The Importance of Understanding Mycotoxins

Mycotoxins have become an increasingly important topic in equine nutrition, with new research confirming that most forages, pasture, and compound feeds can contain multiple mycotoxins. These toxins are produced by fungi and moulds in pasture, hay, haylage, cereals, and bedding and have the potential to significantly affect your horse’s health, behaviour, and performance.

In our latest article, we discuss what mycotoxins are, how they affect your horse and how you can help reduce their impact for optimum health and well-being:

What are Mycotoxins?

Mycotoxins are produced by moulds and fungi such as Fusarium, Aspergillus, and Penicillium. They are toxic secondary metabolites which means they are chemical compounds produced by fungi/moulds that are not essential for growth but give the fungi/moulds an advantage as defence or survival tools and, when consumed in high levels, can be harmful to horses.

More than 500 different mycotoxins have been identified, and horses can often be exposed to multiple mycotoxins at once, which can amplify their effects.

Fungi and mould spores thrive in warm, humid, oxygen‑rich environments conditions increasingly common in the UK due to changing weather patterns, particularly in spring and summer. Mycotoxins are heat‑stable, which means that they can survive processes such as pelleting and digestion.

Forage can be contaminated at two key stages: In the field (pre‑harvest) and during storage (post-harvest)

In the field: Field fungi such as Fusarium affect grasses and cereal crops during growth. Humid, warm, or fluctuating weather conditions encourage their development. A 2025 European grassland study found mycotoxins in nearly all pasture samples, regardless of rainfall or temperature, highlighting how widespread contamination can be [1].

During storage: Storage fungi such as Aspergillus and Penicillium can thrive when hay or haylage is baled too wet, when plastic wrap is punctured, or when feed is stored in warm, damp, or poorly ventilated conditions. These fungi can continue producing toxins long after the forage has been harvested.

Because horses consume large quantities of forage daily and have a sensitive digestive system, they can be particularly vulnerable to the effects of these toxins when consumed in large quantities.

Types of Mycotoxins

There are three main groups of fungi responsible for producing the mycotoxins that affect horses: Fusarium, Aspergillus, and Penicillium. Each behaves slightly differently, and understanding where they come from helps explain how horses are exposed to them.

Fusarium species are typically found out in the field, growing on grasses and cereal crops before they are ever harvested. This means that many mycotoxins are already present in pasture, hay, and haylage long before they reach the yard. Fusarium produces several well‑known toxins, including the trichothecenes (such as deoxynivalenol, or DON), which interfere with normal cell function and can irritate the gut lining, reduce appetite, and weaken the immune system. Another important group of Fusarium toxins is the fumonisins, to which horses are particularly sensitive. These toxins are associated with serious neurological and liver damage, including equine leukoencephalomalacia (ELEM), a condition linked to mouldy maize but now recognised more broadly in contaminated forage. A 2025 UK study found fumonisins and other Fusarium toxins in forage fed to horses with unexplained liver disease, strengthening the link between forage mycotoxins and equine hepatic injury [2].

In contrast, Aspergillus and Penicillium tend to appear after harvest, thriving in stored forage and feed.

A separate but increasingly important category involves endophyte‑related toxins found within certain grass species themselves. Ryegrass and tall fescue can harbour endophytic fungi that live inside the plant and produce compounds such as ergovaline and lolitrem B. These toxins don’t rely on visible mould; they are produced within the plant tissue and can affect horses grazing on otherwise healthy‑looking pasture. Endophyte toxins are known to cause vasoconstriction, poor thermoregulation, reproductive issues in mares, and neurological signs.

Together, these different fungal groups create a complex picture. Horses are rarely exposed to just one toxin at a time. Research has shown that co‑contamination is the norm, not the exception. This overlapping exposure is one reason mycotoxin‑related symptoms can be so varied and difficult to pinpoint.

Signs of Mycotoxin Exposure

Horses can be exposed to multiple toxins which means that symptoms can be difficult to pinpoint and are often and varied, they can include:

• Unexplained poor performance
• Reduced appetite
• Behavioural changes
• Compromised immunity
• Neurological signs
• Liver enzyme elevations
• Diarrhoea or inconsistent manure
• Photosensitivity
• Swollen mammary glands or altered seasons in mares

Diagnosis can be costly and typically involves ruling out many other potential causes of the symptoms and also testing forage through a reputable laboratory.

Prevention and Management

Although it impossible to eliminate mycotoxins entirely, there are ways that horse owners can reduce their impact.

Good pasture and forage management is the first line of defence. Avoiding overgrazed or drought stressed fields can help limit the conditions in which endophytes and field fungi thrive, while allowing grass to grow with adequate leaf cover reduces plant stress and the likelihood of toxin production.

Once forage is harvested, storage becomes critical. Hay benefits from being stored for at least three months before feeding, giving naturally occurring mould organisms time to die off. Haylage, on the other hand, must remain tightly sealed; even a small puncture in the wrap can allow air to enter and encourage mould growth. Any bale that smells musty, feels warm, or shows visible spoilage should be avoided.

Feed hygiene also plays an important role. Buying from reputable suppliers who follow recognised quality assurance schemes, such as FEMAS, helps ensure that cereals and compound feeds have been produced and stored under controlled conditions. Once on the yard, feed should be kept in clean, dry, sealed containers and used within a reasonable timeframe to prevent moisture build‑up or contamination.

The same principles apply to bedding. Straw, in particular, can harbour moulds, and horses may ingest it. Ensuring bedding is clean, dry, and well‑stored reduces this risk, especially for horses on restricted grazing who may be more inclined to nibble their beds.

Forage testing can be a useful tool when mycotoxin exposure is suspected, although results should always be interpreted alongside clinical signs and with appropriate veterinary guidance. Because mycotoxins are so widespread, testing is often most valuable when used to rule in or rule out specific concerns, or when comparing different batches of forage.

Ultimately, prevention relies on a combination of good pasture management, careful forage selection, and appropriate storage practices, all of which help minimise the overall toxin burden your horse is exposed to.

What about Toxin Binders?

The use of toxin binders can be an increasingly important strategy in managing mycotoxin exposure in horses, largely because completely avoiding these compounds is almost impossible. Even good quality forage can contain a mixture of low level mycotoxins, and while each toxin alone may not cause obvious harm, their combined effects can place strain on the digestive and immune systems. This is where toxin binders have a part to play as a practical tool to help reduce the overall burden and impact on the horse.

Toxin binders work by attaching to mycotoxins in the gut before they can be absorbed into the bloodstream. Once bound, the toxins are carried safely through the digestive tract and excreted. However, not all binders work in the same way, and their effectiveness depends heavily on the type of mycotoxin involved.

Inorganic binders, such as bentonite clays and aluminosilicates, have been widely studied and are known to be particularly effective at binding aflatoxins. These toxins are more commonly associated with contaminated grains, and clays have a strong affinity for their chemical structure. Research across species, including work by Fink‑Gremmels (2008) [3] and Döll & Dänicke (2011) [4] consistently show that while clays are excellent for aflatoxins, they are far less effective at binding the fusarium derived toxins most relevant to horses. This limitation is one of the reasons clay‑based binders are not considered the most reliable option for equine diets.

Organic binders, particularly those derived from yeast and algae cell walls, offer a broader and more versatile binding capacity. Yeast cell wall components such as β‑glucans and mannans have been shown to interact with a wide range of mycotoxins. A study Gallo & Masoero (2010) [5] demonstrate that yeast‑based binders can effectively bind toxins like zearalenone and ochratoxin A, making them more suitable for the diverse mycotoxin profiles found in forage.

Algae‑derived components appear to enhance this effect even further. Although not equine focussed, research by Yadavalli, R et al (2023) [6] highlights the ability of algae cell wall polysaccharides to bind mycotoxins, expanding the range of compounds that can be neutralised before absorption. This is particularly valuable given the increasing complexity of mycotoxin contamination patterns in modern forage.

Beyond their binding ability, organic binders offer another important advantage: they support the health of the hindgut microbiome. Mannan oligosaccharides (MOS), for example, can bind to pathogenic bacteria, helping to reduce their numbers and create a more favourable environment for beneficial microbes. This has been demonstrated in equine‑specific research, including work by Garcia Diaz et al. (2018) [7]. Because mycotoxins can disrupt microbial balance, reduce fibre digestion, and impair immunity, the ability of MOS to stabilise the hindgut adds an important secondary layer of protection.

Recent research has also emphasised the importance of using binders capable of addressing multiple toxins at once, since co‑contamination is now recognised as the norm rather than the exception. A study by Monbaliu et al. (2010) [8] demonstrated widespread multi‑mycotoxin contamination in feed ingredients, reinforcing the need for broad‑spectrum solutions. For this reason, products that combine yeast, algae, and other functional ingredients are gaining traction, offering a more comprehensive approach to managing the complex and ever‑changing mycotoxin landscape.

In short, toxin binders are not a replacement for good forage management, but they are a valuable tool in reducing the risks associated with unavoidable mycotoxin exposure. The most effective options for horses tend to be those based on organic materials, particularly yeast and algae, which provide both broad‑spectrum binding and additional digestive support.

How ReMove can help protect your horse

With how widespread mycotoxins are and how varied their effects can be it is easy for horse owners to be overwhelmed when the best quality forage can contain a mixture of low‑level toxins with horses are often exposed to several at once.

This is where a well‑designed toxin binder can become a valuable part of a horse’s nutritional routine, helping to reduce the overall burden on the digestive system and support long‑term health.

ReMove has been formulated with an understanding of mycotoxin challenges in mind. Rather than relying on a single ingredient or a narrow binding mechanism, it brings together a combination of yeast‑derived, algae‑derived, and functional oil components, each chosen because they address a different part of the problem highlighted in current research.

At the heart of ReMove is Mycosorb A+, a blend of yeast and algae cell wall fractions. As discussed earlier, yeast‑based binders have been shown to interact with a broad range of mycotoxins, including those produced by Fusarium, which are particularly relevant to horses. Studies have demonstrated that yeast β‑glucans and mannans can bind toxins such as zearalenone and ochratoxin A, reducing their absorption and helping to protect the gut lining. The inclusion of algae adds another layer of support, as algae‑derived polysaccharides have been shown to bind both polar and non‑polar toxins providing an important advantage given the complex contamination patterns now seen in forage.

ReMove also contains Actigen and Ecocell, two sources of mannan oligosaccharides (MOS). These compounds don’t just contribute to toxin binding; they also help stabilise the hindgut microbiome by binding pathogenic bacteria and supporting the growth of beneficial microbes. This is particularly important because mycotoxins can disrupt hindgut fermentation, reduce fibre digestion, and weaken immune function. By supporting microbial balance, MOS helps counteract some of the secondary effects of mycotoxin exposure, promoting a healthier digestive environment overall.

The final component is PowerStance, providing a source of coconut‑derived lauric acid. Lauric acid has natural antimicrobial properties, helping to reduce the presence of toxin‑producing microbes in the gut. It also supports digestive comfort and appetite, two areas that can be affected when horses are exposed to mycotoxins, even at low levels.

Together, these ingredients create a multi‑layered approach that reflects what the research tells us: that no single binder can address the full spectrum of mycotoxins horses encounter, and that supporting gut health is just as important as binding toxins themselves. ReMove doesn’t claim to eliminate mycotoxins, no product can do that, but it does offer a practical, scientifically aligned way to reduce their impact and support your horse’s digestive health, immune system and long term wellbeing.

If you have any questions about creating the best diet and nutrition for your horse or pony, please contact 01488 73322 or info@boomerangnutrition.co.uk.

References:

1. Selier, H. et al. (2025). Environmental conditions and plant diversity show little effect on mycotoxin occurrence in European grasslands used for horse husbandry.
2. Bates, A et al. (2022). Investigation of forage mycotoxin levels in horses with increased liver enzyme concentrations
3. Fink‑Gremmels, J. (2008). Mycotoxins in cattle feeds and carry‑over to dairy milk: A review.
4. Döll, S. & Dänicke, S. (2011). The Fusarium toxins deoxynivalenol (DON) and zearalenone (ZEN) in animal feeding.
5. Gallo, A. & Masoero, F. (2010) In vitro models to evaluate the capacity of different sequestering agents to adsorb aflatoxin
6. Yadavalli, R et al (2023) Biological detoxification of mycotoxins: Emphasizing the role of algae
7. Diaz, T.G. et al (2018) Inclusion of live yeast and mannan-oligosaccharides in high grain-based diets for sheep: Ruminal parameters, inflammatory response and rumen morphology
8. Monbaliu, S. et al. (2010). Occurrence of mycotoxins in feed as analyzed by a multi-mycotoxin LC-MS/MS method