Currently, there is no cost-effective and practical method to detoxify mycotoxin-contaminated grain or feed on a large scale. That is why today, one of the most practical approaches to controlling against toxins consists of adding adsorbent materials to animal diets to reduce absorption in the gastrointestinal tract. Clays are an important group of products that have been successfully used worldwide to reduce mycotoxicosis.
Though they are often grouped into a single category, clays are complex and widely diverse aluminosilicates with a variety of functional properties.
This is very misleading since there are many types of clays, which are completely different from one another. Because of this variety, there are many clays that do not capture mycotoxins; some can absorb water, others ammonia, and only a few can adsorb mycotoxins. The first effective mineral adsorbent described for a mycotoxin was the broad category of hydrated sodium calcium aluminum silicate (HSCAS). Since HSCAS is a generic description, it does not specifically define the material of use.
The majority of mycotoxin binding products are classified as montmorillonite, belonging to the phyllosilicate group composed of layers of aluminum and silicon connected in a 1:1 or 2:1 arrangement. Not all clays that adsorb mycotoxins are equally effective in protecting animals against the toxic effects of mycotoxins. Even some montmorillonite adsorbents are not always the best binders. Furthermore, the adsorption ability of similar clays may vary from one geological deposit to another.
Besides their origin, formation, and structure, clays can vary in chemical composition, surface acidity (pH), electrical charges (polarity), distribution of exchangeable cations, porosity, and expansibility characteristics. Despite all these differences, there is no significant correlation between any single physical or chemical property and the mycotoxin binding capacity of clays. Therefore, the effectiveness of a mycotoxin adsorbent is tested by conducting evaluations in vitro and in vivo to demonstrate a statistically significant response in preventing mycotoxicosis. The dosage of the adsorbent and the level of the mycotoxin used in these tests must always be reported. Also, it is important to demonstrate the innocence of the product when it is evaluated without the presence of mycotoxins.
The in vitro test must be conducted with high-performance liquid chromatography (HPLC) using a methodology using two types of solutions: one of pH 3 and another of pH 6, mimicking the gastric and intestinal juices. For the in vivo test, there is a standard experimental protocol consisting of four treatments: a control without mycotoxins; a control with adsorbent; a control with mycotoxin; and one with mycotoxin plus adsorbent. Additional treatments can be added to this experimental design, such as different testing levels of the adsorbent.
The amount of an adsorbed mycotoxin is difficult to calculate; therefore in the in vivo trial, the efficacy of adsorption has to be determined by the animal’s performance (body weight gain, feed consumption, and feed efficiency) and the target organ protection. It is important to evaluate the target organ(s) since they reflect the specific damage of the mycotoxin. It is also necessary because some adsorbents base their effectiveness on a positive effect on performance, which is a result of the presence of enzymes, beneficial bacteria, yeast and/or immunostimulant in the composition of those products, and not mycotoxin adsorption.
During the last 20 years, various scientific studies have demonstrated that some aluminosilicates are very effective in preventing aflatoxicosis. In the program conducted by LAMIC in Brazil for approval of anti-mycotoxin additives, 16 out of the 32 products evaluated were proven to be effective against aflatoxin in broiler chickens. All the effective products are, or contain, clays. The majority of the clays that significantly reduce the toxic effects of aflatoxins report being effective at an inclusion rate of 5 or 10 kg per metric ton of feed. Only a few significantly prevented aflatoxicosis at 2.5 kg/mT of feed.
In conclusion, there are several types of clays, each with its own unique properties that make it either effective or ineffective against toxins. When selecting a clay-based additive for animal feed production, both in vivo and in vitro tests should be performed; they should also contain at least 4 test groups. Of the clays found to have an impact on toxins, very few products are effective against more than one type of mycotoxin.
Recently, specially purified phyllosilicates have been developed, which are capable of binding Fusarium toxins like zearalenone, deoxynivalenol, fumonisins, and T-2/HT-2 toxins. Another thing to consider when evaluating a toxin solution is the inclusion rate. Many are effective at a rate of 5 or 10 kg/mT but it is possible to both save space in the diet and protect against toxins with a solution that only requires an inclusion of 0.5 to 2.0 kg/mT.
Toxins are a growing concern for all animal production operations. With no way to prevent their presence on farms, protecting the animals with a binder is currently one of the most population solutions.
