For 10 years our organization has been conducting a harvest analysis that surveys mycotoxin occurrence and levels. The data from corn silage and corn grains is utilized to identify areas of lower or higher risk due to weather patterns and to assess how the mycotoxins present may impact livestock production and health.
Weather stresses such as drought, excess rainfall, hail and wind are evaluated as to how they may have influenced the mycotoxins present. Drought creates an environment for aspergillus molds which produce mycotoxins such as aflatoxin B1. Rainfall, whether it is excessive or timely, can be the environment for fusarium molds that produce deoxynivalenol, zearalenone, fusaric acid and many of the emerging mycotoxins group.
Much of the Upper Midwest received at or near record rainfall that delayed planting or caused replant situations. Many anticipated increased risk for fusarium mycotoxins, but the rain stopped in late June, prior to the crop tasseling and pollinating. This is a critical time for the risk of mold infestation and growth. The eastern U.S. was under drought for a great period of the growing season. This stressed the crop, which was then exposed to increased rainfall prior to harvest. Fusarium mycotoxins such as deoxynivalenol, zearalenone, fusaric acid and fumonisins flourished.
Corn silage
The results for the 347 corn silage samples from across the U.S. showed an average of 8.3 mycotoxins per sample. The most often occurring mycotoxin groups were emerging mycotoxins, at 98.6%; type B trichothecenes, at 96.8%; fumonisins, at 91.6%, fusaric acid, at 91.4%; and zearalenone, at 36.9%. Ninety-nine percent of the samples contained two or more mycotoxins. Multiple mycotoxins can be a more significant risk due to additive and synergistic actions.
The mycotoxins with the highest average risk to dairy cows were the type B trichothecenes, with an average level of 1,864.9 parts per billion (ppb) and a maximum level of 43,717 ppb. Levels of 500 ppb to 1,000 ppb may begin to show impact on cow health and performance. A level at 2,000 ppb may begin to show significant impact on cow dry matter intake, milk production, the rumen microbiome, conception rates, embryo health, gut wall integrity, liver function and immune response. The level of type B trichothecenes remained at the average level throughout the harvest season.
Emerging mycotoxins, fumonisins, fusaric acid and zearalenone had lower average levels, but the maximums for all were at higher risk levels. The danger here is that if the same sample has two or more mycotoxins at near maximum levels, cow health and performance can be at a much greater risk.
Overall, 2024 corn silage had an average risk equivalent quantity (REQ) of 208.1, where high risk starts at 150. The REQ is a calculated estimate of the risk from all the mycotoxins present and not just the mycotoxin at the highest level. The trend was for corn silage from the western Corn Belt to be at a lower REQ risk and the eastern U.S. to be higher. The REQ impact, on average, for milk production loss was 1.1 pounds per cow per day, with a potential increase in somatic cell count of 69.09%.
Corn grains
Over 140 samples of corn grains had an average of 8.0 mycotoxins per sample, with 100% of the samples containing two or more mycotoxins. As in the corn silage samples, the most often occurring mycotoxin groups were fusarium products. Emerging mycotoxins were in 100% of the samples, while fumonisins were in 86.7%, type B trichothecenes 83.9%, fusaric acid 81.1% and zearalenone 50.3%. The greatest risk level on average was from type B trichothecenes, with an average of 727.0 ppb but a maximum of 17,622 ppb. Other mycotoxin groups with concerning maximum levels were emerging mycotoxins at 8,313 ppb, fumonisins at 57,129 ppb, fusaric acid at 1,931 ppb and zearalenone at 1,054 ppb. While the risk to the cow may be lower due to a lower inclusion rate compared to corn silage, these mycotoxins will still add to the risks from corn silage. The REQ from corn grains is 98.5, which is moderate, but there is a maximum of 1,602, which at a normal inclusion rate of corn grains in feed would be a higher risk to dairy cows.
A point to keep in mind for corn grains is that the harvest season was warmer and drier than normal across a major portion of the corn-growing region. This resulted in grain drying rapidly in the field. When it was harvested, there was somewhat greater kernel damage, and there were higher levels of foreign matter in the harvest. These issues can lead to an opportunity for greater mold growth in storage, which may lead to an increase in mycotoxin levels. Stored corn from the 2024 crop should be closely monitored.
Looking forward into winter and spring
As the 2024 corn silage and corn grains are used to manufacture total mixed rations (TMRs), the mycotoxin risks from the growing season and storage can be evaluated. The REQ for TMR samples submitted to our lab for analysis in January of 2025 was 160.3, where 150.0 is higher risk. The mycotoxin group with the greatest risk was type B trichothecenes (DON group), with an average of 1,361.5 ppb and a maximum of 6,406 ppb. Compare this data to the same month for the previous year, when the REQ showed a moderate risk of 120.4 with a maximum of 517. Type B trichothecenes at that time were at an average of 849.9 ppb and a maximum of 4,390 ppb.
Take-home
The weather had an impact on the corn crop for 2024. Corn silage has a risk from multiple mycotoxins, with type B trichothecenes being the greatest risk. Corn grains, like corn silage, have multiple mycotoxins, with the greatest risk from type B trichothecenes. Stored corn grains may be at greater risk due to damaged kernels and a higher percentage of foreign matter. Compared to the 2023 crop, the 2024 crop shows a higher REQ when manufacturing TMR for dairy cows.
