Mycotoxins in Feed

Mycotoxins in Feed

By Heather Smith Thomas

Mycotoxins are toxic fungal metabolites produced by molds such as Aspergillus, Fusarium, and Penicillium. They commonly develop in moldy, poorly stored, or drought-stressed feedstuffs, particularly corn, silage, and grains.

The presence of mold does not necessarily mean mycotoxins are present, but it does indicate that conditions are favorable for toxin production.

These fungal metabolites are small organic compounds produced during metabolism. When consumed by cattle, they can reduce feed intake, impair fertility, lower milk production, suppress immunity, and negatively affect overall health.

Preventing these losses depends on proper harvest practices, good storage management, and the use of products that help reduce the effects of mycotoxins.

Why Mycotoxins Are More Common Today

Mycotoxins have always been a concern in cattle production, but modern farming practices have increased their prevalence.

Stephanie Ward, Dairy Science Extension Specialist and Associate Professor at North Carolina State University, explains that fungi frequently grow on feed ingredients used in dairy rations.

Fusarium can infect crops before and after harvest, while Aspergillus and Penicillium are primarily post-harvest molds.

Even when mold is no longer visible, mycotoxins may still remain in the feed.

“Mycotoxins produced before harvest may remain stable during feed preservation, but molds can also grow during storage,” Ward says. Drought, excess moisture, heat, humidity, insect damage, and other stresses increase the risk of mold development.

Recognizing the Signs

Mycotoxicosis can affect cattle in many ways, including:

Increased incidence of squamous cell carcinoma (cancer eye).
Reduced appetite or feed refusal.
Lower milk production.
Poor reproductive performance.
Rough hair coat.
Lameness.
Diarrhea.

Symptoms vary depending on the animal’s age, stage of production, stress level, disease status, and the type, dose, and duration of mycotoxin exposure.

Because mycotoxins affect immune function and multiple organs, diagnosis can be difficult.

“Mycotoxins also affect livestock species differently,” Ward says. “For example, vomitoxin (DON) reduces feed intake in dairy cattle, while beef cattle and sheep appear more resistant.”

Understanding DON (Vomitoxin)

Deoxynivalenol (DON), commonly called vomitoxin, is produced by Fusarium molds and commonly contaminates wheat and corn during cool, wet conditions.

DON interferes with protein synthesis. In livestock it can cause feed refusal, poor weight gain, and vomiting.

“Often, the only treatment is removing the contaminated feed,” Ward says.

She also notes that naturally occurring mycotoxin contamination is often more severe than controlled research situations because multiple toxins are frequently present and may interact.

Although ruminants are generally more resistant than pigs, dairy cattle are especially vulnerable during early lactation when immune function is already suppressed.

Which Animals Are Most Susceptible?

Pigs and young poultry are among the most sensitive species, often experiencing severe growth losses, immune suppression, and reproductive failure.

Dogs, horses, and young calves are also highly susceptible.

Adult cattle are generally more resistant but can still experience significant production losses when exposed to high toxin levels or long-term contamination.

The Importance of Feed Testing

Mycotoxicosis can result from consuming either large amounts of contaminated feed or smaller amounts over an extended period.

Routine feed sampling and testing are important but challenging.

“Mold—and therefore mycotoxins—often occur in hot spots rather than being evenly distributed throughout a silo or grain bin,” Ward explains.

Because of this uneven distribution, negative laboratory results do not always guarantee feed is free of mycotoxins.

Ward recommends:

Taking core samples from multiple locations.
Avoiding single grab samples.
Freezing or drying samples before shipping to prevent additional mold growth.

“If feed tests negative but clinical symptoms remain, do not rule out mycotoxin contamination,” she says.

Managing Contaminated Feed

Several strategies may help reduce the effects of contaminated feed.

Traditional clay binders—including bentonite, zeolites, and hydrated sodium calcium aluminosilicate (HSCAS)—have been studied for years.

Research shows that some clays work well against certain toxins, but effectiveness varies.

For example:

HSCAS is effective against aflatoxin.
It has little effect on other mycotoxins.
Some toxins, including zearalenone and ergot alkaloids, do not bind to clay products.

When contamination occurs, removing contaminated feed is often the best solution. If toxin levels are below FDA action limits, dilution with clean feed may also be an option.

Why Modern Farming Increases Risk

Dr. Larry Roth, Vice President of Nutrition at Agrarian Solutions, says molds produce mycotoxins as a survival mechanism.

“They don’t care about livestock,” Roth explains. “They’re simply trying to keep competing organisms out of their territory.”

Plant stress—including drought, excess moisture, temperature extremes, and insect damage—makes crops more susceptible to mold growth.

Modern agronomic practices can further increase risk. Dense crop canopies retain moisture, reduce airflow, and block sunlight, creating ideal conditions for mold growth.

Conservation tillage also leaves crop residue on the soil surface, providing another source of fungal infection for emerging plants.

Poor silage packing, delayed covering, weather damage, and extended feed storage further increase opportunities for mold development.

By-products such as distillers grains and corn gluten feed can also concentrate mycotoxins.

Today’s Cattle Are More Vulnerable

Roth believes modern cattle are more susceptible because genetic selection has emphasized growth and production over resilience.

“Our animals are like finely tuned race cars,” he says. “Little things like mycotoxins can cause a wreck.”

Today’s cattle consume more corn silage, small-grain silages, and by-products than previous generations, increasing exposure to mycotoxins.

At the same time, pregnancy, lactation, transport, vaccination, harsh weather, and other stresses further weaken immune defenses.

Effects on Reproduction and Calves

When cows consume mycotoxins, nutrients are diverted away from production and toward detoxification and immune function.

This can reduce:

Fetal growth.
Colostrum quality and quantity.
Milk production.
Reproductive performance.

Because calves rely entirely on colostrum for antibodies, poorer-quality colostrum leaves them more vulnerable to disease.

Replacement heifers may also grow more slowly, respond less successfully to timed AI programs, and experience reduced fertility.

“The body’s first priority is survival, not reproduction,” Roth says.

Hidden Costs to Production

Roth describes mycotoxins as “silent profit robbers.”

Beyond reducing milk production and growth, they impair nutrient utilization throughout the animal.

As cows mobilize body fat after calving, stored mycotoxins are released into circulation. The liver must divert energy toward detoxification instead of producing nutrients needed for milk production and metabolism.

The result is reduced productivity throughout the herd.

New Approaches to Mycotoxin Control

Traditional clay binders primarily target aflatoxin and may also bind important nutrients, including amino acids and vitamins A and E.

Yeast cell wall products have similar limitations.

Agrarian Solutions has taken a different approach.

Rather than binding toxins, the company’s DTX product uses specialized probiotics to activate the animal’s natural intestinal defense mechanisms.

According to Roth, these beneficial bacteria stimulate proteins that help remove mycotoxins from intestinal cells before they are absorbed.

“These bacteria act like garbage trucks,” he says. “They trigger the animal’s natural defense system so it can better protect itself.”

Backed by more than 25 years of research, Roth says this approach helps cattle cope with today’s greater mycotoxin challenges while maintaining health and performance.

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