The Mycotoxin Problem

There can be a number of reasons why a horse might have performance problems. A diagnosis can be frustrating, but one reason that might be overlooked is mycotoxicosis. It wasn’t until recently that the significance of mycotoxins was realized, said Thomas Buckley, MS, head of microbiology at the Irish Equine Centre. Buckley presented “Coping With Mycotoxin Contamination: Protecting Equine Performance and Health” at the sixth annual Equine School at the Alltech Symposium held in Lexington, Ky. Buckley said The problem of mycotoxicosis costs millions of dollars annually for the Irish horse industry.

This topic was particularly important to horse breeders in Kentucky the past couple of years when mycotoxins were under scrutiny as potential contributing factors in mare reproductive loss syndrome (MRLS). Extensive testing of Kentucky horse pasture during 2002 did not detect any levels of mycotoxins in most pasture fields. Where mycotoxins were detected, it was at very low levels, and these were not correlated to MRLS.

When molds and fungi exude poisons called mycotoxins as part of their metabolism and the horse ingests or breathes in these molds/fungi and mycotoxins, serious health problems (including death) can result. Mycotoxins can be found in feed, pastures, bedding, on stable equipment, and even in the air and on cobwebs. They are sometimes very difficult to detect. Due to the seriousness of mycotoxicosis, one of the prime functions of the Irish Equine Centre was to identify the source of mold infections and their mycotoxins.

Mycotoxicosis can result in reproductive, gastrointestinal, and respiratory problems in the horse and other livestock. By suppressing the immune system, these mycotoxins can result in secondary disease such as bacterial or parasitic infections. Respiratory problems--such as chronic obstructive pulmonary disease (COPD), exercise-induced pulmonary hemorrhage (EIPH), and infectious respiratory disease--can be induced or exacerbated by mycotoxins.

Unfortunately, drug treatments have little effect on mycotoxicosis, therefore “we must treat the cause, not the effect,” said Buckley.

Buckley said that the most important toxigenic fungi are species of the Aspergillus, Fusarium, and Penicillium genera. Apergillus species produce aflotoxins, which are potent liver toxins and are known to be carcinogenic, said Buckley. COPD, a delayed hypersensitivity reaction to inhaled allergens, has been associated with fungal spores produced by A. fumigatus. These spores can be found on hay, shavings, and straw.

Fusarium species are pathogens of plants, such as cereal grains. According to Buckley, the most important fusariotoxins are fumonisins, fusaric acid, zearalenone and it’s derivatives, and the trichothecenes.

A variety of factors can cause excessive mold growth. If a forage or feed is subjected to high moisture content for an extended period of time or subjected to inadequate processing or storage, then mold can take hold. Feed and bedding moisture content is the most problematic cause of mycotoxicosis, said Buckley. Anything over 11% moisture content can cause problems, and on many farms, by the time feed reaches the animal, it can contain more than 20% moisture. Therefore, Buckley said that soaking feed overnight can have its pitfalls. He recommends sprinkling hay with water rather than soaking it. In addition, drought or rain, followed by cold weather, can also stress plants and increase mold and fungi growth. Other factors include:

• pH changes;
• Humidity;
• Competition or interaction between fungi and other microorganisms; and
• Improper aeration.

He offered a few suggestions on how to reduce the risk of mold and fungi growth. Removing damp bedding on a regular basis is always advisable. In addition, a thorough steam cleaning might be useful. Make sure that feed is stored properly (such as in bins that seal well) and kept fresh. Don’t allow excess moisture in feed, and if feed is spoiled, do not feed it. Keep all equipment clean. Check the stable for ventilation problems and areas with excessive moisture. And, if at all possible, avoid the use of antibiotics.(A product manufactured by Alltech called Mycosorb, a mycotoxin binder, was top dressed on feed as a precaution against mycotoxins during the MRLS crisis.)

In a survey by the Irish Equine Centre of premises with known problems, samples were taken from a variety of sources and tested for the presence of Apergillus. Contaminated sites included walls, feed tubs and bins, floors, hay, dust, mixed feed in bins, buckets, and the air. Blood samples and bronchoalveolar lavages were taken by a veterinarian. On examination of the blood samples, about 60% of the horses had antigens to Aspergillus. In addition, horses had high total bilirubin, low globulin values, gut-related problems, anemia in some cases, elevated muscle enzymes, as well as displaying fatigue and poor performance or a lack of performance.

Buckley said that laboratory expertise for mycotoxin detection has developed significantly in Ireland in the past few years. “It is recognized now that the mycoses--diseases of fungal origin--are more common than before, and their incidence has increased through the widespread use of antibacterial agents and immunosuppressive drugs,” he said. “It is incumbent on microbiologists, therefore, to become more knowledgeable about the pathogenic fungi and their identifying characteristics.”

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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