Study reveals horses can ingest banned steroid from everyday feedstuffs
A two-year research investigation led by QUT has revealed horses can be exposed to a banned anabolic steroid through hay and pasture weeds, potentially causing positive drug tests for innocent riders and horses.
Ecdysterone (20-hydroxyecdysone) is a natural plant extract used by body builders to promote muscle strength and 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 has now found environmental exposure could be a cause of the steroid's detection in horses.
The research journey began in 2023 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 Professor Sillence, Associate Professor Kathi Holt and Dr Ivy Li – all from the QUT School of Biology and Environmental Science – and Dr Pat Harris (Waltham Petcare Science Institute, UK), Mitchell Coyle (UQ) and Dr Danielle Fitzgerald (UQ).
“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 and 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.
“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.
“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 which encourages members to take every reasonable precaution to reduce the risk of feed and supplement contamination.”
Professor Sillence is one of Australia’s leading equine scientists with four decades of research across the fields of veterinary and animal science.
Photo at top of page: Dr Ivy Li, Associate Professor Kathi Holt and Professor Martin Sillence with plant samples in the lab.
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