Evidence of molds is typical under normal growing conditions, however, hail damaged, drought and/or damp growing conditions contribute to excess molds on maturing corn plants, according to Dr. Terry Mader, University of Nebraska Extension Beef Specialist. Toxins produced by mold are called mycotoxins. Aflatoxins and fusarium toxins, such as zearalenone and vomitoxin are mycotoxins of most concern to livestock producers. In general, aflatoxins are more prevalent under warm, dry conditions while Fusarium toxins are more prevalent under cool, damp conditions.
Generally, ruminants have a greater tolerance for mycotoxins and can handle longer periods of low-level intake as compared to simple stomach animals. It is postulated that the rumen microorganisms interact with to partially degrade the toxins before they are absorbed. Sheep appear to excrete significant amounts of aflatoxin in their urine with a minimum of damage to liver and, therefore, appear to be less susceptible to aflatoxin poisoning. Also, older animals are less susceptible to mycotoxin toxicity than are younger animals. Most mycotoxins, and aflatoxin in particular, are difficult to remove from feedstuffs. Ultraviolet irradiation and anhydrous ammonia under pressure will reduce the toxicity of aflatoxins and, if continued long enough, will deactivate them entirely.
Dry heat can be used to reduce aflatoxin levels in contaminated corn. Reductions from 60 to 90 percent in aflatoxin levels were observed when corn kernels were heated to over 300 degrees F for approximately 12 minutes. High temperatures may reduce feed value of corn, however. Also, cleaning or screening grain can remove as much as 50% of the toxins present. The degree to which fermentation, through ensiling of the corn plant, will destroy mycotoxins is not clearly known. If ensiled, proper ensiling is important to prevent further mold growth. Application of an inoculant to the green chop should enhance fermentation and aid the ensiling process.
Because of the identification of aflatoxin infested corn throughout the Midwest in recent years, the FDA has issued guidelines that allow for the interstate transportation of aflatoxin contaminated corn at levels above the typical 20 ppb. These guidelines are:
* Less than 20 ppb aflatoxins are allowed if the grain is destined for food use by humans, for feed use by
immature animals or use by lactating dairy cows, or its destination is not known;
* Less than 100 ppb aflatoxins if destined for breeding cattle, breeding swine or mature poultry;
* Less than 200 ppb aflatoxins if destined for finishing swine 100 lb. or heavier; or
* Less than 300 ppb aflatoxins if destined for finishing (feedlot) cattle.
State diagnostic laboratories and commercial laboratories with feed testing facilities will usually test for mycotoxins.
By Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln
Institute of Agriculture & Natural Resources