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Mycotoxins are secondary metabolites of fungi that are toxic to other life forms. More than 250 mycotoxins have been detected, but relatively few are considered to be important to animal health.
Mycotoxin prevalence and concentration are sporadic and vary annually, even in the same location. Production is affected by local weather patterns, crop damage and productions practices. They may be produced pre- or post-harvest.
Mycotoxins known to occur in Iowa are aflatoxins, dicoumerol, ergot and endophyte-infected tall fescue, vomitoxin, and zearalenone. They are mostly found in grain, including corn, wheat, milo, rye, and oats. They may be found in silages or other feeds which contain grain. With the exception of sweet clover and fescue, they are rarely found in forages.
Since there are many kinds of mycotoxins, which differ from each other, they produce many different kinds of diseases, called mycotoxicoses. They may cause diseases of the liver, alimentary canal, smooth muscles, or kidneys. Mycotoxicoses are not contagious.
Effects of the mycotoxins known to occur in Iowa are described in Table 1 below.
Detection of mycotoxins:
Detection of mycotoxins in feeds can aid in the prevention and diagnoses of mycotoxicoses.
Chemical analysis is the best way to find mycotoxins in feed. Screening methods are commonly used to rapidly detect mycotoxins. Positive results obtained by most screening methods do not prove the presence of mycotoxins, so positive results should be checked using methods that can prove their presence.
Screening for mycotoxins in feeds by black light (ultra-violet light) is not reliable. Detection is based upon the fluorescence of chemicals indicative of the presence of mycotoxins, which occurs when the black light shines on them. Most mycotoxins do not fluoresce. Those that do may cause adverse health effects at concentrations too low to be detected by the black light. Chemicals that are not mycotoxins may also fluoresce, causing false positive results.
Sampling for analysis:
Mycotoxins are not evenly distributed in feeds. Some areas may contain very high concentrations, other areas may contain no detectable amounts. So detection in feeds depends upon the quality and quantity of sample provided for analysis. The sample should reflect all of the feed available at the time the problem occurred. The longer sample is collected after onset of animal health problems, the more likely the feed from which the sample is collected will not be characteristic of the feed being eaten at the time the problem began. And, the smaller the sample collected and provided for analysis, the more likely mycotoxin contamination will be missed.
Sampling based upon visible presence of molds does not always provide a sample that contains mycotoxins. The presence or absence of visible mold growth are not reliable indicators of the presence or absence of mycotoxins. Very moldy feed may not contain any detectable amounts of know mycotoxins, while good looking feed may contain very high concentrations.
It is best to collect a sample during movement of the feed, like when augering it from the storage bin into a grain truck. Collect small amounts over the entire time the feed is being moved, so that at least 5 pounds, and as much as 10 pounds, have been collected. Otherwise, probe sampling may be used. Collect probe samples from as many areas of the feed as practical.
Dry samples are preferred for transport to the laboratory. Mold may grow on wet sample, especially if the sample is placed in a plastic bag. Oven-dry specimens to less than 13% moisture for best preservation. Ship samples in paper or cloth bags.
See the ISU VDL User Guide for specific submission guidelines.
Use of mycotoxin-contaminated feeds:
It is always safest not to use moldy or mycotoxin-contaminated feeds. Even if no detectable amounts of known mycotoxins are found in moldy feed, as yet unknown mycotoxins may be present which cannot be detected. It is best to NEVER use corn screenings for horses. Corn screenings are very likely to contain toxic concentrations of fumonisins.
If mycotoxin-contaminated feed must be used, feed it to animals that are least sensitive to its adverse health effects, or blend it with clean feed to reduce the concentration to acceptable levels. Generally, ruminants are least affected by mycotoxins. Avoid use for any breeding or gestating animals. Requirements or recommendations for mycotoxin content of feeds may be found in Table 2.
If mycotoxin-contaminated feed is to be blended, then the mycotoxin content of the “clean” and mycotoxin-contaminated feeds must be known. The following formula may be used to calculate the amount of clean feed necessary to make feed containing acceptable mycotoxin concentrations.
x = (C-L)/(H-L)
x = fraction of the mycotoxin-contaminated feed in the blended feed
Chemicals which are supposed to bind mycotoxins, are available. The binder is mixed in with the mycotoxin-contaminated feed to bind mycotoxins, reducing or preventing absorption into the body. The theory upon which binding is based is sound, however efficacy for all mycotoxins in any feed for all animals is uncertain. The binders may also prevent the absorption of nutrients in the feed, too. We urge caution regarding their use.