Mycotoxin Binders for Horses: Understanding Mold, Toxins & Feed Safety

Feed safety and management is one of the most critical factors in maintaining equine health and performance. Unfortunately, hidden threats like mycotoxins can sometimes invisibly contaminate hay and grains. Even with the best management practices, it’s nearly impossible to avoid mycotoxins altogether. That’s why many horse owners and nutritionists know the importance of including a mycotoxin binder in their horses' feed as an added safeguard.

This article explores what mycotoxins are, the molds that produce them, the health risks they cause in horses, and how binders can play a role in a complete equine nutrition program.

What Are Mycotoxins?

Mycotoxins are toxic compounds produced by molds and fungi. These organisms thrive in warm, humid, or damp conditions, making grains, pastures, and hay particularly vulnerable both before harvest and during storage.

Even with careful management, it’s impossible to eliminate mycotoxins from feed completely. Weather and storage conditions play a significant role in mold growth, meaning hay and grain harvested or stored during hot, humid, or drought-stressed seasons are at higher risk of contamination. Horses will inevitably consume small amounts, but the key is keeping levels within the FDA’s Center for Veterinary Medicine (CVM) safety standards. This is accomplished through ingredient testing, proper storage, balanced feed formulations, and the use of binders.

Scientists have identified more than 400 different mycotoxins, but only a few pose significant risks to horses. In the United States, the FDA/CVM monitors these five key toxins in feed:

  • Aflatoxins
  • Fumonisins
  • Deoxynivalenol (DON or vomitoxin)
  • Ochratoxin A
  • Zearalenone

 In addition to the toxins themselves, it is essential to understand the molds most likely to contaminate feed and forage and their role in producing mycotoxins. These fungi also thrive in warm, humid, or drought-stressed environments, particularly when hay or grain is poorly cured or stored.

The most common mold species that often contaminate hay include:

  • Alternaria – Frequently found in hay and grasses, and often a sign of poor forage quality.
  • Aspergillus – Common in stored grains and hay.
  • Cladosporium – Grows on damp forage and fermented, high-moisture forage.
  • Fusarium – One of the most significant mold groups in equine feeds, often present in cereal grains.
  • Mucor – Found in poorly dried or stored hay and silage.
  • Penicillium – Often grows in stored grains and hay.
  • Rhizopus – Common in spoiled hay and fermented, high-moisture forage.

How to Identify Moldy Hay

Hay can become moldy in just a few hours when heat and moisture are present. Dampness, musty odor, and visible mold growth are clear warning signs, and should never be fed to horses.

Moldy hay not only lowers the hay’s nutritional value but also produces spores and mycotoxins that can harm your horse. Laboratory testing can confirm the presence of mycotoxins in forage, especially if you suspect a large batch of hay is contaminated.

How Mycotoxins Affect Horses

Mycotoxin exposure in horses often produces vague, non-specific symptoms that can resemble other health conditions. Diagnosing mycotoxicosis in horses requires a veterinarian to piece together the horse’s history, clinical signs, diagnostic tests, and the elimination of other possible causes.

As such, horse owners should be alert for early warning signs of mycotoxin poisoning. Common clinical signs of mycotoxin intoxication include:

  • Reduced feed intake or refusing feed
  • Diarrhea and other intestinal irritation
  • Lethargy and poor performance
  • Respiratory issues such as coughing, heaves, or airway obstruction
  • Colic
  • Neurological symptoms (such as incoordination or paralysis in severe cases)

While some toxins, like DON, cause horses to refuse to eat contaminated feed naturally, others can produce severe or fatal outcomes if ingested and not identified quickly. Because of this, routine testing, good feed storage practices, and preventive strategies such as feeds including a mycotoxin binder for horses are essential. If mycotoxin poisoning is suspected, removing contaminated forage or grain from the horse's reach is critical to preventing more serious or fatal complications.

Even when mycotoxins are present at sub-lethal levels, chronic exposure can compromise horse health by:

  • Suppressing immunity
  • Reducing growth and performance
  • Impairing reproductive function
  • Increasing susceptibility to colic and other illnesses

The Top Five Most Concerning Mycotoxins for Horses

Although more than 400 mycotoxins have been identified, only five are considered significant risks to equine health. Of these, aflatoxins, fumonisins, and DON present the greatest concern. The five primary mycotoxins of concern are:

  • Fumonisins (Fusarium) – The most dangerous for horses, it disrupts sphingolipid synthesis, leading to equine leukoencephalomalacia (“moldy corn poisoning”). This neurological disorder is marked by poor coordination, head pressing, circling, and sometimes liver damage. Feeds with >10 ppm fumonisin B1 should never be fed to horses.
  • Deoxynivalenol (DON) (Fusarium) – A trichothecene that reduces feed intake. When combined with other mycotoxins, it can worsen health outcomes. Cold, wet harvest conditions increase the risk of DON.
  • Zearalenone (ZEN) (Fusarium) – Mimics estrogen and disrupts reproduction in horses. In mares, high levels can cause abortions or structural changes to the uterus and vulva. In stallions, it can cause genital flaccidity. Contamination is most likely in humid, cool weather.
  • Aflatoxins (Aspergillus) – More common in drought- or insect-stressed grains such as corn and oats. Aflatoxin B1 is the most toxic form, with safe limits set at 0.02 ppm by the FDA. Chronic exposure causes liver damage, poor appetite, depression, fever, and tremors. Levels above 2 ppm are typically fatal. Inhaled aflatoxins may also contribute to chronic respiratory disease.
  • Ochratoxin A (Aspergillus, Penicillium) – Can damage kidneys and suppresses immunity, though equine-specific data on this toxin is limited.

Understanding the Importance of Mycotoxin Binders for Horses

Mycotoxin binders are added to the horse’s diet to trap and remove toxins in the gastrointestinal tract before they enter the bloodstream. Research suggests these products can help reduce the harmful effects of mycotoxin exposure.

Studies also show that horses receiving mycotoxin binders often have lower toxin levels in the gut and display fewer clinical signs of poisoning. While not a cure-all, they can provide valuable protection when incorporated into a well-rounded equine nutrition program and feed safety program.

However, mycotoxin binders should never replace good feed management. Moldy hay or grain should not be fed under any circumstances, as binders cannot thoroughly neutralize its potentially dangerous side effects. Instead, they are most effective as a safeguard against accidental or low-level mycotoxin exposure that may occur even in carefully stored, high-quality feed and forage.

A variety of mycotoxin binders are available, each with different modes of action:

  • Yeast Cell Wall Extract: Derived from Saccharomyces cerevisiae, yeast cell walls have a strong ability to bind toxins. In addition to toxin binding, yeast supplements can support gut health, nutrient absorption, and immune defenses.
  • Bentonite Clay (Montmorillonite): A natural aluminum phyllosilicate clay that binds toxins and heavy metals in the gut. While effective at adsorption, it may also reduce the absorption of essential nutrients. Because of this, it is not typically recommended for long-term use without veterinary guidance.
  • Comprehensive Mycotoxin Binders and Digestive Feed Add-Ins: Some feed formulations pair a mycotoxin binder with additional ingredients such as prebiotics, probiotics, digestive enzymes, and phospholipids to enhance the horse’s ability to break down and absorb nutrients. These multi-functional feeds are designed to support overall gut health while reducing the harmful effects of mycotoxin exposure.

Discover Tribute Equine's Horse Feed with Mycotoxin Binders: Our Approach to Feed Safety and Mycotoxins

To protect horse health, Tribute® Equine Nutrition carefully monitors every ingredient for mycotoxin risk. Additionally, ingredients with significant risk are not utilized in Tribute formulas.

Distillers dried grains with solubles (DDGS) are a common feed ingredient produced during corn distillation for ethanol or alcohol. DDGS are rich in protein, fat, and phosphorus, and relatively low in sugar and starch. Unfortunately, the distillation process concentrates mycotoxins, leaving DDGS with higher levels than the original corn. For this reason, DDGS are not included in any of the Tribute® Superior Equine Nutrition line of feeds.

For added protection, all Tribute® feeds are formulated with a mycotoxin binder to help reduce the impact of these harmful compounds. Since forage is also a significant source of mycotoxins in the equine diet, the mycotoxin binders in Tribute® feeds also provide an extra safeguard.

FAQ: Mycotoxin Binders for Horses

  • What are mycotoxins, and where do they come from?

Mycotoxins are harmful compounds produced by molds and fungi such as Fusarium, Aspergillus, and Penicillium. These organisms thrive in warm, humid conditions and are commonly found in hay, grains, pastures, and even bedding.

  • How can I tell if my horse’s hay or feed is moldy or contaminated?

Warning signs include musty odors, visible mold growth, or excessive moisture. Mold can develop quickly under heat and humidity, and laboratory testing can confirm the presence of mycotoxins if contamination is suspected.

  • What are the symptoms of mycotoxin exposure in horses?

Clinical signs may include feed refusal, weight loss, colic, diarrhea, lethargy, respiratory issues such as coughing or heaves, neurological problems, and suppressed immunity.

  • Which mycotoxins are most dangerous to horses?

The five mycotoxins of most significant concern are aflatoxins, fumonisins, deoxynivalenol (DON or vomitoxin), ochratoxin A, and zearalenone. Fumonisins are particularly dangerous, as they can cause equine leukoencephalomalacia—also known as “moldy corn poisoning”—a neurological condition that is often fatal.

  • How can mycotoxin binders help protect my horse?

Mycotoxin binders, including clay minerals, yeast cell wall extracts, and organic polymers, work by trapping toxins in the gut before they enter the bloodstream. While not a replacement for safe feed practices, they can significantly reduce the negative impact of accidental or low-level exposure.

  • Are horses at greater risk during certain seasons or weather conditions?

Yes. Mycotoxin risk increases during hot, humid, or wet weather when mold thrives. Proper harvesting, drying, and storage practices are essential to minimize contamination and protect horse health.
 
 
References:

Article By:
Nicole Rambo, Ph.D.
Back to news