Number one, as they are not homogeneously distributed within the lot, mycotoxins tend to accumulate in certain areas known as “hot-spots” (Figure 1), thus staying undetected. Number two, masked mycotoxins are not detectable with conventional methods due to physiochemical modifications that occur within the plant as a defense mechanism. These modifications yield a new compound, different from the original standard, impairing the ability of the analytical method to detect it. Although analysis results will show no (or low) contamination, in reality, there is a high risk of contamination as masked mycotoxins may be reconverted to toxic metabolites in the gastrointestinal tract of the animal.

Proper sampling and sample preparation are the foundations of quality mycotoxin testing. The main problem of assessing the presence of mycotoxins in feed and raw materials is their uneven distribution in the commodity, especially in whole kernels. Sampling is usually the largest source of error in the mycotoxin analysis and can result in up to 76% of the total uncertainty.

A so-called aggregate sample should be an accumulation of several small incremental samples taken from many different locations throughout the lot (Figure 2).
 

To gain insight into how to sample properly, we describe some possible scenarios below.

When taking samples during transfer, collect incremental samples of products (100 g) at periodic intervals while the product is transferred from one place to another (Figure 3).

When transferring with a loading bucket, collect samples of grain from each bucket being loaded (Figure 4).

For collecting incremental samples from a grain heap, take samples from across the entire surface area so that all parts of the lot have an equal chance of selection (Figure 5).

For roughages, the most practical way to take a sample is by hand. If possible, collect samples while the material is in motion. It is also important that all layers are represented equally. For sampling after ensiling, the fermentation should be completed beforehand. 

In the case of fresh roughages, leaves and stems are usually distributed at the edges of the truck. Therefore, take the incremental samples by hand, while the truck is being unloaded.

For bag and bunker silos, collect the incremental samples by puncturing the plastic cover using a sharp cone-shaped sampling device. Evenly distribute holes across the entire surface of the silo (Figure 6). Carefully refill each hole immediately after taking the sample and cover them using a strong tape to prevent possible contamination.
 

Due to variations in the distribution of leaves, stems and other materials in silage/straw bales, it is recommended to sample 20 small rectangular bales or 15 large bales. Combine 15-20 incremental samples from each bale to form an aggregate sample (Figure 7).