By Josep Garcia-Sirera (Toxins product manager)
Fungi, mold, and bacteria can develop anywhere: in the field, during storage, or in feed. Storage fungi—typically belonging to the Aspergillus and Penicillium genus—contaminate raw material or feed during storage, transport, or processing. In these stages, growth depends on moisture level, damage to the grains, entrance of water, temperature fluctuations, etc. Though there are many factors, basic preventative measures can be taken to reduce the risk of storage mycotoxins.
When it comes to mycotoxins, there are some factors that are uncontrollable, like the weather during planting, growing, and harvest. Post-harvest is where certain measures can be taken to reduce the chances of mold growth and the stressors that trigger the production of secondary metabolites, also known as mycotoxins. By understanding the favorable environments for fungi, measures can be taken to reduce growth opportunities during transportation and storage.
Prevent cross-contamination
The first step to reduce the risk of mycotoxin contamination is to limit exposure and avoid mixing clean grain with dirty grain. Though a low risk of mycotoxin transfer, it is good practice for trucks and containers to be completely emptied between loads. Ideally, they are swept too. Mixing occurs during loading and unloading. This can be a positive as it cools and distributes existing mycotoxins throughout the grain to reduce areas of concentration that can easily become ‘hot spots’. With this, proper handling of grains needs to be considered, as broken or damaged hauls expose the saccharides in the grain to molds and fungi.
Create a hostile environment
The second determinant is understanding what environmental factors contribute to fungal and mold growth to prevent the opportunities for mycotoxins. Of the 450+ known mycotoxins, most harmful mycotoxins originate from the Penicillium, Aspergillus, and Fusarium genera. Fusarium is considered a ‘field’ fungus, meaning it typically develops in the field, while Penicillium and Aspergillus are commonly referred to as ‘storage’ molds (Figure 1). Each toxin has its preferred environment and controlling the storage environment is the next step to reducing the risk of mycotoxins.
Common storage molds
Perhaps the most impactful way to mitigate the risk of molds, and the potential for mycotoxins, is to reduce the moisture content of the grain as soon as possible after harvest. Drying wheat and corn to 14% and 15% moisture respectively will limit spoilage and potential fungal growth. Following drying, allow the grain to cool. This can be a challenge based on the temperature at harvest but, similar to putting food in the refrigerator, mold activity is typically reduced in cooler environments. Once the grain is sufficiently dry and cool, a fungicide can be applied before the grain is placed into an empty, clean, and dry storage area free of holes. However, this fungicide will only eliminate existing molds/fungi, not mycotoxins. By applying a treatment, mold growth may be reduced, preserving the grain’s nutritional value—as molds consume valuable sugars—and decrease the risk of mycotoxin production by a stressed mold.
Still, the best practice is simply to dry the grain, have a clean storage area, and maintain a climate that is hostile to molds. This can be achieved by applying the all-in-all-out practice. All grain is removed from the bin and the container is inspected before being filled with new grain. Depending on the size of the operation, this can be a challenge. Even so, it is best to perform a visual inspection (ensuring no grain is stuck to the walls or left in the corners) before the grain is added from the next harvest. If all-in all-out cannot be achieved, empty the bin as much as possible before adding new grain. Follow safety standards when working in/around bins.
Maintaining the space
At the level of feed factories, especially in the silos, fungi mostly grow where humidity is prevalent. These points occur via the movement of moisture from the silo’s exterior, particularly at night when ambient temperatures drop (Figure 2). The changes in temperature produce condensation on the internal walls of the silo, which promotes the growth of fungi. The same phenomenon can occur in trucks, shipping containers, and other compartments where grain or feed is stored.
Changes in the storage environment can favor mold growth
To avoid this fluctuation and condensation build-up, temperature and humidity control needs to be considered. This can be achieved with ventilation to avoid heat and moisture. If contamination does occur, removal of tainted parts to prevent further spread is recommended. It is worth noting that molds do not equate to mycotoxins, as mycotoxins are formed when molds experience stress. The most common form of stress for a mold is anything that hinders its growth. This often occurs when the environment changes to a non-ideal climate, typically dry and cold, resulting in mycotoxin production. However, when they have a pleasant climate, molds consume sugars in the grain to decrease the grain’s nutritional value.
Pests—like rodents, birds, and flies—can be reduced by sweeping and discarding excess grain laying on the ground and ensuring grain is stored in a space with no holes. Regular cleaning of the area surrounding the bin and not allowing weeds to grow against the bin is imperative.
In summary, the lack of proper storage management encourages mold growth, resulting in a reduced quality of grain and lost grain. If stressed, this same mold, often Aspergillus and Penicillium, produces dangerous mycotoxins. Despite preventive measures, most feedstuffs are contaminated by at least one mycotoxin in the field and this number exponentially increases by the time it reaches the farm. This is shown in a study by North Carolina State University, which found that corn samples from the field were found to be 30% positive for mycotoxins. Followed to the feed mill, the same grain was 52% positive for mycotoxins and 91% positive by the time it arrived on the farm in the feeders. The increase of storage toxins results in an added risk to the animals that consume them. Although mycotoxin formation is strongly correlated with geographical regions, global trade causes cross-contamination of most mycotoxins all over the world. This is why, in addition to proper storage strategies, a scientifically proven toxin binder is important to protect animals against the adverse risks of mycotoxins.
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