Leading figures in the equine industry agree: The exposure of horses to mycotoxins is a critical area requiring attention. All horses come into contact with mycotoxins on a daily basis, and while they can never be completely eliminated, good feed and management practices can reduce mycotoxin exposure.




How do mycotoxins impact horses?

Mycotoxins are harmful byproducts of mold growth that are produced under certain conditions. They can occur in growing, harvested or stored grain and forage crops, and when exposed to horses through feed materials, grazing or bedding, mycotoxins can have a significant impact on the animal’s health.

Molds familiar to the equine industry include Rhizoctonia on clover, ergot toxins on ryegrass and grain, and Acremonium on fescue. These molds are challenging to eradicate; their growth rates tend to increase when the plant is under stress because of extreme weather conditions or heavy grazing. These mycotoxins are most prevalent in plants grazed on or harvested during a wet autumn, following a dry summer.

Until recently, there has been limited research about the effects of mycotoxins on horses, with data usually cited from the swine or ruminant industries.

Using non-equine data effectively is somewhat challenging. A horse may be comparable to a ruminant in the role of a forage grazing animal, but it has a gastrointestinal tract more closely related to the pig. The addition of the hindgut fermentation process adds another complication.

The requirements for a horse are also significantly different from those for livestock species. The focus for equines is less on growth and meat, and more on conformation, temperament, performance and durability.

"Using non-equine data effectively is somewhat challenging. A horse may be comparable to a ruminant in the role of a forage grazing animal, but it has a gastrointestinal tract more closely related to the pig."

Mycotoxins are a concern for horses because of the effects that consistent, low-level exposure may have on athletic performance and breeding capability, even without the appearance of any specific symptoms. Unlike commercially bred livestock, horses can have a long lifespan and may therefore be expected to reproduce successfully in their later years. For this reason, the relative “safe” level of mycotoxins allowable within the equine diet is unknown.

Acute mycotoxicosis (mycotoxin poisoning) is rare. The more common challenge for the horse is chronic mycotoxicosis, or repeated exposure to low levels of multiple mycotoxins. Mycotoxicosis has the potential to suppress the immune system and has been associated with a wide range of conditions, from general lack of form hypersensitivity and loss of well-being to colic, liver damage and even death. High-risk groups include horses whose immune systems may already be under pressure: broodmares, young stock, veterans, performance horses, poor doers or sick equids.

There are ways to reduce risk of mycotoxin contamination, however, through proper feed management and pasture management methods.

Feed management

Good management practices such as using quality feedstuffs, careful production and storage of feedstuffs, and ensuring a fully balanced diet can help reduce mycotoxin exposure.

But since many of the management practices that can reduce contamination occur during crop production and harvest, prevention is sometimes not an option for most horse owners who do not produce their own feed.

Extra care should therefore be taken when choosing feed to make sure that the producer stores ingredients properly. 

However, contamination is often unavoidable. One option for dealing with this is to include a mycotoxin adsorbent in the horse’s diet. It specifically binds mycotoxins and removes them from the gut. A mycotoxin adsorbent offers many advantages over alternatives such as clay binders, which require high inclusion rates and can remove key nutrients from the diet.

Pasture management

Grazing provides a significant source of both protein and energy.

When considering pasture from a mycotoxin management standpoint, the proportion of pasture contributing to the overall diet should be taken into account. Grass is most palatable in the early stages of growth, when sugar levels are highest, so getting the most out of a grazing system includes:


Allow time for each area to rest and regenerate some growth.

Divide your current pasture into smaller sections with suitable fencing to allow sufficient time for grass recovery and plenty of opportunity to rotate animals and provide fresh pasture.


Reduce old growth to promote the development of new growth.

Mow the pasture to a height of 6 to 8 inches immediately after removing horses, then allow four weeks for this section to recover before returning them.

Ideally, pastures should be mowed every three to four weeks to allow optimal growth and minimal weed development.

If you do not have the option to rotate horses, or if the pasture is too small to divide, designate a small area to feed hay while the pasture recovers. This will allow the majority of the pasture to recover.


Horses generally designate specific areas to drop manure; these areas are naturally avoided for grazing.

This can help to reduce parasite load, although worm larvae will travel a significant distance to find a healthy plant most likely to be consumed. Collecting and composting manure before spreading it back over the land kills worm eggs and allows valuable nutrients to enter the soil. Although parasite eggs are enclosed and can survive drying, they cannot survive heat above 80 degrees Fahrenheit, so composting eliminates them.

It also helps to reduce worm infestation when horses graze alongside other species. Use of fertilizer should be kept to a minimum, as horse manure is generally high in nitrogen and can act as sufficient fertilizer without over-dressing.

Undoubtedly, horses thrive in a situation where they have regular access to good pasture, both in terms of nutrient enrichment and company. However, poor attention to detail when planning management of grazing pastures can significantly increase the risk of mycotoxin contamination.

Horses cannot avoid exposure to mycotoxins, but with good management practices and the dietary inclusion of a proven mycotoxin adsorbent, it is possible to significantly reduce mycotoxins’ potentially harmful effects.

For more information on mycotoxins, visit knowmycotoxins.com or Alltech.com, or contact your local Alltech sales representative.