Understanding And Preventing Feedborne Ins

Understanding and Preventing Feed borne Mycotoxins in livestock and poultry Dr.Kedar Karki Mycotoxin contamination of feed is, in many ways an unavoidable reality. It is believed that over 25 percent of the world’s grain supply is contaminated with mycotoxins. Mycotoxins can be carcinogenic and hepatoxic to both animals and humans. Mycotoxins are structurally diverse secondary metabolites of fungi that grow on a variety of feeds and foods consumed by animals and man, respectively. These chemically stable compounds are toxic to livestock when consumed in biologically significant amounts. The resulting diseases are referred to as mycotoxicosis. Mold growth and mycotoxin production on feed grains are influenced by many factors, but the most important of these is moisture. Stored grains should contain less than 15 percent moisture to minimize mold growth. Several trends have tended to increase the severity and economic importance of mycotoxins in animal and poultry agriculture in recent years. These trends are as follows: • Recent global weather patterns have been irregular with heavy rainfall and flooding in some areas coupled with drought and unusual frosts in other regions. • Drought stress can also lead to increased fungal penetrations of grains. The result has been an increased frequency of reports of mycotoxin contamination of feed grains. Some tropical and semitropical countries are reporting Fusarium contamination of crops where only aflatoxin was previously detected. • Another trend contributing to the frequency of mycotoxin contamination of feeds is improved global trading transportation systems and global trading of agricultural commodities. This allows more extensive shipping of grains and other feed components throughout the world. The result is that complete feeds are likely a more complex blend of feedstuffs with more widely varying geographic origins than was seen in the past. The potential for Aflatoxins and mixtures of Fusarium mycotoxins to be contaminants in feeds is, therefore, enhanced. The most commonly recognized feed borne mycotoxins are the Aflatoxins and the Fusarium mycotoxins. Fusarium fungi are commonly found in temperate climates; and Fusarium mycotoxins are likely the most economically significant grain

mycotoxins on a global basis. The numerous Fusarium mycotoxins are very diverse in chemical structure and in the characteristics of the mycotoxicosis they produce. These toxins include the trichothecenes, the fumonisins, zearalenone, moniliformin, and Fusaric acid. Major effects of Fusarium toxins on livestock and poultry? 1. Fumonisins a. Immunosuppression b. Leukoencephalomalecia in horse c. Lung edema in swine 2. T2 Toxin a. Inflammation of the GI tract b. Females don’t return to estrus c. Immunosupression d. Vomiting e. Beak and palate lesions f. Anorexia g. Blood pressure reduction h. Increased brain tryptophan levels (serotonin precursor) i. Reduced appetite 3. Zearalenone (Zen, Zea, F-2 Toxin): Found worldwide, particularly in corn(maize). a. Uterine prolapse b. Hyperestrogenism, abortions and embryo reabsorption c. Return to estrus d. Anestrus e. Ovarian and testicular atrophy f. Reduction in litter size g. Estrogenic properties 4. Vomitoxin/Deoxynivalenol (DON): Swine are the species most sensitive to dietary deoxynivalenol. Poultry are less sensitive and ruminants are the most resistant due to the action of the rumen microflora. a. Poor performance b. Anorexia c. Vomiting d. Increased brain tryptophan levels 5. Fusaric Acid a. Lethargy b. Anorexia

c. Vomiting d. Low blood pressure e. Inhibitors of cell protein synthesis, f. Increased brain tryptophan levels (serotonin precursor) g. Reduced appetite The non-specific nature of the symptoms of tricothecene toxicosis, including reduced feed consumptions, reduced growth and immunosuppression, make it difficult to confirm trichothecenes as the cause of lost performance. The cause could also be improper management practices or a wide range of health factors. It is now clear that toxicological synergism between different Fusarium mycotoxins can increase the toxicity of a given diet and incomplete analysis can, therefore, give false security as to the potential hazard posed by the feeding of contaminated grains. It is also important to remember that many different components of a complete feed can be vectors for mycotoxin contamination. Our studies indicated that the Fusaric acid content of complete feeds can exceed that found in individual feedstuffs. This has since been attributed to Fusaric acid contamination of soybean meal. Fusaric acid has been found in soybean plants and is considered a phytotoxin in various vegetables species. Mycotoxin binders are promising a ray of hope to minimize the problem.Mycotoxin binders are large molecular weight polymers that, when added to feed, are capable of forming irreversible complexes with mycotoxin molecules in the intestinal lumen. Such complexes are not digestible, pass down the digestive tract and are excreted in feces. The net effect is the reduced dosage of absorbed toxin to the point that it is below the biological threshold. This allows contaminated feed to be given with minimal losses in performance. The challenge is to identify compounds that can effectively bind a mixture of mycotoxins with widely varying molecular structures and polarities. The binder must also be effective at low levels of inclusion since these nonnutritive additives are diluents that will reduce the nutrient density of the diet. Activated charcoal is an example of a toxin binder that has been widely used in veterinary medicine to treat accidental acute poisonings. Mycotoxin binders can be silica based inorganic polymers or carbon-based organic polymers. The inorganic polymers currently on the market include natural clay products (HSCAS, bentonites, zeolites) as well as synthetic polymers. The advantage of the claybased products is their low price. Unfortunately these products also offer low specificity and must be used at a relatively high level of inclusion (5 kg/ton of feed) to be effective. This is the case for both

bentonine and spent canola oil bleaching clays when overcoming T-2 toxicosis. Synthetic inorganic polymers have usually been designed to effectively bind one specific mycotoxin, the aflatoxin. Such specific products are, therefore, much less effective against a mixture of mycotoxins of varying molecular weight and polarity. Synthetic products are inevitably more expensive than naturally-produced materials. Organic toxin binders are derived from plant or microbial fibers. Studies in our laboratory indicated that lignin-rich alfalfa fiber was quite effective at overcoming the toxicity of T-2 toxin and zearalenone. An advantage of using organic fibers as mycotoxin binders such as dehydrated alfalfa meal is that they have some dietary energy and protein content and do not act as dietary diluents in the manner of inorganic polymers. Alfalfa fiber, however, like clay-based products, is effective at only high levels of dietary inclusion. This makes such materials impractical when added to livestock and poultry diets. An innovation in mycotoxin binders is the concept of organic polymers derived from yeast cell wall. This material has a high surface area and enough specificity to allow effective mycotoxin binding at a low level of dietary inclusion.