Mycotoxins are secondary products of fungal metabolism that may be produced in contaminated feeds during production and storage. It has been estimated that at least 300 fungal metabolites are potentially toxic for man and animals, and that as much as 25% of the world's cereal grains are contaminated with measurable levels of mycotoxins (Devegowda et al., 1998). Fungal growth in silages, stored forages and byproducts can result in toxin formation. As a result, mycotoxins can be found in many types of feed materials and are commonly encountered in livestock production systems. As a group, mycotoxins are chemically diverse and have a broad range of physiological activities in animals. These toxins are typically present at low concentrations, even in highly contaminated feeds. However, many are produced at concentrations known to have significant effects on animal health and may have a major impact on animal production. The negative influence on the growth and health of livestock makes them a major problem in many production systems.
The fungi in the Fusarium species produce more than 100 metabolites that are potentially toxic in animals. These include trichothecenes (deoxynivalenol, T-2 toxin, HT-toxin and diacetoxyscirpenol), zearalenone, fumonisins, moniliformin and fusaric acid. It is unlikely that any one of these toxins would be produced individually in great quantities. As a result, toxicosis associated with these fungi is often a complex process involving a number of toxins (Smith et al., 2000). The fusarium toxin, deoxynivalenol (DON), is known for its ability to inhibit protein synthesis and has been shown to incrementally decrease intake in pigs at concentrations above 2 ppm (Newman, 2000). It can also influence reproductive performance and is associated with immunosuppression (Johnson et al., 1997). T-2 and related toxins can cause irritation and hemorrhages in the gastrointestinal tract. In severe cases, T-2 causes oral lesions in poultry and swine. Zearalenone is known for its estrogenic activities and its ability to impair reproductive performance. At low concentrations it influences the development of reproductive organs and causes rectal and vaginal prolapses. Fumonisin is known for its ability to impair immune function and cause kidney and liver damage. As a result, it can have a significant impact on animal performance and the incidence of disease in many species.
Ways to control mycotoxins and mycotoxicosis
A number of approaches have been used to control the adverse effects of mycotoxins in animal production systems. Many of strategies are to prevent the growth of fungi and the formation of toxin by altering feed management practices. Strategies that use microbial or thermal inactivation of toxins, physical separation of contaminated feedstuffs, irradiation, ammoniation and ozone degradation have all been examined as tools for destroying or modifying mycotoxins (CAST, 1989; McKenzie et al., 1998). However, these strategies tend to be costly or time consuming and have not been found to be of practical use.
A number of strategies are based on nutritional manipulation that can help overcome the toxic effects of ingested toxins. These strategies are based on the fact that many subtle effects of mycotoxins can be overcome by maintaining animals in a healthy, disease-free environment using antioxidants for example. However, most studies of these potential strategies have been performed in basic biochemical test systems, and it is not clear how the protective effects of such strategies can be used to define nutritional approaches for control of mycotoxin-associated toxicosis. As a result, such strategies have not become widespread practical applications in animal production systems.
Another approach for attenuating the effects of mycotoxins is based on the use of specific materials that adsorb mycotoxins in animal feeds. These have become some of the most practical methods for controlling mycotoxins in feeds. They are based on the ability of the adsorbents to 'tie up' or 'bind' the toxins. This allows the toxins to pass through an animal's digestive tract without being absorbed. Both inorganic and biological adsorbents have been examined and used to control the bioavailability of mycotoxins.
Inorganic clay-based adsorbents and activated charcoal have been shown to adsorb specific mycotoxins and are attractive as feed supplements because they are relatively inert from a nutritional standpoint. These include hydrated sodium calcium aluminosilicates (HSCAS), zeolites, bentonites, specific clays and activated charcoals prepared from different sources (Piva et al., 1995).
Clinoptilolite, which in Greek means 'oblique feather stone', is a member of the zeolite group of minerals (Harben, 1999). Clinoptilolite is a naturally occurring zeolite, formed by the devitrification of volcanic ash in lake and marine waters millions of years ago. It is the most researched of all zeolites and is widely regarded as the most useful. Clinoptilolite is able to bind a range of mycotoxins, forming highly stable complexes (Tomasevic-Canovic et al, 2001; Huwig et al, 2001). Studies have shown that clinoptilolite absorbs toxins created by moulds in animal feeds, as well as enhancing nutrient absorption by cattle, pigs, lambs and other animals. Clinoptilolite binds a range of mycotoxins, which is a benefit to the health of animals into whose feed clinoptilolite has been added (Huwig, 2001; Phillips, 1990).
There has been a great deal of interest in using natural biological products to reduce the bioavailability of mycotoxins in animal production systems. One available strategy for attenuating the effects of some groups of mycotoxins uses the unique adsorptive capacity of the carbohydrate complexes in the yeast cell wall. Yeast cell wall has various effects, like improving nonspecific immunity, increasing resistance to infection, adsorbing mycotoxins and regulating the micro-environment of an animal’s digestive tract.
Yeast cell wall is composed of complex polymers of β-(1,3)/(1,6) glucan, mannan-oligosaccharide (MOS) and chitin. β-glucan, as an immune modulator substance, is able to stimulate non-specific and specific immunological response, activate T cells, B cells, macrophages and natural killer (NK) cells, boost resistance to disease, and thus improve the production performance of animals.
As a mycotoxin binder, yeast cell wall has numerous characteristics as follows: Binding mycotoxins, especially zearalenone (ZEN); unaffected by the pH of the gastrointestinal tract; without changing nutritional value (regarding mineral and vitamin) in feed; no residue in animal and no negative effect on human health.
Mycotoxins and their associated health problems are common in modern livestock systems. Adsorbents that bind mycotoxins and decrease their bioavailability show a great deal of promise as tools for use in strategies that attenuate mycotoxin-induced toxicosis. The high affinity and high adsorption capacity of yeast-derived glucomannan preparations and clinoptilolite make their use as adjuncts for controlling naturally occurring mycotoxins in feeds attractive. Also beta glucan can be a good way to decrease mycotoxin consequences leading to a better immune system in the animal body.
Soruce1: Understanding the adsorption characteristics of yeast cell wall preparations associated with mycotoxin binding
Published on: 10/2/2006
Author/s : KARL A. DAWSON, JEFF EVANS and MANOJ KUDUPOJE - Alltech Inc.
Source 2: Available solutions for mycotoxin binding
Published on: 4/15/2010
Author/s : Matt Pearce BSc.(Hons)Msc., Dr Inga Shahin MRCVS, Daniel Palcu BSc,MSc.
Source 3: Application of yeast cell wall in swine
Author/s: Li Biao technical manager Angel Yeast, China