A two-year research investigation led by Queensland University of Technology (QUT) in Australia revealed that horses can be exposed to a banned anabolic steroid (ecdysterone) through hay and pasture weeds. This can potentially cause positive drug tests for innocent riders and horses.

Ecdysterone (20-hydroxyecdysone) is a natural plant extract used by body builders to promote muscle strength. Detection in certain equestrian competitions has resulted in an automatic suspension for riders and fines for horse owners and trainers.

But, a team of equine scientists led by QUT’s Professor Martin Sillence found that environmental exposure could be a cause of the steroid’s detection in horses.

Dr. Ivy Li with one of the lambsquarters samples. Courtesy Anthony Weate, QUTMedia

Research on Ecdysterone

The research journey began in 2023. This was after Professor Sillence was contacted about an Australian rider whose horse had failed a drug test.

The scientists’ rigorous testing and published results found:

  • Ecdysterone in all 24 hay samples tested from across four Australian states (Queensland, New South Wales, Victoria, and Tasmania).
  • Extremely high levels in weeds such as lambsquarters and black nightshade.
  • The presence of ecdysterone at low concentrations in several commercial horse feeds and supplements.
  • Persistently high ecdysterone levels in some horses, despite having access to the same feed as others.
  • Significant individual variation in how horses absorb and respond to ecdysterone, with some showing blood levels up to 30 times higher than others after the same dose.
  • Internal parasites might also contribute to ecdysterone in a horse’s system.

The study has been published in the journal Animals and was co-authored by a group of professionals. Those included Professor Sillence, Associate Professor Kathi Holt, and Dr Ivy Li, all from the QUT School of Biology and Environmental Science. Others included Dr. Pat Harris (Waltham Petcare Science Institute, UK), Mitchell Coyle (UQ), and Dr. Danielle Fitzgerald (UQ).

From left: Dr Ivy Li, Professor Martin Sillence, and Associate Professor Kathi Holt at QUT. Courtesy Anthony Weate, QUTMedia

Comments by Professor Sillence

“National and international equestrian authorities who treat ecdysterone as a banned substance with no limit of reporting will need to reconsider their rules and allow for the possibility that not all positive tests are the result of cheating, but may occur due to unintended environmental exposure,” Professor Sillence said.

“These changes will be essential to protect innocent competitors. While they would not absolve persons responsible for the horse from all liability, there would be a credible argument for a judgement of no fault—no penalty,” he continued.

Professor Martin Sillence in the lab. Courtesy Anthony Weate, QUTMedia

“The issue of naturally-occurring prohibited substances is significant for horse owners, trainers, riders, and veterinarians, and we urge them to take note of our findings regarding ecdysterone and other substances that can find their way into a horse by accident,” added Professor Sillence. “Such exposure is likely to become increasingly common as climate change affects the distribution of various plants and weeds. For example, in the UK, members of the nightshade family—which contain the prohibited substances atropine and hyoscine—are becoming increasingly common in feed crops.

“We would also like to see Australia adopt appropriate standards such as those set out by the British Equestrian Trade Association,” said Professor Sillence. “[These standards] encourage members to take every reasonable precaution to reduce the risk of feed and supplement contamination.” (Editor’s note: See links under Further Content below.)

About Professor Sillence

Professor Sillence is one of Australia’s leading equine scientists with four decades of research across the fields of veterinary and animal science.

For more information contact QUT Media contacts Mechelle McMahon at media@qut.edu.au.

Further Content

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