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Don’t be fooled by these five mycotoxin myths

Neil Michael for Progressive Dairyman Published on 31 May 2019

Mycotoxin contamination, caused by molds and fungi that appear in feed, is an urgent concern in dairy rations across the country this year. A recent mycotoxin report warns that contamination levels in the 2018 crop present a medium-to-high risk to livestock.

Without proper management, mycotoxins may reduce feed consumption, alter reproductive performance, reduce nutrient utilization, irritate tissues – especially in the gastrointestinal (GI) tract – and cause cellular death. 



Despite the high prevalence and well-known dangers of mycotoxins in dairy herds, several misconceptions persist that prevent producers from managing mycotoxins effectively. Don’t be fooled by these five mycotoxin myths:

Myth: Mycotoxins are only a problem in wet years

Truth: During the growing season, temperature and humidity fluctuations often lead to growth of different types of molds. Some molds prefer cool, wet environments and others like hot and humid conditions. Under stressful conditions due to weather extremes, insect damage or poor storage, molds produce toxic secondary metabolites known as mycotoxins. Thus, mycotoxins always need to be on your radar regardless of environment, growing year or location.

The fact is, mycotoxin contamination may be even more common than you realize. For example, in tests of the 2018 U.S. corn crop across 31 states, 98% of ground corn samples and 90% of corn silage samples tested positive for at least one mycotoxin.

Myth: If mycotoxin tests are negative, there’s no need to worry

Truth: Feed analyses might not reveal the whole picture because not all mycotoxin species show up in testing. Analyses also may be hindered because of inconsistent mold growth and mycotoxins not being uniformly distributed within a feedstuff. Often, it is difficult to obtain representative samples for accurate testing. In fact, sampling error accounts for 90% of inaccuracies in mycotoxin analyses.

More importantly, research shows multiple mycotoxins at “nonsignificant” or undetectable lab levels can have a cumulative effect, creating chronic, negative impacts on the animal. The ingestion of low-level toxins may cause an array of metabolic, physiologic and immunologic disturbances.


That’s why it can be difficult to pinpoint which mycotoxins are the root cause of a dairy’s health challenge or where contamination occurred. Considering the potentially severe impact of mycotoxins, dairy producers should approach mycotoxins the same way they handle subclinical milk fever and ketosis: Assume mycotoxins are present and proactively manage the herd to reduce their negative effects.

Myth: The rumen detoxifies mycotoxins

Truth: Ruminants do have some ability to detoxify consumed mycotoxins, but the process has a negative impact on rumen bacteria populations. During detoxification, it is possible for the bacteria to create even more toxic byproducts, known as conjugated mycotoxins. These altered mycotoxins can impact normal function in both the rumen and intestines. 

Also, due to a faster rate of passage in high-intake, high-producing animals, many consumed mycotoxins can escape the rumen before being detoxified and damage the lower intestines.

Even if the rumen bacteria successfully detoxify mycotoxins, the presence of mold in feed may increase refusal rates, reducing nutrient utilization and performance in a herd. Mycotoxins have been associated with various factors that reduce performance, including irregular estrous cycles, embryonic mortalities, pregnant cows showing estrus and decreased conception rates.

Myth: Dilution is the solution to mycotoxins

Truth: A common strategy to manage mycotoxins on many farms is to mix contaminated feeds with good-quality feedstuffs and hope that dilution is enough to mitigate the harmful effects. However, because the rumen isn’t always successful in detoxifying mycotoxins, even one bite of contaminated feed can significantly impact the intestines.

The single layer of intestinal lining cells and associated immune cells is the primary target for ingested mycotoxins. Once exposed, inflammatory compounds are released, causing local damage to the intestine’s lining. These toxins compromise the GI tract and can decrease the surface area available for nutrient absorption. This opens the door to growth of pathogens like salmonella, clostridia and E. coli. Inflammatory cytokines released into the bloodstream can cause inflammation to liver, lungs and other organs.


Although not all mycotoxin challenges result in clinical disease, any mycotoxin exposure reduces performance as a result of the additional energy required to manage the immune response and repair the gut integrity. The moral of the story is to protect the gut every day, with every bite – not just when clinical cases occur.

Myth: Feeding clay solves mycotoxin problems

Truth: Clay and other binders can successfully bind some types of mycotoxins, but not others. Hundreds of different mycotoxin species exist, so traditional binders may leave the animal vulnerable.

Tests of the 2018 crop show that co-contamination with multiple species is on the rise. More than 60% of 2018 corn silage samples contained more than one mycotoxin species compared with only 30% in 2017. In corn, 72% had more than one mycotoxin versus 47% in 2017.

In addition to their effectiveness being limited to certain mycotoxins, binders do not protect the gut from their harmful effects.

A more advanced alternative is feeding refined functional carbohydrates (RFCs), which are natural carbohydrates that are biologically active in the gut to reduce pathogen impacts and prepare the immune system ahead of environmental challenges so animals can respond quickly. Regardless of the specific mycotoxin involved, RFCs protect the gut and prevent mycotoxins from being absorbed and entering the blood circulation. The toxins then pass harmlessly through the digestive system and are excreted without negatively affecting animal performance.

Research shows that immune suppression caused by mycotoxins can be reversed by beta 1,3/1,6 glucans and mannans present in RFCs, allowing the cow to further protect itself against pathogens. In addition, nutrient uptake is maintained, leading to better feed efficiency and animal performance. 

This level of protection enables animals to devote energy to all functions instead of staving off infections or struggling to maintain nutrient uptake in the face of mycotoxin contamination. RFCs can help dairy producers manage unseen threats from mycotoxins and other pathogens, building a resilient immune system that protects animals from the ill effects of these challenges.

Know mycotoxin truths

Don’t fall victim to complacency about mycotoxins. Understanding and addressing the dangers of mycotoxins can keep them from robbing your cows of immunity, feed efficiency and performance.  end mark

Neil Michael received both DVM and MBA degrees from Purdue University and has over 30 years of industry experience including veterinary practice, dairy management, reproduction and nutritional consulting.

References omitted but are available upon request. Click here to email an editor.  

Neil Michael
  • Neil Michael

  • Manager, Ruminant Technical Services
  • Arm & Hammer Animal and Food Production
  • Email Neil Michael