No Easy Answers to the Mycotoxin Dilemma

Despite extensive research and on-farm experience around the world, there is still much to learn about mold and mycotoxins. There are currently about 300 documented mycotoxins, with new ones still being identified. Lagging behind the process of identifying these toxins is the discovery of details behind their clinical effects on humans and animals.

Although researchers have attempted to link field incidences of mold to particular toxins, the process of correlating this information is far from straightforward. Take into consideration that:

     * Mycotoxins often occur in very low concentrations that may be difficult to detect
     * Analysis may not give a true assessment of the situation because the methodology is not sufficiently
       developed, or unidentified mycotoxins may be present
     * Clinical symptoms are often not obvious or unique - typical observations, such as lethargy, decreased
       feed intake, poor performance or increased susceptibility to infection, could be caused by a number of
       other health or management factors
     * There is no typical dose-response with mycotoxins as seen with other disease organisms
     * Interactions between individual mycotoxins are not well characterized. Since contaminated feed usually
       contains a number of different mycotoxins, some of which might not yet be identified or well known, the
       interpretation of what is happening becomes increasingly difficult

Although many different mycotoxins have been identified, the majority are detected in samples at very minute quantities. The most common mycotoxin, although it is not the most toxic, is deoxynivalenol (DON or vomitoxin). However, the toxicology, biology and chemistry of the various mycotoxins are diverse. As a result, the effects vary widely and depend on many factors, such as toxin intake, duration of exposure, species, age, gender, physiological status, and the synergies between different mycotoxins present in the feed.

They say that the best defense is a good offense. So, an important first step in controlling mycotoxins is first controlling mold growth. This can be done by:

     * Maintaining low feed moisture - ideally moisture levels should be around 12-15%
     * Keeping feed fresh - it takes time and the appropriate environment for mold to grow
     * Keeping mixing equipment and feeders clean - contaminated surfaces or feed can inoculate clean feed
     * Keeping the grain intact until it is dried - mold growth is more likely to occur in damaged or processed
       grains
     * Using mold inhibitors - these products will have no effect on mycotoxins but they will inhibit further mold
       growth

Other than the typical approach of diluting mycotoxin-contaminated grains in rations, in the past research has concentrated on the identification of binding agents to alleviate the effect of mycotoxins. The ideal mycotoxin binder has the following characteristics:

     * Highly specific to bind a specific mycotoxin or mycotoxins - if the binding agent is not specific, it may bind
       to other nutrients or medications in the diet, reducing their availability and effectiveness
     * Low level of inclusion - binding agents usually do not add nutritional value to the feed, so inclusion levels
        need to be kept low to minimize dilution of dietary nutrients
     * Technically and economically feasible

Researchers have studied many different additives, including bentonites, zeolites, bleaching clays, activated carbons, alfalfa, and others. Although these additives have proven to be effective at binding mycotoxins, they have also been known to indiscriminately bind other dietary components, such as vitamins, minerals and drugs. In addition, many require high inclusion levels, effectively adding a dilution factor to the diet. As a result, binding agents are often deemed impractical.

Recent research efforts are concentrating on more sophisticated additives and nutritional approaches. Researchers are currently looking into the potential of organic polymers like esterified glucomannans, an extract from the cell wall of yeast. This extract has demonstrated a strong affinity for some mycotoxins, like aflatoxin, yet it does not interfere with mineral metabolism, as has been observed with some binding agents, like activated charcoal. Preliminary results from laboratory and animals trials have been promising.

Since the process of developing binding agents specific to particular mycotoxins is complex, other researchers are exploring unique nutritional strategies. Research at the University of Guelph has been concentrating on dietary manipulation to overcome mycotoxicoses. Dr. Trevor Smith is researching the potential for specific feed ingredients to manipulate brain neurochemistry. One approach is to feed protein supplements, such as corn gluten meal and blood protein supplements, that are rich in large neutral amino acids. These large neutral amino acids compete with tryptophan for transport sites through the blood-brain barrier, effectively reducing the amount of tryptophan that enters the brain and, as a result, reducing the amount of serotonin produced. Serotonin is a brain neurotransmitter that, when produced at increased levels, results in lethargy and loss of appetite. Research to date has proven this technique to be successful for starter pigs consuming DON-contaminated feeds.

It is obvious that continued, extensive research is needed in the whole area of mold and mycotoxins. In this case, what we don't know can hurt us. Be sure to sample and test suspect grains for mycotoxins prior to feeding, to determine exactly how much of the ingredient can be safely included in rations.

References:

Prelusky, D.B., Rotter, B.A., and Rotter, R.G. 1994. Toxicology of Mycotoxins. IN: Mycotoxins in Grain: Compounds Other than Aflatoxin. Ed. Miller, D., and Trenholm, H.L. p. 359.

Piva, A. and Galvano, F. 1999. Nutritional approaches to reduce the impact of mycotoxins. IN: Biotechnology in the Feed Industry 1999. Ed. Lyons, T.P. and Jacques, K.A. p. 381.

Newman, K. 2000. The biochemistry behind esterified glucomannans - titrating mycotoxins out of the diet. IN: Biotechnology in the Feed Industry 2000. Ed. Lyons, T.P. and Jacques, K.A. p. 369.

Smith, T.K., Modirsanei, M., and MacDonald, E.J. 2000. The use of binding agents and amino acid supplements for dietary treatment of Fusarium mycotoxicoses. IN: Biotechnology in the Feed Industry 2000. Ed. Lyons, T.P. and Jacques, K.A. p. 383.

By Janice Murphy - Swine Nutritionist/OMAFRA
Government of Ontario, Ministry of Agriculture, Food and Rural Affairs website