Coffman, C.D.

Livingston, S.D.

Paschal, J.C.

OAKTrust Digital Repository (Texas A&M Univ)

Nitrate and aflatoxin poisoning are two problemsencountered with attempts to utilize drought-damaged corn. Under certain unfavorable conditions,each requires special management, handling, orconversion processes before such corn can be fed to livestock. The desire of many growers to redirectdamaged corn fields to silage, greenchop, or pastureshas resulted in livestock death when precautionswere not followed. Likewise, grain produced duringdrought may be contaminated with mycotoxins notencountered under normal growing conditions. Nitrate poisoning is more of a mid- to late-seasonproblem, while field incidence of aflatoxin is usuallyconfined to the end of the growing season, after thesilks turn brown. While nitrate poisoning can alsooccur when livestock have access to nitratefertilizers or contaminated water supplies, thisreport is confined to excess nitrate accumulationsoccurring under drought conditions in grainproducing field crops.Nitrate Accumulation. High rates of nitrogenfertilization often precede outbreaks of nitratepoisoning. Under drought conditions the uptake ofnitrates may exceed the rate of protein synthesis,especially as nitrogen uptake increases as earsapproach silking. High temperatures, large losses of leaf area, failed pollination, limited water uptake,and low phosphate adsorption may each createconditions trapping nitrates in the stalk below theear shoot. Unable to produce enough carbohydrateby photosynthesis to combine with nitrite ions, theseplants have the highest accumulation of nitrates nearthe base of the stalk. If no ear is formed or if earscannot be pollinated, these plants will accumulatethe largest stores of nitrates.With moderation, even this accumulation may betoxic when fed to livestock. The hazard could also beshort-lived if thecorn retains enoughleaves to stay aliveand ears wereformed. If amplerain is received, afew days of normalgrowing conditionswill flush out theaccumulatednitrates and near-normal levels will berestored. But if thecorn is killed bydrought, then thereis no escape for thetrapped nitratesexcept by leaching.Using these plantsas forage becomesincreasingly difficult. Plants which oftenaccumulate nitratesunder drought conditions include field crops,weeds, and vegetables, especially corn, foragesorghums, and grain sorghums.Poisoning Symptoms. The symptoms of acutenitrate poisoning in livestock include staggeringgaits, muscle tremors, rapid pulse and urination,labored breathing and blueing of the mucousmembranes (cyanosis due to lack of oxygen), and abortion (which may occur when acute nitratepoisoning kills the fetus but not the cow). The bloodon post mortem examination will be chocolate-brown in color. Death occurs from asphyxiation. The nitrate ion (NO3) when ingested, is reduced tothe nitrite ion (NO2), which is readily absorbed intoL-5149Preventing Nitrate Problems inDrought-Damaged CornS. D. Livingston, C. D. Coffman, and J. C. Paschal**Professor and Extension Specialist, Agronomy, and Associate Professors and Extension Specialists, Corn and Sorghum, and Livestock, respectively, Texas A&M UniversityTexas Agricultural Extension Service • Zerle L. Carpenter, Director • The Texas A&M University System • College Station, TexasUnable to supply enough carbohydrate tocombine with nitrates from soil-appliedfertilizers, corn plants accumulate nitrogen inthe lower stalk until night temperatures coolenough for photosynthesis proceed.the animal’s circulatory system. The nitrites combinewith the hemoglobin molecule and decrease theoxygen-carrying capacity of the blood. Before harvesting or grazing drought-stressedcorn or sorghum fields, visit with your veterinarianregarding the specific recommendations to follow.The adverse effects of excessive nitrates in livestockare of such a nature that “time is of the essence.”One remedy is an early intravenous injection of 4 milligrams of methylene blue per pound of bodyweight in a 4 percent solution with distilled water.Prevention. Livestock may break into corn fieldsif they are hungry and fences are in poor condition.If possible, herds should be moved to a more securelocation or a hot wire should be installed to protectthe fence. Testing for Nitrates. The diphenylamine quicktest has been used in the field to determine tissuenitrate levels greater than 1 percent. The reagent iscomposed of 0.10 gm of diphenylamine saltdissolved in 30 ml ofsulfuric acid. Whencontained in a bottlewith an eye dropper,the solution can bedribbled onto theexposed pith of splitcorn stalks and thereaction observed.Within seconds, ablue or blue-blackcoloration willdevelop if highamounts of nitratesare present. Fainttinges of blue thatrapidly dissipate areconsidered safe. The test is notquantitative, but itmay be useful todetermine the needfor more accuratetesting at acommerciallaboratory.The plant to be tested should be cut at the soillevel and the stalk split lengthwise, with the exposedpith facing upward. Either place it on the ground orhold it at a 45-degree angle away from you. Allowsome test solution to fill the dropper and let a dropfall on the pith 2 to 3 inches from the base of thestalk. Let another fall about 8 inches up, and placeothers further up the stalk. You will generally findthat the reagent immediately turns dark blue orblack where nitrates are present at levels greaterthan 1 percent. If you split an ear, a leaf midrib, or a tassel, you would probably find only a mild tingeof blue or no color change at all. It is the bottom 12 to 18 inches of stalk that contains most trappednitrates. Consult your local soil or plant tissue testinglaboratories for instructions on nitrate testing,quantities required for sampling, and fees foranalysis. Utilizing Damaged Plants. With pastures fullyused-up and dormant from high temperatures,livestock owners often consider salvaging some feed value fromruined stands ofcorn. The growthstate of the cornmay determine theoption beingconsidered. Fieldsof corn damaged bydrought may havecorn in all stages of development.Emergence is oftenuneven, and theparts of the fieldwith better soilmoisture may bethe only plants toachieve normalplant height or toproduce an ear.Early in drought,leaves begin toyellow and die backfrom the blade tipand edges. Leaves progressively die back from thebottom and up the stalk. Loss of the ear leaf andupper leaves seriously affects grain yields. Belowterraces or shallow slopes or compacted areas, corn may produce a nubbed ear, a barren cob, or a partially filled ear. Remember that nitrateaccumulations are greatest in the lower 12 to 18inches of stalk. Nitrates decline in the proximity ofSplit stalks treated with diphenylaminereveal dark blue or black color changeswhere nitrate levels exceed 1% nitrate.Stalks above demonstrated little or no colorchange, indicating acceptable nitrate levels.Drought stressed corn rolls leaves mid-morning to late afternoon. Progressive leafloss proceeds from bottom to top of plant.the ear, if one is present. Leaves, tassels, and theupper stalk are usually safe from high NO3 levels.The following options and precautions have beenpracticed in drought years. Cattle can be conditioned to eat larger amountsof feed with a higher nitrate content if the increase is gradual. Healthy animals are less likely to beaffected than sick animals. Animals consumingcarbohydrates can tolerate more nitrate. Silage. Unlike prussic acid (which volatilizes in haywith curing), nitrates do not totally dissipate in theensiling process or when plants are left to fielddrying. Some nitrates will be converted to gaseousforms of nitrogen and will escape as silo gas, whileother nitrates will be lost if the silage “runs” andseeps liquid during fermentation. This dischargeshould be considered dangerous and should not be accessible to livestock. Most silage will beacceptable, because 30 to 60 percent of the nitrates are lost in this way. The best silage includes grain as well as foliage.There is a tendency to rush the making of silage,which may be the wrong thing to do. Fields shouldnot be ensiled until dry matter (DM) reaches 28 to 36percent. If corn is ensiled below the 28 DM withoutsufficient earing, there are not enough carbohydratespresent to have proper fermentation, and quite often a putrid silage will develop with excessiveseepage (lost nutrients). When working with uprightsilos, there is always a possibility of accumulationsof nitrogen dioxide or nitrogen tetroxide. These twogases may be recognized by their irritating odor andcolor (reddish brown or yellow). Nitric oxide is acolorless gas that may be present in deadlyconcentrations without visibly being detected. Silage from damaged corn should be tested again for nitrates and fed so as to not provideexcessive amounts. Such silage should beintroduced slowly and modulated with other feedsas needed. Many nitrates can be excluded in theharvesting process by setting the cutter bar high toleave the lower portion of the stalk in the field. Ifplant material is too dry, it may be necessary to add some water to the harvested crop material tomaintain a satisfactory fermentation process and to establish airtight conditions. The rule of thumbwould be to add 4 gallons of water per ton of silagefor each 1 percent desired increase in moisturecontent. This should be added at the time thechopped forage is being put into the trench or silo. Silage requires a minimum of 21 days forfermentation. Pasturage. Putting up hot wires and allowinglivestock to graze the damaged corn (free choice) is more risky, but requires fewer facilities, labor, orequipment. Cattle should have access to good haybefore they are turned into the damaged field. Thispermits a slower introduction to possible nitrates.Many producers have experimentally turned-in oneor two older cows to test the hazards of feedingfrom the damaged field. If no problems areencountered in a reasonable time, the balance of the herd may be brought in. Cattle may selectivelyeat ears, leaves, and tops with less preference forstalks, but this is not always so. Hungry cattle maydevour everything available. Do not turn hungrycattle into suspect fields. Hand-Feeding Greenchop and Cut Stalks. If feed is needed badly, you can select for the betterplants or parts of the field with the lowest nitratelevels. These can be greenchopped for livestockafter spot testing with diphenylamine. Althoughsome plants may test high in nitrates, when mixedwith other plants and plant tops, these levels shouldbe lower. In addition, handcut or greenchoppedstalks can be harvested above the 12- to 15-inch level to avoid the highest nitrate accumulations.Greenchop can be fed in bunks after cattle havebeen fed full of hay. This will also dilute the effect ofindividual plants with high levels. It is the percentageof nitrate in the total ration being consumed that isimportant. The following cautions should beobserved: •Don’t hold green chop overnight or let it heator spoil. A delay in feeding corn forage after it hasbeen chopped will increase the conversion ofnitrates to nitrites by bacterial action. •Don’t feed cattle more than they will eat in afew hours. Start cattle on greenchop slowly. Havecattle full of other feed.•Feed greenchop twice daily. Do not hold second feeding from morning to evening in a wagon.It would be good to feed 5 pounds per head twicedaily for the first few days, then go to 10 pounds perhead twice daily for a few more days and 15 poundsafter 7 to 10 days. Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.Issued in furtherance of cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, incooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.3M—10-95, New AGR 1,6•Supplement greenchop with other feeds tomeet daily nutrient requirements. A mature cowwill need about 4 pounds of corn or about 8 poundsof hay in addition to greenchop to balance minimumneeds. •Do not feed high urea supplements withgreenchop with high nitrates.Baling Stalks in Round Bales. As previouslydiscussed, curing and making rough hay fromdroughted corn does not remove nitrates. Whilethese bales can be an important source ofsupplement to other feeds, they should be tested so that a safe, calculated feeding program canproceed. If such bales are sold to neighbors orstanding corn fields are leased for pasturage,appropriate warnings should be given. Other Plants with Nitrates. Almost any cropplant in the grass family that has received a liberalnitrogen application in a drought year can havepotential nitrate problems. Oats, haygrazers, millet ,and sorghum have each developed problems underthe most unfavorable of conditions. Fall-plantedwheat, oats, rye, and other small grains havenormally escaped the kind of summer drought that induces nitrate accumulation. Corn that is ensiled 2 to 6 days after late frostdamage can also have high nitrate levels and shouldbe tested prior to use. Ship a small plastic bag ofsilage to the testing lab or bring it to your countyExtension office. Risk Management. An additional concern toranchers is the possibility of bloat that comes from the change of feed in turning livestock intodamaged corn fields. Fresh corn forage will behigher in nutrients and protein than the previousfeed. Cattle should be introduced slowly to the newfeed and watched carefully for signs of both bloatand nitrate poisoning. There is no substitute for a focused, calculatedtesting program to determine the concentration ofnitrates in damaged plant materials. But this iseasier said than done. Mixed plant materials arealways easier to evaluate than crop plants still in the field. Localized hot spots exist in the field for nitrates, justas with aflatoxin sampling. Once you have an idea asto how high nitrates are testing, you may be able toadjust a feeding program that will permit the salvageof some forage. Until adequate rainfall flushesnitrates from live corn plants, livestock owners andmanagers must closely monitor herd health and beready to withdraw the herd, feed, or provideintravenous injections as required. This report does not encourage or discourage theuse of drought-damaged corn for livestock feeding.It was prepared to provide an awareness of theoptions, risk, and precautions associated with thebuying, selling, or utilizing of these materials asfeeds or supplements. No nutritional or toxicologicalrecommendations have been intended, as thesecannot be determined without quantitative testing.The local large animal veterinarian, the forage labwith nitrate testing facilities, and the TexasAgricultural Extension Service are each capable of answering specific questions beyond the scope of this publication. For More Information. “Nitrate Poisoning in Beef Cattle.” TexasAgricultural Extension Service publication BCM-42,4pp. 1995 Beef Cattle Management Handbook, TexasA&M University System, College Station, Texas. The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that nodiscrimination is intended and no endorsement by the Texas Agricultural Extension Service is implied.Elizabeth Gregory, EditorRhonda R. Kappler, Graphic Designer

Preventing Nitrate Problems in Drought Damaged Corn

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Preventing Nitrate Problems in Drought Damaged Corn

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