them up. Taller plants with thick stems will need to be put through a wood-chipper or silage harvester, and gather a collection enough to fill about half a bread-bag or so.
    • Swathed plants make it easier for gathering; just pick several random points in the field to take some plants from and bag them up.
    • If you cannot send a sample in right away, put it in the freezer to keep for longer.
    • Your local fertilizer dealership will know where to send samples for nitrate testing. You can also contact your local ag extension service to find out which local feed-testing laboratories you can send your samples to.
    • As mentioned in the first section above, there are three testing methods for nitrates: %NO 3 , %NO 3 -N, and %K-NO 3 . The 0.5 to 1% levels are from the %NO 3 method. With %NO 3 -N, levels should not go above 0.23%. The method of testing %K-NO 3 dictates that any levels below 1.63% will cause issues. [4]
    • You may also be able to purchase nitrate test strips to use to test your feeds. Normally these strips are used for water, but they can be used on dried-down feed samples that are soaked in water [5] [6]
      • If using reading in terms of mg/kg or ppm, note that 10,000 ppm or 10,000 mg/kg = 1% NO 3 .
  7. You can either send in a sample in a vial that seals up properly, or use nitrate test strips to test the water yourself.
    • Fresh water from the well does not have nearly as significant a risk of nitrate (or rather, nitrite) toxicity problems as with water from dugouts, ponds, depressions, or any water-collecting location that receives runoff from the feedlot area. Certain species of algae growing in water supply can also produce nitrates that may have levels that can be problematic for livestock.
  8. Limit the amount of high-nitrate feed going to cattle, and feed with other non- or low-nitrate feeds in replacement of the high-nitrate feed. How much to limit depends on how heavy in nitrates the feed is and how acclimatized your animals are. If your animals are not acclimatized to high-nitrate feeds, then they will need to be fed nitrate-rich feed at lower levels. For unacclimatized animals (from Midwest Laboratories on Nitrate Toxicity and Nitrate Poisoning in Cattle University of Florida ):
    • 0.0 to 0.3% NO 3 is considered safe to feed under all conditions (frost, hail, drought).
    • 0.3 to 0.6% NO 3 is safe for mature, non-pregnant animals under all conditions, but limit to 50% of total dry matter of ration to pregnant animals and very young animals.
    • 0.6 to 0.9% NO 3 must be limited to 50% or less of the total dry matter in the ration
    • 0.9 to 1.5% NO 3 should limit to 35 to 40% or less of total dry matter in the ration; subclinical affects in unacclimatized animals may be seen in a few weeks (or 6 to 8 weeks) following the start of feeding feeds with this level of nitrate.
    • 1.54 to 1.76% NO 3 should not be used on pregnant animals. Limit to no more than 25% of total dry matter of the ration.
    • 1.76% NO 3 and up should not be fed. Feeds with this amount of nitrate or greater are considered toxic to livestock.
  9. Keeping an eye on the animals when feeding or introducing nitrate-containing feeds will help so that you avoid a potential train-wreck in the future.
    • You may need to improve the mineral program by adding a little more sulphur (at 0.1% of daily ration), and potassium and magnesium to avoid any nutritional problems, and reduce the risk for nitrate poisoning.
    • Have the veterinarian on speed-dial in case of emergencies.
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      Tips

      • Provide a mineral supplement with 0.1% sulphur and magnesium and potassium to counter nitrate issues.
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      • Always have your feed tested if in doubt.
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      • Feeds high in nitrate (of at least 0.5% nitrate) should be limit fed to at least 50% of the total dry matter ration, particularly with pregnant cows and young animals.
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      Warnings

      • Nitrate poisoning is deadly, and can kill livestock. If you do not make effort to remove feed and treat animals showing signs of nitrate poisoning, you will lose animals.
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      References

      1. ↑ Animal Manure as a Plant Nutrient Resource
      2. ↑ http://www.merckvetmanual.com/toxicology/nitrate-and-nitrite-poisoning/overview-of-nitrate-and-nitrite-poisoning
      3. ↑ http://www.merckvetmanual.com/toxicology/nitrate-and-nitrite-poisoning/overview-of-nitrate-and-nitrite-poisoning
      4. ↑ http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex851
      5. ↑ http://extension.oregonstate.edu/douglas/sites/default/files/documents/lf/faqf/nti.pdf
      6. ↑ http://www.uaex.edu/publications/pdf/fsa-3024.pdf
      7. Forage Nitrate Test Kit Instructions
      8. Overview of NItrate and Nitrite Poisoning
      9. [ http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex851
      1. Nitrate Toxicity - UGA

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