Nitrate poisoning is generally caused when animals eat too much forage that is high in nitrates not changed to protein in the plant. Poisoning can also happen when animals eat too much urea or nitrogen fertilizer spilled in the field or left where the animals can find it. Nitrate fertilizer is palatable, especially to cattle

Barao, Scott M.

Cassel, E. Kim

Vough, Lester R.

English

Public Research Access Institutional Repository and Information Exchange

South Dakota State UniversityOpen PRAIRIE: Open Public Research Access InstitutionalRepository and Information ExchangeExtension Extra SDSU Extension1-1-2006Nitrate Poisoning of Livestock Causes andPreventionLester R. VoughSouth Dakota State UniversityE. Kim CasselSouth Dakota State UniversityScott M. BaraoSouth Dakota State UniversityFollow this and additional works at: http://openprairie.sdstate.edu/extension_extraThis Other is brought to you for free and open access by the SDSU Extension at Open PRAIRIE: Open Public Research Access InstitutionalRepository and Information Exchange. It has been accepted for inclusion in Extension Extra by an authorized administrator of Open PRAIRIE: OpenPublic Research Access Institutional Repository and Information Exchange. For more information, please contact michael.biondo@sdstate.edu.Recommended CitationVough, Lester R.; Cassel, E. Kim; and Barao, Scott M., "Nitrate Poisoning of Livestock Causes and Prevention" (2006). Extension Extra. Paper 114.http://openprairie.sdstate.edu/extension_extra/114ExEx 4015Dairy ScienceNitrate Poisoning of Livestock Causes and PreventionLester R. Vough, Extension forage crops specialist,Department of Natural Resource Sciences and Landscape Architecture, University of MarylandE. Kim Cassel, information resource management specialistSouth Dakota Cooperative Extension ServiceScott M. Barao, Extension livestock specialist,Department of Animal and Avian Sciences, University of MarylandNitrate poisoning is generally caused when animals eat too muchforage that is high in nitrates not changed to protein in the plant.Poisoning can also happen when animals eat too much urea ornitrogen fertilizer spilled in the field or left where the animalscan find it.  Nitrate fertilizer is palatable, especially to cattle.Causes of High Nitrates in ForageAll plants contain some nitrate, but excessively high levels arelikely to occur in forages grown under stress conditions, such aswhen corn fertilized for high grain yield is stunted by droughtand is alternatively harvested for silage.  Other plants such as sudangrass, sorghum, pearlmillet, oats,orchardgrass, and tall fescue can also accumulate nitrates at highlevels.  Most weeds commonly found in corn also accumulatetoxic levels of nitrate; they include red root pigweed, commonlambsquarters, ragweed, velvetleaf, witchgrass, Canada thistle,and black nighshade.Nitrates accumulate in plants only when 1)  there is a largeamount of nitrate in the soil, or 2)  some factor interferes withnormal plant growth.  High rates of nitrogen fertilization and drought conditions arethe most important factors contributing to nitrate buildup inplants.  Generally there is a direct response in plant nitrate con-centration to increasing fertilizer nitrogen.  Nitrate accumulationis greater from nitrate fertilizers than from ammonium sulfate orurea and also greater with delayed applications of fertilizer.The highest levels of nitrate accumulate when drought occursduring heavy nitrate uptake by the plant.  A drought during orimmediately after pollination is often associated with the highestaccumulation of nitrates.  Extended drought prior to pollinationis not necessarily a prelude to high accumulations of nitrate.  The resumption of normal plant growth after a heavy rainfallwill reduce nitrate accumulation in corn plants, and harvestshould be delayed for 3 to 4 days after the rain.Nitrates absorbed by plant roots are normally incorporated intoplant tissue as amino acids, proteins, and other nitrogenous com-pounds.  Thus, the concentration of nitrate in the plant is usuallylow.  The primary site for converting nitrates to these products isin growing green leaves.  Under unfavorable growing condi-tions, especially drought, this conversion process is retarded,causing the nitrate to accumulate in the stalks, stems, and otherconductive tissue.  Highest concentration of nitrate is in the lower part of the stalkor stem.  For example, the bulk of the nitrate in drought-strickencorn plants can be found in the bottom third of the stalk (Table1).  If moisture conditions improve, the conversion processaccelerates, and within a few days nitrate levels in the plantreturn to normal.C o l l e g e  o f  A g r i c u l t u r e  &  B i o l o g i c a l  S c i e n c e s  /  U S D ANot all drought conditions cause high nitrate levels in plants.  Ifthe supply of soil nitrates is in the dry soil surface, plant rootswill not absorb nitrates.  Some soil moisture is necessary fortheir absorption and accumulation.Nitrate Toxicity in the AnimalLike plants, ruminant animals also use the nitrogen in nitrates tomake protein.  Conversion is made by bacteria in the rumen.Nitrite, one of the intermediate products in this conversion, isthe cause of nitrate poisoning.  Nitrate toxicity occurs whenhigh nitrate levels in the feed overwhelm the animal’s digestivesystem to the extent that the rate of conversion of nitrate tonitrite is faster than the conversion of nitrite to ammonia (whichis incorporated into amino acids and protein).  When this hap-pens, nitrite accumulates and is absorbed into the bloodstream.There, it reacts with the oxygen-carrying hemoglobin, changingit into a form (methemoglobin) that cannot transport oxygen tothe lungs and body tissues.  The animal literally suffocates.Cattle are much more likely to be affected than sheep or horses.The toxicity level depends both on how much and how fastnitrate is consumed.  For example, it takes about twice as muchnitrate to kill a ruminant when nitrate is eaten in forage as whenit is consumed quickly as in a supplement or accidental con-sumption of nitrate fertilizer.  In the case of forage, toxicity gen-erally occurs when cattle consume large amounts of forage con-taining 1.76% or more nitrate ion on a dry matter basis.  Even forage with lower lev-els of nitrate may adverselyaffect reproduction orbecome toxic if animals arenutritionally stressed or illand they suddenly consumelarge quantities of the forage.The recommended uses forforages containing variouslevels of nitrate are listed in Table 2.  A high level ofnitrate or nitrite in drinkingwater may make it necessaryto further reduce intake of nitrate-containing forage.  A totalintake of 30 to 45 grams of nitrate ion per 100 pounds of bodyweight is considered acutely toxic in normal animals.  However,intakes of 8 to 22 grams per 100 pounds of body weight may betoxic when animals are ill or undergoing an abrupt diet change.Symptoms of nitrate poisoning appear suddenly.  Dyspnea (dif-ficult breathing) becomes progressively more severe until signsof marked respiratory distress—mouth breathing, violent respi-ratory movements, and extreme apprehension—are observed.  Arapid and weak heart beat, below normal body temperature,muscular weakness, loss of muscular coordination (staggeringgait and muscular tremors), blue coloration of mucous mem-branes, and marked dilation of pupils follow initial observedTable 1.  Nitrate nitrogen in 28 samples of drought-stressed corn.Plant part                    ppm NO3N1Leaves   64Ears   17Upper 1/3 of stalk   153Middle 1/3 of stalk   803Lower 1/3 of stalk   5,524Whole plant   9781 ppm = parts per millionSource:  University of WisconsinTable 2.  Guide for nitrate levels in forages for mature cattle.1Percentage nitrate ion               Content of nitrate(NO3-)                                  nitrogen(dry matter basis)                   (dry matter basis)                                                              Comments2percentage                 ppm3  less than 0.44        0.0 - 0.10               0 - 1,000       Safe to feed if adequate feed and water are available.   0.44 - 0.66 0.1 - 0.15 1,000 - 1,500 Safe for nonpregnant animals.  Limit to 50% of total ration dry matter for pregnant animals; animals may go off feed, have a slow drop in production, some abortions are possible.0.66 - 0.88 0.15 - 0.20 1,500 - 2,000 Limit to 50% of total ration dry matter for all animals; may experience some symptoms, possibly death.0.88 - 1.54 0.20 - 0.35 2.000 - 3,500 Limit to 35 to 40% total ration dry matter.  Do not feed to pregnant animals.1.54 - 1.76 0.35 - 0.40 3,500 - 4,000 Limit to 25% total ration dry matter.  Do not feed to pregnant animals.  greater than       greater than        greater than  Toxic.  DO NOT FEED.1.76                    0.40                 4,0001 Table partially adopted from August 25, 1970, Hoard’s Dairyman, Fort Atkinson, Wisc:  W.D. Hoard & Sons Co.2 Total ration dry matter refers to total dry matter being consumed as forages and concentrates.3 ppm = parts per million2symptoms.  Brownish discoloration of the blood is characteristicof nitrate poisoning.  Death may occur within 1 hour or, in theusual case, within 3 to 4 hours of the onset of difficult breathing.Subacute or chronic nitrate poisoning may result in reproductiveproblems, including abortions.  Abortions due to nitrate are usu-ally accompanied or preceded by some evidence of nitrate poi-soning in the animals, including bluish discoloration of unpig-mented areas of the skin or mucous membranes.  Poisoning symptoms that precede abortions may be missed ifanimals are not being closely observed, since the abortions willoccur several days after the animal consumes the nitrate.Milk production and appetite generally are not affected by sub-acute nitrate intake.  Reproductive problems may be prevented ifnitrate-containing feeds are gradually introduced into the dietand the nitrate level in the total ration dry matter is maintainedbelow 1.76%.Treatment: If you suspect nitrate poisoning, call your veteri-narian immediately.  Since death comes from oxygen deficiency,cattle should be handled as little and as quietly as possible tominimize oxygen usage.  Administration of a 2% solution ofmethylene blue by your veterinarian aids in the reconversion ofmethemoglobin to hemoglobin, increasing the oxygen carryingcapacity of the blood and reversing the poisoning process.  This treatment may need to be repeated since absorption ofnitrate will continue from a full rumen.  Mineral oil or mucilagi-nous substances may be given orally to protect irritated mucousmembranes, help reduce the absorption of nitrates, and aid intheir elimination.Reducing the Threat of Nitrate ToxicityIf growing conditions favor the accumulation of nitrate in for-age, the following management practices will greatly reduce thechances of problems occurring:1. Consider ensiling the forage; this will reduce nitrate levels.Studies at Purdue University showed that ensiling corn foragereduced nitrate concentration by about one third (Table 3).Feeding should be delayed until the fermentation process iscomplete.  This usually takes about 4 weeks.  Purdue studieshave also shown that adding 20 pounds of limestone per ton ofsilage going into the silo further reduced nitrate levels.  Addingmore than 20 pounds per ton adversely affected fermentationand quality of the silage.  Limestone tends to raise the pHwhich, in turn, can reduce silage quality.Nitrate levels in silage also can be reduced by chopping the toptwo thirds of the plant, since nitrate accumulation is highest inthe bottom third of the stalk or stem.  Leaving that much of theplant in the field is often a difficult decision but it may be lesscostly than the possible loss of animals.  Stalks left in the fieldcan be a source of nitrogen for next year’s crop.Ensile at the proper moisture content (60 to 68%), chop clean,and pack well.  Proper ensiling procedures improve the fermen-tation process and help to reduce nitrate levels.  Application ofanhydrous ammonia to drought-stricken corn is not recommend-ed.  The additional nitrogen has potential to impede breakdownof nitrates in the rumen, particularly if ration energy is limited.2.  Before feeding the forage, have it chemically analyzed fornitrate content.  A complete feed analysis is advisable becausedrought-stressed forages tend to have higher protein content andreduced levels of total digestible nutrients (TDN) or energy.  When sampling suspected silages or greenchop for nitrates, takerepresentative grab samples from six areas at the feeding face ofthe pit or mound.  Mix the grab samples and sub-sample anamount to fill a plastic bag that can be sealed at the top.Compress or squeeze the air out of the bag and seal.For suspected forages being ensiled in an upright silo, take grabsamples for three days in a row.  Keep samples in an airtightcontainer in a cool location.  On the third day, mix the samplesand follow procedures described above.Table 3.  Effect of ensiling on nitrate concentration in cornsilage.Nitrogen applied (lb/acre)Corn fed as                                 0                200                800Green forage  Nitrate (ppm1) 602 2,319 4,438Silage Nitrate (ppm)    380    1,468    2,861Decrease with ensilingpercentage   37    41    36pH   3.9    3.8   3.81 ppm = parts per million.  Nitrate values on dry basis.  To convert val-ues from ppm to percentage, move the decimal point four paces left;for example, 602 ppm = .06%.Source:  Purdue University3Suspect long hay should be sampled with a hay probe.  Forbaled hay, probe at least 20 different bales; and for hay stacks,sample each stack in six different areas to obtain a representativesample.  Transfer samples to a plastic bag, squeeze the air out,and seal.  It is difficult, if not impossible, to obtain a representative samplefrom pastures/fields suspected of high nitrates.  Cattle are selec-tive in the plants and plant parts they choose to eat, and aclipped sample will not represent what is actually being con-sumed.  It is recommended you not test grazed forages fornitrate but that, if you choose to graze, you manage the grazingof such forages to reduce potential nitrate problems.  Recognizeyou are managing risk.  3.  Dilute known high nitrate feeds with low nitrate feeds, such asgrain or legume hay, to reduce the percentage of nitrate in thedaily ration.  Grain feeding seems to be helpful in diluting thenitrate content of the feed.  Energy from the grain helps to com-plete the conversion of nitrate to ammonia, which is then used byrumen bacteria to make bacterial protein.  Corn forage is normal-ly a high-energy feed that favors the use of nitrate in the rumen.Sudangrass, on the other hand, is a low-energy feed which, byitself, does not promote the conversion of nitrate to ammonia.4.  Frequent intake of small amounts of high nitrate feed increas-es the total amount of nitrate that can be consumed daily withouttoxic effects.  Feed limited amounts several times daily rather thanlarge amounts once or twice daily.  With frequent intake of limit-ed amounts of high nitrate feed, concentration of nitrate in therumen does not become extremely high at any one time.Feeding frequency and grain feeding recommendations to reducethe risk of nitrate toxicity refer primarily to milking cows.  Useextreme caution if bred heifers or dry cows must be fed feedscontaining greater than 0.44% nitrate ions.  Typically these ani-mals are not fed more than once daily, nor are they fed largequantities of grain, the primary ways to prevent toxicity if highnitrate feeds are fed.  Young heifers should not be given feedsthat are not safe for all livestock to consume.5.  Introduce questionable feed slowly over a period of a weekor two so that the rumen bacteria can adapt.  All sound manage-ment practices that are conducive to a successful feeding pro-gram should be followed when high nitrate feeds are fed.  In Purdue University experiments, when green corn with 2.29%nitrate was fed to unadapted steers, nitrate in the rumen fluidincreased measurably within 1 to 1 1/2 hours after feeding.However, each succeeding day the nitrate levels were lower anddid not increase again when the experimental forages were fedto the now-adapted animals.6.  Be sure that the ration is balanced.  A balanced ration thatprovides needed nutrients will tend to reduce problems fromnitrates in the ration.  Rations should be adequate in vitamin A,vitamin E, and all minerals.  Excessive supplementation does notappear to be necessary.Nitrates in WaterMost well water is lower in nitrates than the maximum 10 partsper million (ppm) nitrate nitrogen (NO3N) that is suggested asbeing safe for adult humans and mature livestock.  Infants andimmature ruminants are susceptible to nitrate toxicity whenwater exceeds 10 ppm NO3N.When livestock are drinking well water, nitrate toxicity resultingfrom the water is not likely to occur.  Nitrate toxicity from wateris most likely to occur when livestock drink water from ponds,road ditches, or other surface impressions that collect drainagefrom poultry houses, feedlots, heavily fertilized fields, silos, sep-tic tanks, or manure disposal lagoons.As with feed, frequent intake of water appears to increase thetotal amount of nitrate that can be consumed daily without harm-ful effects.  Conversely, water consumption limited to only oncedaily will reduce the level of tolerable nitrates in water beforepoisoning symptoms appear.From the information currently available it is difficult to set amaximum nitrate content for water that should be consideredsafe for mature livestock.  Most data tend to suggest toxicity isnot likely to occur in water containing less than 100 ppm NO3N,provided that animals are fed a balanced ration that is not highin nitrate and that sound feeding, watering, and managementpractices are followed. However, a high level of nitrate in the water can become criticaland will contribute to toxicity when nitrate levels in foragesapproach 1.76%.This publication and others can be accessed electronically from theSDSU College of Agriculture & Biological Sciences publications page http://agbiopubs.sdstate.edu/articles/ExEx4015.pdfor from the Extension Service Drought Information Websitehttp://sdces.sdstate.edu/drought/4South Dakota State University, South Dakota counties, and U.S. Department ofAgriculture cooperating.  South Dakota State University is an AffirmativeAction/Equal Opportunity Employer and offers all benefits, services, education,and employment opportunities without regard for race, color, creed, religion,national origin, ancestry, citizenship, age, gender, sexual orientation, disability,or Vietnam Era veteran status.  ExEx4015, 2006.

Nitrate Poisoning of Livestock Causes and Prevention

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Nitrate Poisoning of Livestock Causes and Prevention

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