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Extension > Agriculture > Dairy Extension > Feed and Nutrition > Drought-stressed crops used for feed should first be tested for toxicity

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Drought-stressed crops used for feed should first be tested for toxicity

Dr. Mike Murphy

There were areas of Minnesota under severe drought this past growing season. Many farmers who live in these areas harvest the crops for livestock feed. There are potential problems for livestock producers that must be considered before any crop is fed.

  1. Corn: The three topics of greatest concern are nutritional value, nitrate concentration and mycotoxins.
    • Consider testing for the nutritional value of corn and corn silage grown under drought conditions as it may be lower than that grown under more normal conditions.
    • Plants that have taken up nitrogen for growth and have been stunted due to drought may have higher nitrate than normal. With normal nitrate concentrations, the animal's rumen microflora do a great job of reducing this nitrate to ammonia, then using this ammonia to make amino acids and proteins, just like non-protein nitrogen supplementation. When the TOTAL RATION nitrate level exceeds 5,000 ppm (0.5 %) there is a risk that the rumen microflora cannot reduce all nitrate to ammonia. Many cattle are at risk of nitrate toxicosis when it exceeds 10,000 ppm (1%) increasing the possibility of both abortion and death in previously unexposed cows. (Note: values are for nitrate. Multiply Nitrate Nitrogen results by 4.4 to calculate the nitrate concentration). Nitrate toxicosis is normally seen as a sudden death. Abortion of cattle in the second or third stage of gestation has also been observed. Testing silage three or more weeks after filling the silo to determine the actual nitrate concentration is recommended.
      Although alfalfa, clovers and grass hays are normally in the few hundred ppm range, they may be higher in drought years, especially with nitrogen fertilization. Corn grain, soybeans and cottonseed do not normally contain appreciable amounts of nitrate.
    • Mycotoxins: Corn is commonly exposed to a number of molds in the field. Fusarium sp molds are associated with stalk rot in wet years and with the pink mold on ears that have hail damage. Some strains of Fusarium mold may produce mold toxins, called mycotoxins. Strains of Aspergillus species may produce the mycotoxin called aflatoxin in hot humid weather. Aflatoxin is a carcinogen and its metabolite, aflatoxin M1, passes into the milk of cattle ingesting aflatoxin containing feed. U.S. Federal Food and Drug Administration regulations indicate grain may not contain more than 20 ppb (that's parts per billion) aflatoxin if intended for use in dairy cattle. Milk is checked for aflatoxin at a sensitivity of 0.5 ppb. Cattle ingesting as little as 20 to 50 ppb in the total ration may have more than 0.5 ppb aflatoxin M1 in their milk, and therefore, more than likely it will be dumped. Use of corn containing greater than 20 ppb aflatoxin is strongly discouraged for lactating dairy cattle rations. The use of binding agents in dairy rations does not guarantee that aflatoxin M1 will not occur in the milk of lactating cattle ingesting aflatoxin containing feed.

      Consider testing corn and corn silage for aflatoxin this year. Note: the presence of mold does not mean that mycotoxins have been produced, and mycotoxins can be produced without mold being visible.
      Corn smut replaces the normal corn kernels with large distorted growths called "galls" but these have not been associated with toxicity.
  2. Soybeans: Weed seed contamination, especially nightshade seed contamination can produce gastrointestinal upset and/or neurological signs in cattle.
  3. Cottonseed: Many of the cotton producing states also experienced a drought this year. Two toxins of concern in cottonseed are aflatoxin and gossypol. Gossypol is not normally a concern unless fed at a rate greater than 6 to 7 pounds per head per day in mature cattle. Consider testing your cottonseed for aflatoxin this year.
  4. Hay: Moldy sweetclover, if present on CRP land used for hay production this year may produce dicumerol. Dicumerol may induce abortions and bleeding in cattle ingesting toxic doses of it. Probe bales to determine dicumerol content. Rotation of cattle off sweetclover hay and onto fresh alfalfa hay is one way to manage the dicumerol problem.

Sampling After Harvest:

Generally samples for mold and yeast counts should be collected in to a paper bag, kept cool on ice, but not frozen, and delivered to the laboratory within 24 hours. Samples of dry grain or hay may be sent in a paper bag for nutritional analyses, mold and mycotoxins testing, dicumerol and nitrate testing.

Tests to Consider:

Please consult with your veterinarian, extension educator, nutritionist and other agriculture professionals to consider whether any of the above toxins may be present in your feed and for information on laboratories that will run a sample analysis.

Published in Dairy Star October 28, 2006

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