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ANCO knowledge: 3 things to know about bentonites

Bentonite can be applied in animal nutrition to adsorb mycotoxins and reduce mycotoxin bioavailability from contaminated feeds in the animal’s gut. It is a fine clay material mined from the earth. Most bentonites are formed by the alteration of volcanic ash in marine environments and occur as layers sandwiched between other types of rocks (as can be seen in the image above).

Bentonite is defined as a naturally occurring material that is composed predominantly of the clay mineral smectite. The Cation Exchange Capacity (CEC) and the specific surface area of smectites are considerable larger than other families of clays. Their absorption capacity is as much as 8 times greater than other clays.

However, there are a few things to know before applying bentonite to animal feed:
1. Not all bentonites are the same
2. Best proof of efficacy is still in vivo
3. Only one type of bentonite is EU approved for the adsorption of mycotoxins

1. Not all bentonites are the same

Bentonites are colloidal and plastic clay materials composed largely of montmorillonite (a species of dioctahedral smectite). The properties of bentonites can vary considerably depending on geological origin and any post-extraction modification. Their individual characteristics have a marked bearing on their economic use.

Despite the generic nomenclature of commercially-available bentonite, several physicochemical properties have been identified as having a possible correlation with adsorption of mycotoxins and might therefore be used to categorize the different available types.

These characteristics comprise:
• cation exchange capacity (CEC), exchangeable K+, Na+, Mg++ and Ca++,
• pH
• linear swelling,
• mineral fraction
• relative humidity
• d-spacing

Role of d-spacing for zearalenone adsorption

Adsorption to clays is not limited to the surface of the clay particles, but extends also to the interlayer space of the clay. This interlayer space, characterized by the d-spacing, can be determined with X-ray diffraction (XRD) and is restrictive for the formation of one or more adsorbent layers. This space can increase if the clay swells, thereby increasing the number of binding sites.
In vitro adsorption tests have shown that there is a positive correlation between zearalenone adsorption and d-spacing in commercially available products based on bentonite, i.e. large d-spacing was associated with higher % adsorption of zearalenone. (De Mil et al 2015). The d-spacing ranged from 9.2 to 21.5 (10-10 m) in 16 different products containing bentonite material, showing the large variation in material out there.

Difference between cis- and trans-bentonites for aflatoxin adsorption

Recent scientific data (Vekiru et al 2015) evaluating different types of bentonites for the in vitro adsorption efficacy relating to aflaxtoxin B1 has shown that most of the tested Ca- or Na-bentonites were effective. However, cis-bentonites were more effective than trans-bentonites.
Dioctahedral smectites that are found in bentonite have one vacant position in the octahedrons because one of the three symmetrically independent octahedral positions is not occupied by cations, resulting in a vacant site. The disposition of the hydroxyl groups in the octahedral sheet with respect to this vacancy defines the configuration cis- or trans-vacant.

2. Best proof of efficacy is still in vivo

In vitro experiments have been developed as a way to effectively pre-screen adsorption agents before testing in animals. However, results between in vitro and in vivo efficacy can vary significantly. Even among bentonites with high in vitro adsorption efficacy, there are differences in in vivo efficacy indicating that in vitro testing alone is not adequate for evaluation of adsorbents.

3. Only one type of bentonite is EU approved for the adsorption of mycotoxins

Currently 1m 558 bentonite has been approved as a substance for reduction of the contamination of feed by mycotoxins (aflatoxin B1) for pigs, poultry and ruminants according to EU regulation in the EU register for feed additives. The approval is based on safety of using the product and proven in vitro and in vivo adsorption efficacy of Aflatoxin.

This bentonite meets the following characteristics:
• Bentonite: ≥ 70 % smectite (dioctahedral montmorillonite)
• < 10 % opal and feldspar
• < 4 % quartz and calcite
• AfB 1-binding capacity (BC AfB1) above 90 %

At current recommended maximum inclusion level of this bentonite in animal feed, the binding of vitamins and minerals is insignificant.

Read ANCO’s first publication in All About Feed, June 2016

As plants evolved, they developed very sophisticated coping mechanisms to stressors, helping plants to be more agile in the face of stressors and threats to survival. It is therefore right to think that new agile concepts developed for nutritional strategies to empower animals to adapt to stressors rely partly on the power of plants.

Several meta-analysis studies have proven the negative impact of mycotoxins in pig and poultry diets on animal performance. What is also becoming apparent with greater knowledge of the impact of mycotoxins on animals is, that mycotoxins will cause very similar physiological and metabolic reactions in the animals as seen in response to more common stressors. Those reactions will again increase cell damage, waste metabolic energy, increase the susceptibility to disease and reduce appetite. Through a multitude of bioactive substances, with a variety of adaptive properties plants are very well equipped to be polyvalent to different stressors and to prevent their negative impact. Bioactive substances derived from plants have also shown to support humans and animals to adapt to stressors more adequately and help counteract some of the negative physiological and metabolic side effects. Applying the right combination of plant extracts to feed can therefore help the animal become more robust and reach performance potential more efficiently in the face of stressors, including mycotoxins.

Read more in Disarm mycotoxins with the agile power of plants, by Gwendolyn Jones, June 2016 digital All About Feed issue, Vol 24/5, page 24-26
http://www.allaboutfeed.net/All-About-Feed-Digital-Magazine/