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Mycotoxins in pig production. Definition, classification and toxic effects

Given the complexity of the problem caused by mycotoxins in pig production, we must come up with a preventive strategy in order to attain a contamination level that is as low as possible.

1. Definition

Mycotoxins are organic chemical compounds with a low molecular weight and a great stability with respect to pH conditions and temperature. Currently, some 500 different mycotoxins are known.

They are produced by toxigenic strains of moulds that contaminate the raw materials during their cultivation and/or storage. They are secondary metabolites that are only produced under certain environmental conditions that stress the mould (CO2, O2, concentration of minerals, temperature, water activity, pH, etc). The genera Fusarium, Aspergillus and Penicillium are the main culprits, although Claviceps, Alternaria, Cladosporum and Dreschlera can also appear as producers of mycotoxins. These moulds genera are famous for their ubiquity.

Their stability and the fact of being secondary metabolites are factors that are responsible that high levels of mycotoxins may be found in raw materials that are not very contaminated by moulds, because they remain even though the moulds disappear; as well as the fact that high levels of mycotoxins may not be found in raw materials with high levels of mould contamination, because the conditions for the production of mycotoxins may have not been met, or because these moulds may not belong to toxigenic strains.

Currently, they entail the main danger for the swine production and feeding sector in terms of human food safety because of the probability of its appearance and the seriousness of the direct effects (financial losses related to the drop in production) and the indirect effects (presence of mycotoxins in animal tissues). The hazard due to mycotoxins has been identified as an emerging potential hazard by the EFSA, and some of the predisposing factors for this increase in the incidence are the ones shown in Fig. 1.

Main predisposing factors for contamination with mycotoxins

Fig. 1. Main predisposing factors for the contamination with mycotoxins.

2. Classification

The classification mostly used has been the one based on the mould that produces the mycotoxin and/or the stage of the production of the mycotoxin, whereas in the field or during storage, but as investigations in this field progress, we discover that this classification is too flexible, because a genus can produce several kinds of mycotoxins, and it can do it in the field as well as during storage. Currently, the classification used is based on the chemical structure and polarity, and there are seven groups (Fig. 2):

Figure 2. Groups of mycotoxins according to their chemical structure

GROUP Mycotoxins Main moulds that produce it Chemical structure
Aflatoxins Aflatoxin B1
Aflatoxin B2
Aflatoxin G1
Aflatoxin G2
Aspergillus sp Dihydro or tetrafurans
Ochratoxins Ochratoxin A
Ochratoxin B
Aspergillus sp
Penicillium sp
Isocoumarin derivatives
Trichotecenes
Type A
DAS, T2, TH-2, etc… Fusarium sp Tetracyclic skeleton
Type B DON, nivalenol, etc…
Fumonisins Fumonisin A
Fumonisin B
Fusarium sp Hydrocarbon chain
Zearalenone Zearalenone Fusarium sp Macrocyclic lactones
Alcaloids Ergot, etc… Claviceps sp Alcalenes
Others Patulin, Roquefortine, etc.. Penicillium sp Various

3. Toxic effects

The toxic effects are determined by the ingested dose, the length of exposure, the interaction with other toxic substances and the genetic susceptibility of the individual. These effects on the animals' health are called 'mycotoxicosis', and they can be clinical or subclinical, and acute or chronic. The affected organs are mainly those that are responsible for the metabolism (liver, kidneys and lungs), but they also affect the central nervous system, the immune system and the reproductive system.

Although in pig production acute clinical effects on the digestive and immune systems are especially important (weight loss, predisposition to infectious diseases, etc…), as well as those related to reproduction (abortions and infertility, weak piglets, etc…), we must not forget the importance of the subclinical chronic effects (increase of the feed conversion rates, predisposition to infectious diseases, reduced longevity of the sows and boars, etc…), which entail a continuous loss of production efficiency, genetic potential and profitability of the farm.

Sometimes the laboratory results obtained after the appearance of a problem in which we suspect the presence of mycotoxins do not match with the observed clinical effects, and this is mainly due to the factors summarized in Fig. 3

related to the variability of the clinical effects and the laboratory results

Fig. 3. Factors related to the variability of the clinical effects and the laboratory results.

The European Commission and the animal feeding sector work together gathering information related to the presence of mycotoxins in raw materials for establishing maximum limits or recommendations. Whilst they are officially established, the practical reference levels used for the main mycotoxins that affect swine appear in Fig. 4.

Fig. 4. Reference levels of the main mycotoxins that affect swine

Mycotoxin Maximum level (ppb) Alert level (ppb)
DON 900 250
T2 1,000 50
DAS 2,000 50
ZEA
Piglets and gilts
Fattening pigs, sows and boars

100
250

100
250
OCRA A 50 25
FUM (B1+B2) 5,000 2,500
Aflatoxin 20 20
Ergot 6,000 500

The EU regulations that are to be applied regarding mycotoxins are (Fig. 5):

Fig. 5. Reference regulations regarding mycotoxins

Maximum levels Sampling and tests
Directive of the European Parliament and the Congress 2002/32/CE of May 7th 2002 about undesirable substances in animal feeding (and modifications). Regulation of the European Parliament 401/2006 of February 23rd 2006 that establishes the sampling and testing methods for the official control of the contents of mycotoxins in food products.

Given the complexity of the problems due to mycotoxins in pig production, a preventive strategy must be assumed in order to try to achieve an ALARA (as low as is reasonably achievable) contamination level using the principles reflected in Fig. 6, because the current decontamination systems do not have a good cost-effectiveness, and in Europe, the 'dilution' of raw materials and contaminated feeds is forbidden.

Prevention strategy against mycotoxicoses in pig production

Figure 6. Prevention strategy against mycotoxicoses in pig production.

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