Attapulgite-A unique clay for better digestion

By Dr Nicolas Theophilou, feed 
development director Geohellas SA, Greece

Clays are known for their layered structure and surface properties, making them ideal ‘sponges’ for unwanted molecules. The same applies to attapulgite clay. This clay is recognised for its ability to strongly interact with bacterial toxigenic strains of E. coli and Clostridium perfringens.  Products containing this type of clay can therefore be seen as natural alternatives for a healthy and efficient production, mainly because they benefit the animal by protecting the intestinal epithelium cells and a better digestion.
Different than other clays
This type of clay is different than other clays (e.g. montmorillonite or bentonite). The difference is in the structure, but also in physicochemistry. Montmorillonite belongs to the phyllosilicates smectite group with 2:1 structure (2 tetrahedral sheets of Silicon, sandwiching a central octahedral sheet of aluminium). Such lamellar structure opens up and swells in presence of water. Attapulgite has a nano tubular structure (Figure 1) with tubules having a 2:1 structure connected in the four edges and forming a stable non- swellable 3d network, leaving between the nanotubules 4-5 Å wide channels, offering to the mineral a great internal porosity 200-300 m2/g responsible for the very important water absorption capability of attapulgite. Therefore during the digestion process (intestinal tractus), attapulgite is absorbing internally and stabilising excess produced water whereas montmorillonite is trapping water externally between lamellas and swells creating a muddy mass. Surface properties of the two minerals do differ (presence of Si-OH groups on the surfaces of tetrahedral sheets of silicon that are interacting with toxins) due to different stereochemistry and different isomorphous substitutions of Mg for Al creating different surface charges in the two minerals.

Extrusion techniques

Attapulgite has been used in several industries for many years because the clay has a broad spectrum of uses. Major deposits exist in regions, including the state of Georgia in the United States, but also in Greece. Companies can extract it with surface mining techniques and process it in a variety of ways, depending on how it will be used, the clay can be divided into three different generation (see box on page opposite). At Geohellas in Greece, the industrial production process involves exfoliation of the bulk structure of the clay by using extrusion techniques. This way the internal specific surface of the mineral is increased, hence increasing the water absorbing capacity (anti-diarrhoeal effect). At the same time, thermal activation of the clay by using temperatures higher than 250 degrees Celsius creates a dry structural acidity level and enhances the surface organophilicity/ oleophilicity. This is the affinity of a surface to interact with organics such organic molecules (aflatoxins, mycotoxins etc). Oleophilicity is the opposite of hydrophylicity, means that a highly hydrophilic surface has a minimum oleophilic effect and also a highly oleophilic surface has a minimum hydrophilicity. In the case of attapulgite, there are internal porous surfaces that are 
hydrophilic and are trapping water, whereas external particle surfaces through short thermal treatment are becoming oleophilic to bind the toxins and bacterial toxigens. The reason that a non excessive temperature and a short treatment time is used is to keep the hydrophilic behaviour in attapulgite channels. This improves interactivity of the mineral with molecules such as mycotoxins and microbial pathogens.

Healthier gut in piglets

To test the ability to increase health and microbial infestation in piglets, a trial was carried out. Intestinal cells of piglets were inoculated with E. coli 0157:H7. Some intestinal cells of animals also received the feed with attapulgite (corresponding to a dosage in feed of 3 kg/mt), at several dilutions (10, 102, 104 and 106). Some piglets were given the normal feed, without the clay minerals. It was shown that attapulgite appears to have a protective action in comparison to the control group, shown in a 21% increase in the number of surviving intestinal cells in the presence of E. coli (10/ml) and a 13% increase at the highest concentration (106/ml). Similarly, the number of surviving cells in the presence of Cl. perfringes increased by 13% at the lowest concentration (10/ml) and 9% at the highest (106/ml).

Less diarrhoea

The Veterinary School of University of Bologna looked at the anti-diarrhoea effects of the clay in weaning piglets. Attapulgite, like other clays, are used to improve the technological characteristics of feed e.g. pellet hardness and durability or free flowing properties. They made two different diets for first and second weaning period, optimised for pellet quality and containing the clay. The control diet contained no clay. The clay was used in at a dosage of 1.5 % (e.g. 15 kg/mt of feed). In the first weaning period the pellet durability (a measure of the effectiveness of the pelleting process) (pellet quality) was optimised from 95.4 to 95.7 %. The hardness of the pellets in the same period was optimised from 1.7 to 3 kg. For the second weaning period the pellet durability versus control was optimised from 95.4 to 96.7 %, whereas the pellet hardness from 2.1 to 2.9 kg. A group of piglets (n=102) also received a control diet (without clay and not optimised for pellet quality). The first trial (n=102) showed that the total diarrhoea cases reduced from 19 to 8. Of these 8 cases, 87.5% had a mild form of diarrhoea and 12.5% a medium case. Mild and medium forms of diarrhoea in the control group were 36.8 and 63.2 % respectively. In the second trial (n=52), the total number of diarrhoea cases was reduced from 12 to 4. These four cases all had a mild form of diarrhoea. Mild and medium cases of diarrhoea in the control group were 33.3 and 66.6 % respectively. The researchers also noted a daily weight gain increase in the first trial (417 to 445 g/d) and second trial (435 to 471 g/d). Feed conversion ratio was improved from 1.83 to 1.67 (trial 1) and from 1.83 to 1.61 in trial 2.

Reducing veterinary costs

The beneficial properties of the clay on the intestinal health are also reflected in less veterinary costs, as shown at various pig farms in Brittany (France). 
This is the result of a better health status (less bacterial toxigenic strains and toxin manifestation in the gut) and an optimised digestive function of the animals. Data from these farms show a drop of mortality from 1 to 0.7 % in the weaning period (reduction of 0,3 % in mortality). In the weaning to slaughter period, a drop of mortality from 4.8 to 3.5 % was observed (reduction of 1.3 % in mortality). At the same time, antibiotics costs were reduced from 148 to 125 euro per sow per year. 
Feed conversion ratio dropped from 2.65 to 2.57 and daily weight gain improved from 667 to 690 g/d.

Improvement in broilers

Similar positive effects have been seen in broilers. In week 42 of last year, broilers (from day 0 to day 38) were fed third generation attapulgite. These birds were compared to birds in weeks 41 and 43 (chickens that did not receive the product). Mortality and final weight were the key parameters in the improvement of EPEF (European Production Efficiency Factor). The EPEF of the broilers fed with the clay reached 306, versus 278 (week 41) and 293 (week 43). A first generation attapulgite clay was also tested in broilers by the Agricultural University of Athens. 
They found optimised pellet characteristics, better health status of the birds and reduced mortality levels (7 to 3.5%).

Conclusions

Attapulgite products are used more and more by feed producers, integrators and farmers for their multifunctional innovative actions, on adsorption of microbial enterotoxins, mycotoxins and decomposition products of proteins. They clean the digestive system of the animals and hence improving the feed efficiency and farm profitability. Especially for young animal diets, the attapulgite clay can be of great interest.

[Source: AllAboutFeed Vol 22 nr 7, 2014]

References are available on request.