Mycotoxins are secondary metabolites produced by a wide variety of filamentous fungi, including species from the genera Aspergillus, Fusarium and Penicillium. The fungi typically grow on various feedstuffs, such as grains and cereals. Mycotoxins are invisible, tasteless, chemically stable, and survive high temperatures and many environmental conditions. Most animal feedstuffs are likely to be contaminated with multiple mycotoxins. The growth of moulds and mycotoxin production occurs worldwide, especially in climates with high temperatures and humidity and where grain is harvested with high water content. The Food and Agriculture Organization (FAO) estimates that as much as 25% of the world’s agricultural commodities are contaminated with mycotoxins, leading to significant economic losses.
The most common source of food and feed contamination are mycotoxins produced by the fungi Aspergillus, Penicillium and Fusarium genera. Other mycotoxin-producing fungi include Alternaria, Chaetomium, Cladosporium, Claviceps, Diplodia, Myrothecium, Monascus, Phoma, Phomopsis, Pithomyces, Trichoderma and Stachybotrys.
While Aspergillus and Penicillium species are generally found as contaminants in feed during storage, Fusarium and Alternaria species can produce mycotoxins before harvesting or immediately after. Every plant can be contaminated by more than one fungus, and each fungus can produce more than one mycotoxin. Up until now, approximately 400 secondary metabolites with toxigenic potential produced by more than 100 moulds have been reported.
Aspergillus, Fusarium, Penicillium and Claviceps produce the most extensively studied mycotoxins. Some of the mycotoxins produced by these moulds include aflatoxins, ochratoxins, deoxynivalenol (DON), T-2 toxins, zearalenone, fumonisins, Citrinin and ergot alkaloids. Mycotoxins cause diverse effects on animals, such as carcinogenesis, hepatotoxicity, and neurotoxicity, as well as impaired reproduction, digestive disorders, immunomodulation, and decreased performance.
Multiple factors determine the contamination of agricultural commodities with mycotoxins. Mycotoxin occurrence varies between crops, as fungal species and strains differ in their ability to infest a particular host. It also varies between varieties of the same plant species, as varieties show different levels of susceptibility or resistance to fungal infestation. Furthermore, environmental conditions, such as temperature and humidity, affect the infestation of crop plants with mycotoxigenic fungi and mycotoxin; therefore, climate and weather are strong determinants of mycotoxin contamination. Moreover, agricultural practices, the timing of harvest, and post-harvest handling of crops affect mycotoxin formation.
Crops may be infested with multiple strains of fungi, and most fungal strains produce more than one type of mycotoxin. Therefore, co-contamination of agricultural commodities with multiple mycotoxins is frequently observed. When feed raw materials are mixed, mycotoxin co-contamination becomes even more likely. If mycotoxins co-occur, their combined toxic effect may be much greater than the summed effects of the individual mycotoxins.