The effectiveness of an anti-mycotoxin additive cannot be based only on in vitro trials anymore; it has to be evaluated by conducting in vivo tests using a scientific experimental design measuring the beneficial effects of the product on target organ protection and animal performance.
By Douglas Zaviezo, Special Nutrients, Miami, Fl, USA
Practical methods to detoxify grain or feed contaminated with mycotoxins on a large scale and in a cost-effective manner are not currently available. At present, one of the most practical approaches consists of using adsorbent materials in animal diets to reduce the absorption of mycotoxins from the gastrointestinal tract. Clays are an important group of products that have been used successfully worldwide to reduce mycotoxicosis; and all commercial anti-mycotoxin additives available in the market are clay based products.
Clays are complex and widely diverse aluminosilicates with a variety of functional properties, but they are often grouped into a single category. This is very misleading since there are many types of clays, which are completely different from one another. Many types of clays do not capture mycotoxins; some can absorb water, others can absorb ammonia, and only certain clays can adsorb mycotoxins. Not all clays that adsorb mycotoxins are equally effective in protecting animals against their toxic effects. Furthermore, similar clays may vary from one geological deposit to another. It is critical that the origin (deposit) of the clay always be from the same source. Any scientific information obtained from a clay-based product is directly related to its origin and does not apply if there is a change in its geological deposit.
There is no significant correlation between any single physical or chemical property of clays and its mycotoxin binding capacity. Therefore, the effectiveness of any mycotoxin adsorbent (clay or its combination with yeast, enzyme or bacteria) has to be tested, performing in vitro and in vivo evaluations, to demonstrate a statistical significant response that it prevents 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 lack of nutrient adsorption and the innocuity of the product.
Anti-mycotoxin additives (AMA) evaluation
In vitro tests must be conducted with high performance liquid chromatography (HPLC) using a methodology involving two types of solutions: one with pH 3 and another with pH 6, mimicking the gastric and the intestinal juices.
In vivo testing has a standard experimental protocol consisting of four treatments: a control without mycotoxins; a control with adsorbent; a control with mycotoxin; and one group with mycotoxin plus adsorbent. Additional treatments can be added to this experimental design, such as different testing levels of the adsorbent.
In the in vivo trial, the efficacy of adsorption has to be determined by the animal performance (body weight gain, feed consumption and feed efficiency) and the target organ protection (TOP).
It is important to evaluate the TOP since it reflects the specific damage caused by the mycotoxin. It is also necessary because some adsorbents base their effectiveness on a positive change in performance or reduction of a secondary effect caused by the mycotoxin, which is a result of the presence of enzymes, beneficial bacteria, yeast and/or immuno-stimulant in the composition of those products, and not mycotoxin adsorption.
The relation between in vitro evaluation and in vivo effectiveness cannot always be confirmed. In evaluations done by Dr Mallmann and collaborators in LAMIC on 58 AMA for different toxins and species, little more than 55% of AMA approved in vivo, had an in vitro adsorption greater or equal to 90%. For AMA approved in vivo, more than 50% had an in vitro adsorption less than 70%. There was no significant correlation between in vitro and in vivo evaluations when the data of those 58 in vitro and in vivo evaluations were submitted to a linear regression analysis.
It is evident from this data that the results obtained from in vitro evaluations are not sufficient to prove the efficiency of an AMA. Therefore, statistical satisfactory results from the in vivo test are necessary to determine the efficacy of an AMA and only TOP products can be considered to have real protection.
Clays and their myths
During the last 25 years, various scientific studies have demonstrated that some aluminosilicates are very effective in preventing the damage of the most prevalent mycotoxin of the last century: aflatoxin. Three myths were created during the twentieth century: 1. Clays only adsorb aflatoxin, 2. High inclusion levels (5-20 kg/tonne) are needed, 3. Clays adsorb nutrients.
Today, science has disproven these three myths. There are few products that are also effective against other mycotoxins besides aflatoxin; they work at low dosage; and they do not adsorb nutrients, because they are not expandable clay. Among these, Myco- Ad is exceptional because it has been scientifically proven to have TOP results at 2.5 kg/tonne not only against aflatoxin, in poultry, swine and dairy cows; but also preventing the reduced performance and the organ damages caused by ochratoxin, T-2 toxin and fumonisin in broiler chickens, without adsorption of nutrients.
Special purified and activated phylosilicate have been developed in recent years. These products are capable at a very low dosage (0.5 to 2.0 kg/tonne) of binding fusariotoxins, the most predominant and difficult to control mycotoxins. Myco-Ad AZ, one of the few purified phylosilicates, has been scientifically proven to have TOP results against fumonisin, deoxynivalenol (Figure 1), and zearalenone (Figure 2) in pigs. Recently, Myco-Ad AZ also has shown to have TOP results against T-2 toxin in broiler chicks at 0.5 kg/tonne, without interfering with nutrient absorption. (Table 1)
From the above we may conclude that the effectiveness of an antimycotoxin additive has to be evaluated by conducting in vivo tests using a scientific experimental design which measures the beneficial effects of the product on target organ protection and animal performance.
[Source: Mycotoxin Special]