How mycotoxins are produced

Under certain conditions molds are able to produce mycotoxins. These compounds are often produced in an attempt to ward off other organisms that might feed on the mold or to clear an area nearby to allow the mold room for growth. Molds must be present to produce mycotoxins, but once produced, the mycotoxin can remain in the environment with no mold present. Absence of mold, therefore, does not mean absence of mycotoxin.


What are mycotoxins?

Mycotoxins produced by molds or fungi can affect various animals upon ingestion or inhalation and can cause a wide variety of adverse clinical conditions. The condition and degree of adversity varies and depends on the nature and concentration of the toxin or toxins present, duration of exposure, species, age, as well as the nutritional and health status of the animal. It is important to understand that almost always more than one mycotoxin is present. This co-occurrence of various mycotoxins leads to synergistic effects and to more pronounced health effects.

Mycotoxins can be found in nearly all agricultural commodities, such as cereals (corn, wheat, oats and barley) and cereal by-products, in hay, and in bedding such as straw.

Ingesting mycotoxin contaminated feedstuffs

Upon ingestion, horses seem to be very sensitive to a range of mycotoxins. Horses are prone to the effects of these mycotoxins due to the fact that they do not have a defense mechanism such as the rumen in the cow. The microbial flora in the cow’s rumen degrades and deactivates many mycotoxins effectively into non-toxic substances. The gastric juices of the horse’s stomach do little to deactivate mycotoxins, thus they pass from the stomach into the small intestine where they can affect the gut wall or be absorbed into the blood stream.

When inhaled or ingested in large enough numbers, these can cause inflammation and irritation of the small airways in horses, leading to poor performance, reduced oxygen intake, and possible bleeding.

The effects of mycotoxins in horses can be amplified by performance and production stresses. Horses in training and competition, breeding mares and stallions, and rapidly growing foals are more susceptible to mycotoxins than horses used for less rigorous recreational riding or just being stabled. Their immune competency may be compromised, their nutritional requirements may not be fully met and so they need to consume more concentrates.

How is the horse affected?

Mycotoxins have been implicated in a variety of health problems including colic, neurological disorders, abnormal liver function, hypersensitivity, and brain lesions. Long term exposure of horses to low levels of mycotoxins may result in immune suppression, reduced growth rate, impaired feed conversion, mare fertility problems, frequent respiratory problems, reduced performance, and higher incidence of laminitis. In most cases these problems are considered to be caused by reasons other than mycotoxins. Hence, mycotoxins often are not recognized as the real trigger or at least as an important co-factor in the incidence of these conditions.

Controlling mycotoxin exposure

Correct storage of feeds and feedstuffs is critical in preventing mold growth. Feed should always be stored away from direct light and in a well-ventilated area. It is vital that feed never gets damp. Storage containers should be cleaned on a regular basis and the feed used completely before adding fresh feed. Signs of mold in feed include dustiness, caking of feed, feed refusal by animals for no apparent reason and a moldy, mildew smell.

Barn surfaces, feeding utensils and equipment, feed storage areas and feed tubs are reservoirs for infection and should be routinely cleaned and disinfected.


Molds and mycotoxins are naturally occurring and have always been in existence. Horses have been in their presence forever and will continue to do so. Minimizing exposure involves minimizing development of molds and mycotoxins in feedstuffs and forages during storage and feeding.

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