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August 2013 – Drought and Livestock

     July, 2012


     This year we have a great potential for nitrate-nitrite and possibly cyanide poisoning in our livestock.  Many of the irrigation ditches ran out of water before July, which is very rare.  When a crop is stressed there are many potential problems that can develop.  If you are buying any 3rd cutting hay or any CRP/prairie hay we recommend that you ask your hay seller if they have tested a portion of that cutting for nitrate problems.  Our local Weld County Laboratories in Greeley (, 970-353-8118) can provide a nutritional hay analysis with a nitrate test for less than $30.  We recommend at a minimum this nitrate by the chemical method plus the basic NIR package (moisture, protein, ADF, NDF, calcium phosphorous, potassium and magnesium) for all late forages this year.  For silage that is stressed we recommend the Weld Laboratory’s silage test plus the prussic acid & nitrate. It should be noted that for cattle on feed the relative feed value (RFV) tests are also to be considered for any hay, silage or forage test.  Our local CSU extension office at the Boulder County Fairgrounds (303-678-6238) has hay probes available for rent. Weld Laboratories also has rental hay probes.  If you are feeding oat hay to your cattle this should also be tested if the crop was short on water.  If you have never collected forage sample we recommend visiting If you rent a hay/forage core probe there are also videos and direction for each type of probe on the internet.  The recommendation is to test 20% of the bales or up to 20 samples mixed into one sample bag. 

     If the hay field is near the foothills a selenium test for $25 is available at the Weld Labs if you are concerned and/or want to balance the selenium requirements.  A selenium test over 5 ppm is a concern. 

     When hay prices are short the baling of stover (corn stalks) and straw products understandably increases for use in livestock feeding; we recommend that this year you test these corn stalks before you purchase such bales.  The prussic acid test for cyanide is less than $30 at Weld Laboratories using the more accurate method of testing.  A prussic acid test < 600 ppm is okay, while >1,000 ppm requires one to dilute out this feed.  Properly grown, harvested and cured silage should usually have a low prussic acid test, and this is not a routinely a test that is needed every year. 

     If you look at the hay or field at dawn, and the plants are wilted this early in the morning, you should consider testing the crop.  If you plan to graze stover and you know the field was stressed, we recommend the cyanide and nitrate-nitrite tests and for the $15 more also the basic NIR package.  To collect fresh samples in the field cut 10x corn stalks at 6″ above the ground in 2-4′ lengths, then at home cut up these stalks further into 6″ or less pieces and mix them up and place in a zip lock bag for shipping to the laboratory These samples need to be kept chilled, yet not frozen until shipped with an ice pack, as the prussic acid (hydrocyanic acid/HCN) level will be lowered if not refrigerated. The prussic acid test will also be altered if the sample is frozen.  To collect forage samples in the field for nitrate testing cut the plants about 4-6″ up off the ground (or near ground level if the plant is shorter in size).  Keep these samples refrigerated until delivery for testing. An ice pack is recommended.  Our clinic usually has available some ice packs and Styrofoam shipping boxes free for currently active clients.  To test for both cyanide (prussic acid) and nitrate-nitrite these samples can be sent to Weld County Laboratories.  We recommend that you drop off the samples in Greeley instead of shipping by mail, if possible.  You can also send your forage samples to Servi-Tech at  As FYI if you are looking only for prussic acid/cyanide problems then pick the leaves in the upper half of the stalk still standing in the field and make an “X” walk across the field by walking diagonally across the field to collect the samples.  If also collecting for nitrate toxicity you will also want to include the lower stalks or the whole plant is ok being chopped up for both tests.  The best time to collect such fresh field samples is in the middle of the day. 

     If you have stressed field picking corn you may want to collect 10 ears of corn for aflatoxin testing at one of the mycotoxin testing laboratories:,, We have a list of other testing laboratories available.  Before taking or sending off samples always check the lab for their preferred method of collection and shipping.  

     If in a drought you had to switch your irrigating practices to shut off/switch the water when it had gone 3/4 of the way through the field, then the lower part of this field should be tested for nitrate-nitrate in hay and in corn for cyanide plus nitrate-nitrite.  If these tests are high in nitrate then there are ways to work with the feed and by testing other forages and you can dilute this potential problem forage for use in cattle. We have more information if needed.  A nitrate level less than 5,000 ppm is at a high “okay” level but >10,000 ppm it is dangerously toxic.  For pregnant livestock a level over 1500 ppm nitrogen-nitrate is a concern. This figure multiplied by 4.42 is 6,600 ppm nitrate.  If you find moderate levels of nitrate in your forage then for your pregnant animals other forage and water sources should maybe be tested if you have never done this. Also limit the NPN tubs to reduce a cumulative effect which can cause abortions and death.  A water sample of 30 ppm nitrate should be a concern.  The overall nitrate level for a steer should be 14 mg/# of NO3-N per day or less, but only 5 mg/# of Nitrate-nitrogen for a pregnant animal!  It is confusing that the testing results the lab may use.  If the lab reports the level in nitrate-nitrogen multiple the figure by 4.42 for the nitrate level; if the report is in % nitrate, you can then multiple this percentage by 10,000 for ppm.  If the level is provided in potassium nitrate, then multiply the number by 1.75 to obtain the nitrate-nitrogen figure (or 7.72/4.42).  Luckily most labs report the type of nitrate test and if this test is at a toxic level.

     If you are turning your livestock out onto a pasture of weeds that have been stressed, a potential nitrate problem can occur. Some weeds can be more toxic than drought stressed hay or corn.  It is the broad leaf weeds which are of the most concern. Our poisonous plant handout for livestock lists many of these weeds.  Consider testing the stressed forage in this pasture, or at minimum then feed 70+% of the livestock’s needs per day with quality hay daily (>1% of body weight) and use a strip grazing method.  If grazing stressed stover consider pre knocking down/mowing some of the rows to enable you to move the electric fence for the addition of only a few rows every few days, plus supplemental feeding of the cows for over half of their nutritional needs; one can encircle the whole field with the electric fence and use two rows of a quick-release/gate type connections to disconnect one cross fence line and active the next row.  This fall one can also consider testing the soil for fertilizing for a maximum production next year; at http://anr.ext/>soil there is a video on how to collect a soil sample.  Our local CSU extension office also has soil probes, directions and the samples can be tested at CSU ( or at Weld Laboratories in Greeley.        If the purchased hay is tested and there are potential problems, the hay seller should be notified and the problem documented.  When buying hay in volume anytime, especially this year, first ask the seller if they have a forage test available for the cutting you are purchasing.  Since we have had record prices for hay the last two years, and a major drought, there will be some hay baled this year that should not have been.  If you find a lot of broad leaf weeds in the hay, then the nitrate test is recommended (and for $15 more the forage analysis panel by the NIR testing method).  Anytime over $500 of hay is purchased at a hay auction it may be cost effective to do a routine hay forage analysis with a nitrate test.

     For livestock the use of protein tubs should be cost effective this winter; we have a comparison analysis sheet available.  Horses and non-ruminants should not be fed non-protein nitrogen (NPN) supplements.  If feeding a NPN protein tub we recommend that the hay should especially be tested for nitrates if it was a late cutting and/or CRP hay, imported from another area, auction hay, or etc.  As mentioned, pregnant cows should not be on high nitrate level hay and/or a high nitrate water source plus NPN protein tubs.  

     In 2012 we will be providing the ability to have your forage and soil samples taken to Weld County Laboratories, if you cannot easily take them to Greeley.  We have arraigned a courier service to collect the samples on Monday and Wednesday of each week; you will need to have the samples at the clinic by 5 pm.  You will first need to contact the laboratory at 970-353-8118 and arrange to prepay for the tests to be delivered; you should and also rent a forage or soil sampler from the extension office before you collect and pre-pay for the tests.  The costs for this delivery service is $5 cash for currently active clients, or $8 for non-active clients without a product/service purchased within the last 3 years from the clinic.  Ensure that these samples are properly labeled by contacting the lab first.  Below is our drought handout which may explain other concerns.  






     Drought is a cycle that will occur every decade or so in our area.  We cannot always plan for or predict a drought.  Hopefully we can learn from mistakes we have made during the last drought cycle(s).

     Feed is a major cost for livestock when one has to supply the forage.  Pasture is the least cost method of maintaining and feeding animals if the vegetation is adequate and nutritious.  Our cow feeding handout has some information about by-products and alternative feeds, winter feeding on pasture, etc.  When hay prices are high some horse owners tend to purchase the Sudan hays, such as oat hay.  Sudan poisoning can occur in horses even though this same hay can be fed safely to cattle.  Ask for our horse Sudan poisoning handout if you area feeding oat type hay to horses.  We also do not recommend feeding oat hay to male goats, sheep or male camelids, due to urolithiasis problems.

     Protein may need to be supplemented.  We do not recommend over 1/3 of the diet as NPN to be fed to ruminants; these are usually tubs of molasses containing urea.  NPN should not be fed to horses and camelids.  If you have experienced a grass tetany (low magnesium), a milk fever (low calcium) or a low phosphorous problem in your herd please ask for our comparison information for these protein tubs.  Even though alfalfa hay or pellets may be more expensive, this legume hay usually is a good, safe source of natural protein for livestock and horses.  Never feed moldy hay to animals.  Feeding an ionophore (i.e. 200 mg monensin) in two pounds of a 30% crude protein supplement can be considered for cattle on a prairie hay pasture.  In a drought, hay testing becomes very important to help balance a ration; also reducing the herd to 75% of the carrying capacity of the land should also be considered.  If forage is limited, then 6 hours of access to hay can be a minimum amount to keep up the cows maintenance level and reduce overgrazing on your pasture.  Our winter feeding tips handout discusses the amount of hay lost when you feed on the ground versus in feeders or etc.  We have other low cost feeding mixtures if you have the ability for a TMR ration and over 50+ head of cattle to feed through the winter.  For most farms we instead recommend the NPN winter range tubs, if they calculate to be cost effective over your own grown or purchased hay crop.

     When there are periods of drought we see nutritional problems not normally seen when food is plentiful.  Cyanide poisoning can occur when cattle are allowed to graze corn that is drought stressed.  If you cannot harvest corn properly let it dry in the field, and be aware of the mature cow who knows how to eat the ears (only) off the corn stocks as she goes through the field; grain overload can then occur.  Rotational type fencing helps the cattle to graze only a small, new part of the field each day or so in the late fall or winter.  Ensilaging stressed corn can also cause a cyanide poisoning.  Nitrate poisoning can also occur in corn during the same type of stressful conditions, and grazing access being limited to the stress corn is crucial.  Nitrate poisoning also can be seen with broadleaf weeds undergoing stress, drought and/or weed spraying with 2-4 D.  If the hay has not been sprayed for insects blister beetle poisoning can occur, especially with stressed hay.  Many poisonous weeds, such as the white hoary alyssum, can thrive in a hay field undergoing stress and drought.

     When silage corn is harvested in a drought period it may not ferment properly if the silage was cut with a low moisture content.  Listeriosis, aflatoxin, vomit-toxin and other problems can be a result due to improper fermentation and/or feeding practices with silage from stressed plants.  Aflatoxin is produced by a mold growing on the corn, especially if stressed.  Ensilaging may kill the fungus but it will not kill the toxin.  Vomitoxin and other similar toxins can easily develop in feeds grown and processed in a drought.  If there is not enough grain to properly ferment the propionic, lactic and acetic acids then butyric acid can develop.  Using buffered propionic acid additives should be considered if diluting such marginal silage to feed out with other forages.  If one grazes the stressed corn the nitrate and cyanide poisoning problems can occur as mentioned above; and especially the cyanide problem if there has been a recent frost or first freeze.  Mowed Sudan (corn, oat hay, etc) which has been left alone for a few days will allow some of the cyanide to escape; yet as to be mentioned below this sitting can worsen a nitrate problem.  We recommend testing drought affected Sudan forages possibly before harvesting and/or definitely before feeding to livestock; we have a list of the laboratories which will do forage testingIf the forage has a high nitrate content in the field the silage chopper can be adjusted higher, as the lower part of the stock contains a lot of nitrate.  Ensilaging can remove up to 1/3 of these nitrates.  Nitrogen oxide is released and can cause silage poisoning in humans which can occur if one enters a silo within 3-4 weeks of filling; turning on the silo fan 15+ minutes before entering helps reduce this problem.  Allowing this green chop hay to sit and heat up may cause a higher nitrite level to develop from the nitrates in the hay.  Nitrite is 10x more toxic than nitrate.  Feeding green chop silage fresh can be the most hazardous method if allowed to sit, yet feeding as fresh chop within a few hours this may be adequate if the nitrate levels are not high and the feed is mixed with other forages or feeds.  The nitrogen oxide gasses from high nitrate silage can kill cattle (and humans) within 12-60 hours after harvesting.  (As noted above green chop silage after a frost can create a cyanide problem).  If the corn is left to dry in the field, and cattle are allowed to graze down the corn, to prevent acidosis and grain overload/bloat you should SLOWLY strip graze the corn as mentioned above for cyanide problems, and feed hay before turning out the cattle into the new small strip.  If you think you have a high nitrate forage, we recommend you test the field before harvesting.  When cutting stressed, high nitrate corn for silage, remember that the lower part of the stock can have the highest concentrate of toxic compounds; something to remember if you are thinking of turning cattle immediately out onto the corn stover after harvest.  This nitrate concentration especially occurs during a drought, and also if there is a wet period in the fall before the corn is harvested. 

     Minerals need to be supplemented in a drought.  We strongly recommend the brown mineral salt blocks for all livestock.  In a drought phosphorus is also one of the limiting factors, and simple mixing dicalcium phosphate with the trace mineral salt (50/50 mixture) should resolve this problem.

     Water should be located every 1/2 mile if possible.  When a cow has to walk more than 1 mile to water, a lot of energy is wasted.  Place the salt blocks 1/4 mile away from the water source and/or protein tubs.  Placing them together will cause the cattle to stay in one spot and create problems by destroying the vegetation.  Move these salt and protein supplemental tubs periodically.

     Vitamin A is a concern, especially if the forage or supplemental hay is not green in color.  It is especially important to give a vitamin A injection to newborn livestock born during a drought.


The Staff at the Nelson Road Veterinary Clinic