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Molds: Possible Cause of Positive Equine Drug TestsBy Kentucky Equine Research Staff · August 18, 2016

Molds get a bad rap in the equine industry and justifiably so. Inhalation of molds contribute to equine asthma syndrome, which includes inflammatory airway disease and heaves, and ingestion of molds can result in poisoning. Now, researchers believe* that some molds can also produce testosterone-like substances from plant-based steroids. The result? Potentially a positive drug test for competitive horses.

“Some molds and bacteria are capable of a process called ‘biotransformation’ that results in the production of steroids or steroid precursors from plant products,” explained Kathleen Crandell, Ph.D., an equine nutritionist with Kentucky Equine Research (KER).

After horses ingest feeds that contain these types of molds, the steroids are subsequently detectable in the urine. In the case of competitive horses, there is a zero-tolerance policy for such compounds, and serious consequences, such as fines and suspensions, ensue.

Anabolic steroids, like testosterone, are performance enhancers that give athletes an unfair advantage over their competitors and have important welfare issues. In some cases, horses have tested positive for anabolic steroids despite the owner or trainer denying their administration.

To determine if consumption of moldy feed is responsible for these false positives, researchers tested various moldy feeds. Of all the feeds tested, only moldy corn had detectable levels of an anabolic steroid that could have resulted in a false-positive drug test. In addition, one herbal phytosupplement also contained alpha-testosterone.

The researchers noted, “These results demonstrate that it is important to caution against the consumption of any feed or (herbal) supplement of which the detailed ingredients and quantitative analysis are unknown. The consumption of moldy corn should especially be avoided, not only from a horse health and welfare point of view, but also to avoid possible inadvertent positive doping results.”

Crandell added, “These findings underscore the importance of using only quality horse feeds from reputable manufacturers, such as KER Partner Feed companies, that test corn for mold coming into the facility before using it in any horse feeds.”

*Decloedt, A.I., L. Bailly-Chouriberry, J. Vanden Bussche, et al. 2016. Mouldy feed: A possible explanation for the excretion of anabolic-androgenic steroids in horses. Drug Testing and Analysis. 8:525-534.