By Carlos Campabadal, Ph.D., Extension Specialist, Department of Grain Science and Industry
During the fall crop harvest season, one of the most common concerns of farmers, elevator personnel, and end-users is high concentrations of mycotoxins and more specifically, aflatoxin in corn. Depending on who addresses this issue, it is not uncommon to hear different ways on how to measure and handle mycotoxins. However, the reality is that mycotoxins are commonly present on the grain where their concentrations vary widely and, in some cases, exceed thresholds of concern for human consumption and animal feed.
Presence of mycotoxins depends on several factors that can affect the plant and kernels during the growing season. These factors include drought, pest infestations, and extreme wet conditions, that cause stress to the plant allowing different types of molds to enter. If the ambient conditions and moisture content are ideal, mycotoxins can be produced. Despite the fact that scientists can predict the growth of molds and its production of mycotoxins, the only way to know if they are present is by sampling the grain.
The goal of sampling grain or any type of feed ingredient is to collect a portion from a larger quantity that represents the overall average condition. The larger quantity is referred to as a “lot” which can be anything where the grain is held. For example, it can be a truck load, a railcar, a silo, a bag, or any type of temporary storage. The science behind sampling is based on statistical procedures that use probability to determine the correct number of samples needed for each purpose.
There is scientific literature with detailed explanations on sampling that have served as fundamental information for different organizations or government institutions to develop their own sampling. For example, USDA’s Federal Grain Inspection Service (FGIS) has developed different sampling schemes for grain trucks, grain export vessels, etc. The nature of the sampling scheme is usually based on how consistent the quantity of the component to be measured is on a specific number of samples. This creates a statistical confidence that the number of samples from a lot will give us a true value of the average of the component’s quantity measured. For example, in a feed mill the number of samples to quantify protein content of soybean meal with a certain degree of confidence is less than the number of samples needed to quantify aflatoxin in corn in a similar sized lot. The protein content of soybean meal is usually fairly consistent in a given lot, whereas aflatoxin presence and levels are not.
The science will tell you to take several samples from a lot and mix them uniformly to get a composite sample. Also, it will tell you to take samples from at least 10% of the volume of the truck or railcar and that the higher the number of samples, the more precise your results. However, in day to day grain related operations including farms, there are many factors that can influence the way the sampling scheme is developed. These factors vary depending on each location’s conditions. For example, sampling during harvest when loads are coming in rapidly compared to other times when the pace is much slower. Other factors include availability of personnel and proper sampling equipment (grain probes both manual or automatic), precision or speed of analysis of the quality specs, and overall costs. The sampling of grain for quantifying mycotoxins in the field or during handling and storage is a difficult topic due to their nature and potential negative effects on animal health, market, etc. It is important to understand that in the field or in storage, mycotoxins are not uniformly distributed. On a farm, one field can have mycotoxins and the one next to it, might not. The same is true when grain is moved on trucks. It is common for one to five samples to be collected from grain trucks carrying feed ingredients or grain. More samples will always be better when trying to determine the true concentration of mycotoxins in a given lot.
Therefore, when analyzing reports or news articles about mycotoxin presence, it is important to pay attention to the number of samples and if they were taken at random locations. For example, there are reports that show aflatoxin presence on corn in the state of Kansas, but the number of samples for the analysis were only two. Therefore, would you trust this source considering the size of the state and the amount of corn grown?
In conclusion, the goal of this article is to create awareness that the better the sampling scheme, the more trust we can have on our results or interpretation of data and reports. It is important to know the reality of the quality of the crop that we grow or use.
