A proven successful approach to managing mycotoxins
Controlling mycotoxins is not an easy task. A number of approaches have been tried, but because of the large number of toxins that exist and their interactions, a single solution to the problem does not exist. Research shows that combining selected adsorbents with bio-transformation methods will ensure effective protection in mycotoxin-contaminated feeds.
Mycotoxins are toxic secondary metabolites of various fungi, mainly those belonging to the genera Fusarium, Aspergillus and Penicillium. There are hundreds of mycotoxins known, but few have been extensively researched and even fewer have good methods of analysis available. The major classes of mycotoxins, in terms of agricultural relevance, are aflatoxins, zearalenone, trichothecenes (e.g. deoxynivalenol, T-2 toxin), ochratoxin A, fumonisins and the ergot alkaloids. Their global occurrence is considered to be a major risk factor, as according to the Food and Agriculture Organization (FAO) as much as 25% of the world's crops are affected annually despite increased efforts of prevention.
Mycotoxins exhibit a great variety of biological effects in animals: specific tissue damage, central nervous system effects and digestive disorders, to name a few. However, mycotoxin-related losses in performance, reproductive disorders and immune-suppression, resulting in a higher susceptibility to disease, are of major concern.
The ever-increasing number of reports on the presence of mycotoxins in foods and feed dictates the necessity for practical and economical detoxification procedures. A number of physical and chemical approaches have been taken to counteract mycotoxins, though only a few have real practical application.
The efficacy of physical treatments (e.g. washing, separation, roasting, UV irradiation, solvent extraction) depends on the level of contamination and the distribution of mycotoxins throughout the grain. Subsequently, the results obtained are uncertain and often connected with high product losses. Furthermore, some of these physical treatments are relatively costly and may remove or destroy essential nutrients in feed.
Chemical methods require not only suitable reaction facilities but also additional treatments (drying, cleaning) that make them time consuming and expensive. Only a limited number of tested chemicals are effective without diminishing the feed's nutritional value or palatability. Treatment of contaminated feed with ammonia was once the most attractive method. Although early studies showed this technique to be safe and effective, ammoniation has not been approved by the US Food and Drug Administration due to the potential toxicity and carcinogenicity of the resulting products.
Adsorbents successful against aflatoxicosis
The high costs and limitations of physical and chemical treatments prompted a search for other solutions to the mycotoxin hazard. Consequently, techniques based on deactivation of mycotoxins in vivo have been investigated.
Up to now, the most widely investigated method in this field is the addition of chemisorbents with the capacity to tightly bind and immobilise mycotoxins in the gastrointestinal tract of animals, resulting in a major reduction in toxin bio-availability. In several studies, hydrated sodium calcium aluminosilicates (HSCAS) have proven to be the most promising adsorbents. However, while good and scientifically explained results were obtained for counteracting aflatoxins, absorption of other mycotoxins was limited (e.g. zearalenone, ochratoxin A) or even failed under field conditions (e.g. trichothecenes such as DON).
Biological detoxification of trichothecenes proven
For the less- and non-adsorbable mycotoxins, an alternative practical method had to be found. Enzymatic or microbial degradation of mycotoxins ("biotransformation") leading to non-toxic metabolites has already been a subject of research for more than 30 years. A great deal of literature is available concerning the biotransformation of trichothecenes, among the world's most important agricultural toxins. It is well known today that the 12,13-epoxide ring is responsible for trichothecenes' toxicity and that reductive de-epoxidation entails a significant loss of toxicity (figure 1).
Although several microorganisms with mycotoxin degradation activity have been isolated in the past, the Austrian company Biomin was the first to develop and patent a mycotoxin-deactivating feed additive based on live microbes.
A safe bacterial strain was found to have trichothecene-detoxifying activity and was named Eubacterium BBSH 797 after Biomin's research team that discovered it in July 1997: Binder, Binder, Schatzmayr and Heidler (figure 2).
Fig. 2: Electron micrograph of BBSH 797.
During its metabolism BBSH 797 produces specific enzymes that eliminate toxicity of trichothecenes by selective cleavage of their toxic 12,13-epoxy group (figure 1). Studies using in vitro models with pig and chicken intestine revealed that BBSH 797 exhibits activity in the gastrointestinal tract of monogastric animals and can therefore be used as feed additive for pigs and poultry to detoxify trichothecenes in the gut. In order to prove the in vivo efficacy of BBSH 797, scientific feeding trials were conducted at the University of Veterinary Medicine in Vienna, Austria. Highly significant results (p<=0.001) were obtained in piglet feeding trials using feed contaminated with 2.5 ppm DON (table 1).
In broiler trials, a mycotoxin concentration higher than that found under field conditions was used in order to obtain sufficient performance reduction (10.5 ppm DON). However, even at such high levels of contamination, addition of BBSH 797 reduced mortality from 19.4 to 5.5% and had a significantly (pÂ£0.05) positive influence on the weight development of the birds. The average final weight in the control group (no BBSH 797 added) was 1257.8 g compared to 1437.2 g in trial group (BBSH 797 added).
Fig. 3: Light microscopic picture
OTA and ZEA detoxifying agent of T. mycotoxinivorans.
A very recent development has been made by Biomin in the fight against ochratoxin A (OTA) and zearalenone (ZEA). During a several-year research project numerous bacteria and yeast species were screened for their mycotoxin-degrading ability. At the end of a very comprehensive selection process, considering features like detoxification-velocity, pathogenicity, ability to work under gastrointestinal conditions, the possibility of industrial scale fermentation and stabilization, a new yeast species belonging to the genus Trichosporon came out on top (figure 3). It was named T. mycotoxinivorans after its unique property to "eat" and thus detoxify both, OTA and ZEA (lat.: vorans = eating, devouring).
Incubation experiments with T. mycotoxinivorans proved successful detoxification of 1 ppm zearalenone (figure 4). Subsequent tests with animal cell cultures carried out at the University of Utrecht in the Netherlands showed that ZEA-containing broth incubated with the yeast strain does no longer have estrogenic activity.
Fig. 4: Degradation of ZEA (retention time 7.45 min) by T. mycotoxinivorans
A feeding trial conducted at the University of Maribor in Slovenia revealed that the negative influence of high OTA-doses (1 ppm) on the performance of broilers could be totally neutralized by addition of T. mycotoxinivorans. The final weight of the trial group (toxin and yeast added) was on average 83 g higher than that of the positive control (toxin, no additive) and even better than the negative control (figure 5).
Fig. 5: Broiler trial - In vivo detoxification of OTA by T. mycotoxinivorans
In vivo activity of T. mycotoxinivorans in piglets was investigated at the University of GÃ¶dÃ¶llÃ¶ in Hungary. Addition of the yeast strain to the diet clearly improved weight development and feed conversion rate of animals (table 2). Moreover, animal losses and cases of diarrhea were lower in control and trial groups (A, C, D, E, F) than in the toxin group (B).
The isolation and characterization of microorganisms that are able to bio-transform mycotoxins in the intestinal tract of animals is probably the breakthrough for a successful mycotoxin control. The biological methods described above may become the technology of choice, as enzymatic reactions offer a specific, irreversible, efficient and environmentally friendly way of detoxification that leaves neither toxic residues nor any undesired by-products. Research teams working in this field are convinced that combination of selected adsorbing agents and bio-transformation methods will ensure an effective control against mycotoxins taken in with contaminated feeds.