Adsorbent Compounds as Feed Additives to Reduce Mycotoxin Bioavailability
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Mycotoxin contamination of animal feed represents a worldwide problem for farmers and can cause serious diseases in animals as well as affecting productivity. A mycotoxin-contaminated diet may lead in farm animals to substantial economic losses due to feed refusal, poor feed conversion, diminished body weight gain, immunosuppression, interference with reproductive capacities and residues in animal products. In order to avoid animal mycotoxicosis, several strategies have been investigated that can be divided into biological, chemical and physical methods. The utilization of mycotoxin-binding adsorbents is the most applied physical method of protecting animals against the harmful effects of mycotoxin contaminated feed. Addition in the diet of nutritionally inert adsorbents (hydrated sodium calcium aluminosilicates, activated carbon, bentonite, clays and special polymers) reduces the absorption of mycotoxins from the gastrointestinal tract thus avoiding or reducing the toxic effects for livestock and the carryover of mycotoxins into animal products. The efficiency of the adsorption depends on the chemical structure of both the adsorbent and the mycotoxin. Before applying this technique for routine use it is essential to establish that the absorbent does not remove essential nutrients from the diet.This fact sheet briefly describes the most important types of adsorbents and their effectiveness when added to animal feed. Hydrated Sodium Calcium Aluminosilicates Phillips et al. (1988) showed that hydrated sodium calcium aluminosilicates (HSCAS) have high affinity for aflatoxin B1 after screening 38 different adsorbents that were representative of the major chemical class of aluminas, silicas and aluminosilicates (1). The good stability of the aflatoxin-HSCAS complexes at pH 2-10 and up to 37 Deg C could explain the in vivo effectiveness of these adsorbents (2). HSCAS are phyllosilicate clays which are very effective with regard to preventing aflatoxicosis in a variety of animals, including chickens, turkey poultry, goats, cows, pigs, lambs and mink (3). HSCAS decreased the level of aflatoxin M1 residues in milk from lactating dairy cattle and in dairy goat milk fed with diet contaminated with aflatoxin B1 (4, 5). However the efficacy of HSCAS was quite limited against zearalenone (ZEA) and ochratoxin A (OTA) and totally ineffective for trichothecenes such as T-2 toxin, diacetoxyscirpenol (DAS) and deoxynivalenol (DON). Activated Carbon Activated carbon (AC), a insoluble powder formed by pyrolysis of different kinds of organic materials, shows different adsorbing properties depending on its origin. Surface area of activated carbons may vary from 500 to 2000 m2/g and up to 3500 m2/g for superactive carbons. Beneficial effects of AC have been shown in rats intoxicated with T-2 toxin. The mechanism of this beneficial effect has been associated with the ability, shown in vitro, of the AC to bind the mycotoxin, preventing its absorption and especially enterohepatic recirculation (3). AC has been shown to be effective in reducing AFB1 carry-over from feed to milk as aflatoxin M1 in lactating cows (6). AC showed in vitro the capacity to adsorb fumonisin B1 (FB1) from aqueous solutions but it was ineffective in reducing the toxic effects of fumonisins (increase of the sphinganine/sphingosine ratio in urine) in in vivo experiments performed on rats fed with fumonisin contaminated diets (7). AC is quite effective for adsorbing OTA from aqueous solution but has no beneficial effect when tested in vivo (8). Cholestyramine Cholestyramine (CH), a resin used for pharmaceutical purposes in decreasing total and LDL cholesterol, adsorbed almost 100% of ZEA from gastric and intestinal simulated fluids when used at a concentration over 1%. 1 gram of CH was able to adsorb up to 2 mg of ZEA (3). Experiments performed by incubating FB1 (up to 0.2 mg/ml) with 1mg/ml CH showed high affinity for FB1, adsorbing up to 85% of the mycotoxin from aqueous solution. The effectiveness of the CH against fumonisins was confirmed by in vivo experiments with rats, using the increase of the biomarker sphinganine/sphingosine ratio in urine and kidney to display quantitatively the bioavailability of fumonisins (10). In studies on rats CH was tested as a protective agent against OTA-induced nephrotoxicity and was found able to decrease the concentration of OTA in plasma, the excretion of OTA and its metabolites in urine and bile and to increase OTA excretion in feces (10, 11). However, some authors consider that the high cost of CH would make its commercial use economically prohibitive (12). Bentonite Sodium bentonite has been used as a binding and lubricating agent in the production of pelletted feeds. The addition of bentonite to a T-2-contaminated diet could have beneficial effects on the rats by reducing the transit time of digestion through the gastrointestinal tract and promoting fecal losses of the toxin. However bentonite was ineffective against ZEA and nivalenol (NIV) in pigs. The findings of several in vivo experiments to test the efficacy of this adsorbent for aflatoxins are contrasting and do not give consistent results (3). Other Adsorbent Compounds Divinylbenzene-styrene polymers (anion-exchange resins) exhibited beneficial effects when added to diet of T-2 intoxicated rats, minimizing the reduction in feed consumption and the growth-depressing effect caused by T-2 toxin. The addition of the divinylbenzene-styrene to diets of rats supplemented with ZEA resulted in a major decrease in urinary excretion of conjugated ZEA and its metabolites (3). Polyvinylpyrrolidone (0.2%) added to the diets of pigs contaminated with DON did not appear to alleviate the toxic effect of this toxin when fed to barrows and gilts over a period of 5 weeks (3). Commercial Products Recently a number of products have arrived on the food market claiming multi-mycotoxin binding capabilities. It is unfortunate that the results from only a limited number of sorbents have been peer-reviewed. To date some have these have been shown to effectively bind AFB1, while it has been difficult to objectively assess the ability of these sorbents to bind other mycotoxins. None of the sorbents has been scientifically proven to bind more than one mycotoxin simultaneously in in vivo studies. Conclusions The addition of different adsorbents to animal feed is the most applied way of protecting animals against mycotoxicosis, however so far, no single tested adsorbent has been shown to be effective against most types of mycotoxins. In addition, adsorbents showing in vitro high affinity for mycotoxins, have often not confirmed these results when tested in in vivo experiments. Widespread adoption of this approach depends on its effectiveness and its economics. References
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