Mycotoxins are a hidden threat that can quietly chip away at herd health, milk production and overall performance. Produced by molds that grow on feedstuffs, these toxic compounds are more common than many farmers realize, and managing them requires a combination of prevention, monitoring and nutrition-based strategies.
According to Duarte Diaz, professor and dairy Extension specialist at the University of Arizona, the key is not to panic, but to recognize that mycotoxins are one of many risks that need to be built into routine feed and herd management.
Why Mycotoxins Are So Complicated
“When we say mycotoxins, we’re really talking about hundreds of different compounds, produced by many types of molds,” Diaz explains. “Each one behaves differently depending on the crop, the region, the weather and how feed is handled and stored.”
For example, Aspergillus molds, which produce aflatoxin, are more common in hot, humid regions, while Fusarium molds, which produce toxins like DON (vomitoxin) and zearalenone, are more likely in cooler climates. But Diaz points out that mold problems don’t follow hard rules.
“Even in drier or colder areas, the environment inside a grain bin or silage bunker can still create conditions that support mold growth,” he says. “That’s why we find mycotoxins in just about every major crop-growing region in the world.”
Feeds Most at Risk
Corn silage often gets the most attention, but other feeds can also carry risk. Diaz encourages producers to think about two factors:
- How often an ingredient is fed
- How attractive it is to molds
“Corn is widely grown and makes a good substrate for mold, so it’s always a top concern,” he says. “But cottonseed, peanut byproducts and even some small grains can also be high-risk depending on where and how they’re produced.”
He also emphasizes that details matter. For example, corn ears that are partially exposed due to poor husk coverage are more likely to get infected. Insect damage, drought or high heat during the growing season can also increase the chance of mold growth and toxin production.
Understanding What Triggers a Mycotoxin Outbreak
While molds and fungal spores are present in nearly every farm environment, they do not always produce toxins. So, what turns a common fungus into a toxic threat?
“It is similar to how we set our thermostats,” says Lina Castano-Duque, a mycotoxin researcher with the USDA Agricultural Research Service. “Fungi thrive in very specific environmental conditions. When the temperature, moisture and nutrient availability are just right, they grow rapidly and can start producing toxins.”
For example, Aspergillus grows best around 86°F.
“At that temperature, it grows quickly, produces more toxins and can spread across the field or storage site,” Castano-Duque explains.
Even more challenging is the fact toxin production is not always linked to visible mold or even active fungal growth.
“Sometimes the fungus grows without producing much toxin,” she says. “It often starts producing aflatoxin when it is stressed, which could be due to competition, nutrient shifts or environmental changes. We are still working to understand what exactly triggers that switch.”
Insect pressure plays a major role as well. Caterpillar damage, for example, can create small injuries in the crop that allow fungi to access starches and lipids inside the plant.
“If you have that kind of damage followed by warm and humid weather, the environment becomes perfect for the fungus to colonize and produce high levels of aflatoxin,” Castano-Duque says.
Testing and Monitoring
Identifying a mycotoxin problem isn’t always easy. Many symptoms, such as drops in production, weak immune response or poor reproduction can be caused by other factors. Diaz says testing should be part of a broader herd health and performance evaluation.
“Mycotoxins don’t usually cause one obvious sign,” he explains. “You’re more likely to see subtle issues over time, and they can be made worse by other problems like nutrition gaps or vaccine failures.”
Routine testing of high-risk ingredients and total mixed rations (TMR) can help spot a problem before it gets worse. And while moldy feed is often a red flag, visual cues alone are not enough.
“The most common call I get is, ‘My feed looks moldy but the test came back clean,’” Diaz says. “That actually makes sense. Mycotoxins are usually produced when the mold is stressed, not when it’s growing actively. So, a feed might look bad but be safe or look fine and still contain toxins.”
Can We Predict When Risk Will Be High?
To help producers stay ahead of contamination, Castano-Duque and her colleagues are developing predictive models that use environmental and soil data to estimate the likelihood of a mycotoxin outbreak.
Working with the National Corn Growers Association and other partners, USDA researchers are applying machine learning to evaluate variables such as temperature, precipitation, soil composition and historical outbreaks.
“Our goal is to generate a risk estimate about three months before harvest,” she says. “That way, a farmer in a specific county might get a notice that their region has a high likelihood of an outbreak, and they can take proactive steps.”
Interestingly, the models have revealed the influence of unexpected variables.
“In our Texas model, calcium carbonate in the soil turned out to be a highly influential factor,” Castano-Duque says. “That is important because calcium carbonate is often applied to adjust soil pH. Farms with more acidic soils tend to see higher risk, which lines up with what producers have observed for years.”
The models are still evolving, but the ultimate goal is to give producers tools to make more informed decisions, whether that means applying antifungal agents, adjusting crop management or watching feed quality more closely in a high-risk year.
What You Can Do
If mycotoxins are confirmed or strongly suspected, there are tools available to help reduce their impact. Feed additives, often called binders or sequestering agents, can help reduce how much toxin is absorbed in the cow’s gut. Diaz says some products can significantly lower the amount of aflatoxin that ends up in milk.
“For aflatoxin, a good product can cut levels by 50% to 60%,” he says. “That’s the difference between a marketable tank and a rejected load.”
He also recommends looking at overall ration quality and adjusting key areas to support the cow’s ability to cope. Mycotoxins often affect the immune system, liver and gut lining, so additional antioxidants, fiber sources and gut health additives can be useful.
“Think about what the toxin is damaging,” Diaz says. “Can we help the immune system recover? Can we support liver function? Can we reduce irritation in the gut? All of those things add up.”
Final Thoughts
There is no silver bullet for preventing mycotoxins, but building them into your farm’s risk management approach can help you stay ahead. Understanding which ingredients are most at risk, testing periodically and working with your nutritionist to make ration adjustments are all important steps.
“Mycotoxins are a part of modern dairy production,” Diaz says. “But they don’t have to take you by surprise. If you plan for them like you plan for heat stress or forage quality, you can minimize the damage and keep your cows on track.”
