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Holistic Horse Issue 112

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Leading figures in the equine industry agree: The exposure of horses to mycotoxins, or toxins derived from mold, 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?

Horses can be exposed to mycotoxins via feed materials, grazing, and bedding. Mycotoxins are produced by some types of mold growth under certain conditions. They can occur in growing, harvested or stored grain and forage crops.

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 due to extreme weather conditions or heavy grazing. The prevalence of mycotoxins is usually highest from plants grazed or harvested during a wet autumn following a dry summer.

Until recently, there has been limited research surrounding the effects of mycotoxins on horses, with data usually used from the swine or ruminant industries. It is somewhat challenging to use non-equine data effectively, as a horse is comparable to a ruminant in the role of a forage grazing animal but has a gastrointestinal tract more closely related to a pig’s. The addition of the hindgut fermentation process may also be a complication. The requirements for a horse are also significantly different from those for livestock species. The focus for equines is less on meat and milk production and more on conformation, temperament, performance, and durability.

Mycotoxins are a concern for horses because of the effects that consistent, low-level exposure may have on athletic performance and breeding capability without the appearance of any specific symptoms. Horses can also 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 likely challenge for the horse is chronic mycotoxicosis, or 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.

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

Therefore, extra care should be taken when choosing feed to ensure ingredients have been stored and mixed appropriately. When storing feed at home or the yard, clean, dry, and water-tight containers should be used. They should be cleaned between feeds and should be vermin-proof. All feeding equipment and utensils should also be cleaned regularly and stored in a cool, dry area. Despite these precautions, contamination is often unavoidable. One option for dealing with this is to include a mycotoxin adsorbent in the horse’s diet, as it specifically binds
mycotoxins and removes them from the gut. Traditionally, clay binders have been included in the diet for this purpose. However, they tend to have high dietary inclusion rates and can also bind key nutrients from the diet. Organic mycotoxin adsorbents, such as yeast cellwall fractions, offer many advantages over the clay binders, including lower inclusion rates and rapid binding of mycotoxins—without binding key dietary nutrients. As such, many of these organic mycotoxin adsorbents can be used regularly used in a horse’s diet.

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