Beating in-feed aflatoxins in warmer climates

In an era of ever increasing volatility in raw material prices and availability, being able to secure sufficient raw materials of acceptable quality is becoming one of the main challenges for the livestock industry. In an effort to reduce feed cost and to obtain sufficient feed raw materials, livestock producers are often forced to make use of unconventional protein and carbohydrate sources or materials of lower quality. Changing climate conditions, such as extremes in temperature and precipitation or drought have their impact on quality parameters like bacterial counts, yeast, mould as well as mycotoxins, which are metabolites produced by moulds. Aflatoxins, produced by Aspergillus moulds, belong to the most toxic mycotoxins, which also show synergistic effects with most other mycotoxins.  Aflatoxins are most common in warm climates, especially in combination with drought and insect damage. Young animals are more susceptible than adults and amongst farm animals, poultry and ducks have the lowest tolerance to aflatoxins.  Feeding aflatoxin contaminated feeds can result in reduced growth performance, increased mortality, reduced vaccination efficacy and increased health problems. When performing necropsies, pale and enlarged livers are encountered.

Smectite clays

Since the late seventies it has been known that certain clay minerals bind aflatoxins and protect animals against the harmful effects in the intestinal tract. Amongst clay minerals, smectite clays and especially calcium smectite clays (Ca-smectites) have been found to possess the highest binding capacity and binding strength for aflatoxins.  This high binding capacity can be explained by their structure, which consists of layers ‘trapping’ aflatoxins in the interlayer space, but also resulting in a high surface area to allow for a high amount of active binding sites.

The high binding strength is a result of the mineral composition which allows the creation of strong complexes with aflatoxins.  Selectivity of Ca-smectites for aflatoxins is high, since the Ca²⁺ exchange cations are divalent (meaning they can form two bonds with other ions or molecules), making them bigger, which results in the optimal required remaining surface area for an aflatoxin molecule. For monovalent exchange cations like Na⁺, the remaining surface area is too small, making Na-smectites not ideal for aflatoxin binding. Furthermore, aflatoxins have not only one but two carbonyl groups, which allow them to form tight complexes with these divalent exchange cations as well as with Fe²⁺ and Al³⁺ which are part of the structure of the smectite layers but are free accessible at layer edges.

In vitro studies

Nutreco R&D conducted a series of in vitro binding studies to select the best smectite clays and found that an optimized mixture of specific Ca-smectites demonstrated the highest aflatoxin binding capacity. On the basis of this research, Selko Feed Additives developed Toxo-MX, that has a high ability to bind aflatoxins in particular, but also other mycotoxins like ergot alkaloids.

This mycotoxin binder was further tested and tried in a series of in vitro trials at different specialised and independent laboratories in the EU as well as in the US. The test methods determine the binding efficiency and maximum binding capacity, while mimicking the conditions in gastrointestinal tracts. In this method the adsorption is determined at pH 3 which is close to the pH of the stomach, followed by a desorption step at pH 7, simulating intestinal conditions. The efficiency is calculated as the percentage of adsorption minus the percentage of desorption.

Figure 1 displays the main results of the binding efficiency test. It can be seen that binding efficiency of the mycotoxin binder under different inclusion levels and aflatoxin B1 (AFB1) concentrations was always close to 100%.

Binding ergots

Ergot alkaloids are mainly produced by Claviceps moulds in more cool and moderate climates and can also be very harmful to all animal species, particularly ruminants. At high levels, ergot alkaloids can cause vasoconstriction and gangrene. They can also impair reproductive performance and decrease milk yield in dairy animals. Binding tests with different ergot alkaloids were conducted at three different pH conditions. The results in Figure 2 show that even at a very high pH, always more than 70% of each ergot alkaloid is bound.

Next to in vitro trials, the binder was tested in a study with broiler chickens fed, high levels of AFB1 at the Nutreco Poultry Research Centre in Spain. One day old broiler chickens were randomly distributed into three different dietary treatments fed either a control diet without AFB1 or a diet with 3 ppm AFB1 with or without 0.25% of the mycotoxin binder for three weeks. Feed intake and body weight were measured as well as relative organ weights, as

AFB1 also damages organ tissue and increases organ weight. During the three-week period, as shown in Figure 3, AFB1 significantly reduced weight gain and feed intake and had a negative impact on feed conversion ratio. The mycotoxin binder was able to significantly improve weight gain and feed intake and had a positive influence on feed conversion ratio.

Relative organ weights of the selected broilers are displayed in Figure 4. AFB1 significantly increased relative organ weights of gizzard, liver and kidneys. The inclusion of 0.25% mycotoxin binder led to a significant reduction in relative organ weights.

No nutrients bound

It is known that several clays do not only bind mycotoxins but can also bind nutrients, which of course is highly undesirable. For that reason a nutrient binding test has been conducted at a

specialised laboratory. The mycotoxin binder (20% and 50% respectively) was added to a commercial broiler premix, containing high levels of vitamins and minerals. All samples were extracted with HCl, to simulate gastric conditions. The analyses results were adjusted for dilution (with 20% and 50% mycotoxin binder respectively). The results showed that the binder does not bind nutrients and can safely be used in animal feed and premixes. It also has excellent free-flowing properties and can be applied as an anti-caking agent in premixes.