Mycotoxins: Regular feed samples tests essential

18-05-2016 | |
[Photo: Nico de jong]
[Photo: Nico de jong]

Moulds produce mycotoxins as a natural immune system. The presence of these mycotoxins may vary greatly since the development of moulds in the field (e.g. Fusarium spp.) or during storage (e.g. Penicillium, Aspergillus) depends on several factors. This makes it very difficult to estimate the exact extent of the damage caused. Therefore it is recommended to regularly sample the feed, both when fungal and/or mycotoxin contamination is expected and as a prevention tactic.

In general, environmental conditions – heat, water, and insect damage – cause plant stress and predispose plants in the field to mycotoxin contamination. However, weather conditions are difficult to control and a thorough monitoring of the crop should be applied to prevent these moulds. Because feedstuffs can be contaminated pre- or post-harvest, control of additional mould growth and mycotoxin formation is dependent on storage management. After harvest, temperature, moisture content, and insect activity remain the major factors influencing mycotoxin contamination of feed grains and foods. Storage conditions should be very well fine-tuned to avoid mould growth.

Adverse effects of mycotoxins

Intoxication with mycotoxins occurs by eating contaminated feed. Since mycotoxins are usually not degraded during digestion or temperature treatments, these compounds can accumulate to high doses in feed products, in this way forming a serious risk for animals. Many symptoms are associated with mycotoxin intoxication (mycotoxicosis), most of which are well described in animals. Mycotoxicosis can occur at 2 levels:

  1. acute illness due to intake of high levels of mycotoxins and
  2. chronic illness due to regular low level intake of mycotoxins.

Acute and chronic mycotoxin symptoms in animals

Symptoms of acute mycotoxicosis:
Nausea, vomiting, abdominal pain and diarrhoea.
Symptoms of chronic mycotoxicosis:
Reduced feed intake, reduced growth and development, suppression of the immune system, some types of cancer, foetal malformation, birth defects, disturbed embryonic development during pregnancy and toxic effects on fertility.

Because of the serious health risks, it is very important to monitor mycotoxin levels during the feed production chain. Monitoring involves a correct sampling method as well as an accurate detection technique.

Sampling: The start of a reliable assay

Moulds (and therefore also mycotoxins) never have a homogeneous distribution pattern. Often point source contamination occurs in the field or during storage. Therefore some parts of the feed or the raw material will be free of mycotoxins whereas other parts will have very high values. Traditional methods of sampling and sample preparation of agricultural crops are usually not adequate for mycotoxin analyses because mycotoxin contamination is usually heterogeneous, which creates problems in obtaining a representative sample for analysis. Therefore correct sampling is extremely important. The highly non-uniform distribution of mycotoxin contamination, requires a sampling plan that takes this heterogeneity into account (Figure 1). The number of incremental samples to be taken depends on the weight of the lot and kind of feed material that is sampled.

Figure 1- Correct sampling of materials potentially contaminated with mycotoxins.

Rapid and accurate mycotoxin assay

Methods using liquid or gas chromatography and electrophoresis are tedious, laborious, time-consuming, require sophisticated equipment and/or trained personnel, and cannot be used in situ. Therefore simple and reliable methods of analysis are needed within the feed industry for the purpose of internal control. Therefore the Nuscience laboratory has implemented Quantitox. This device uses a Rapid One Step Assay (meaning that preparation, incubation and reading are combined in the Quantitox) and is not only very reliable but also user-friendly. The analysis is based on quantitative ELISA techniques (Enzyme-Linked Immuno Sorbent Assay) and is capable of quantifying the following 6 mycotoxins: fumonisin, DON, OTA, aflatoxin, ZEA and T-2 toxin. ELISA is an immunochemical reaction and is based on the specific binding between an antigen (e.g. mycotoxin) and an enzyme-labelled antibody (present in the Quantitox strip). Mycotoxins are detected through binding of the mycotoxins to the labelled antibodies. This means that they are chemically linked and create a colour after a few intermediate steps. The more of the substance to be detected (e.g. mycotoxin) was present, the more enzyme action, and the more colour is finally created. The colour is measured using an ELISA reader based on a spectrophotometric determination. This reader will pass a value to the Quantitox which will show a quantitative analysis of the amount of mycotoxin present. The Quantitox performs assays of both raw materials and complete animal feed. The only exception to this are silages. Their low pH affects the assay process.

Problems can occur below permitted mycotoxins levels

In the EU and elsewhere, guidelines have been set on maximum allowable mycotoxin content in feed and feed materials. In practice however, problems of mycotoxicosis often already occur below these guidelines. There are several plausible explanations for this. On the one hand, a mycotoxin is rarely present on its own and, moreover, a combination of different mycotoxins can have a synergistic effect. On the other hand, plants are capable of rapidly modifying some mycotoxins. These modified (masked) mycotoxins often escape assays but are converted into harmful precursors again in the animal. Finally, the effect of a mycotoxin will depend very much on the general immunity and stress level of the animal. All this together results in the practical maximum values being 2 to 5 times lower than the official guidelines, depending on the toxin and animal species (Table 1).

3-fold strategy

Therefore action needs to be taken when mycotoxins are demonstrated or fungi are present in the feed. Removal of the contaminated feed is often not the most economical solution. The qualitative and quantitative determination of the mycotoxin contamination level enables to choose the optimum Vitafix toxin binder and its optimal dosage. A good mycotoxin toxin eliminator combines three strategies for countering the mycotoxins. Activated and purified aluminosilicates should ensure a wide adsorbing range leaving essential nutrients unaffected. Since not all mycotoxins can be bound, also a biotransformation strategy is needed to transform these mycotoxins into harmless metabolites. Finally the use of supporting agents like betain and natural antioxidants can help reducing the negative effects of mycotoxins and promote recovery of affected organs. Regularly monitoring feed and consequently dealing with mycotoxins results in healthy animals, leading to increased production results and therefore better economic results.

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