Six toxins, two moments and one conclusion: you cannot tell by looking at the grain.
Mycotoxins are secondary metabolites of moulds. They are not a sign of spoilage and do not disappear when the mould dies: they remain in the grain, even after drying, milling and processing. This makes them difficult to control with measures that rely solely on sight or smell.
Fusarium species infect the plant during flowering, particularly in wet weather and moderate temperatures. The toxins that result from this — DON, zearalenone, T-2/HT-2 and fumonisin — are already present in the grain before it leaves the field. In contrast, Aspergillus and Penicillium thrive during storage and transport, at moisture levels above approximately 14% and sufficient heat. That is where aflatoxin and ochratoxin A develop.
| Toxin | Mainly in | Critical for | Primary effect |
|---|---|---|---|
| Aflatoxin B1 | maize, nuts, imports | dairy cattle, poultry, humans | liver damage; carcinogenic |
| DON | wheat, maize, DDGS | pigs | feed refusal, vomiting, growth depression |
| Zearalenone | maize | pigs, especially piglets | oestrogenic effects, fertility |
| Fumonisin | maize | horses, pigs | leukoencephalomalacia, pulmonary oedema |
| Ochratoxin A | barley, oats, storage | pigs, poultry | nephrotoxicity |
| T-2/HT-2 | oats, barley | poultry, pigs | feed refusal, immune function |
Classification based on the EFSA risk assessments underlying the current standards.
Fungi that strike in the field often produce more than one toxin, and a lot is usually a mixture of plots, varieties and harvest dates. A sample containing DON therefore frequently also contains zearalenone; maize with fumonisin can also contain aflatoxin. Which combination is present in your lots depends on the crop, origin and the weather that season.
The same lot can be acceptable for cattle and unusable for pigs. DON has a guidance value of 5 mg/kg for cattle and 0.9 mg/kg for pigs. Zearalenone is set at 0.5 mg/kg for dairy cattle and 0.1 mg/kg for piglets. Fumonisin is set at 5 mg/kg for horses and 50 mg/kg for adult ruminants. Those differences stem from toxicology, not from trade.
In addition to free toxins, bound and masked forms exist, such as DON-3-glucoside. These are not routinely included in the analysis and fall outside current maximum levels: in 2024, the Commission explicitly stated that there is not yet a routine method to set standards for the sum of DON and its modified forms. In practice, this means that the measured value is a lower bound, not a total.
The conclusion is therefore simpler than the chemistry: you cannot see mycotoxins on the grain, you cannot dry them away, and you cannot cover them with a single test. What remains is a system of representative sampling, targeted testing and applying the right standard to the right destination.
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