# Sources of Environmental Exposure to the Naturally Occurring Anabolic Steroid Ecdysterone in Horses

## TL;DR

This study investigates how horses can accidentally ingest ecdysterone, a banned substance, through their diet or parasites, which could lead to unfair drug test results.

## Contribution

The study identifies environmental sources of ecdysterone exposure in horses and reveals significant individual variability in blood concentrations after ingestion.

## Key findings

- Ecdysterone was detected in hay and weeds like Chenopodium album and Solanum nigrum at concentrations up to 244 µg/g.
- Horses with parasite infestations showed higher faecal ecdysterone levels, but anthelmintic treatment did not reduce concentrations.
- Some horses exhibited unusually high and prolonged serum ecdysterone levels after oral administration, indicating individual variability.

## Abstract

Ecdysterone is a natural plant extract which is used by body builders to promote muscle strength and is undergoing clinical trials for muscle wasting in elderly people. It could also be a useful treatment for aged, retired horses, but is banned for use in competition. Currently, there is no minimum threshold for reporting the presence of ecdysterone, and positive findings for the drug have caused significant controversy. As there have been no previous studies in horses, data on the sources of environmental exposure and on the concentration of naturally acquired ecdysterone in this species are urgently needed to inform new rules of competition and to protect owners, riders, and trainers from unfair sanctions. This study explored the risk of unintended exposure through the ingestion of hay, pasture plants, and the presence of internal parasites. The results demonstrate that competition horses could be at risk of adverse analytical findings through either accidental dietary exposure or parasite infestation. Furthermore, we have discovered that some horses may be at extreme risk because their blood ecdysterone concentrations are much higher than those found in other horses, after consuming the same amount of ecdysterone. These factors need to be considered carefully when designing ecdysterone treatment regimens and when setting a reporting threshold in equine sports.

Ecdysterone controls moulting and reproduction in insects, crustaceans, and helminths. It is also produced by many plants, probably as an insect deterrent. The steroid is not made by vertebrates but has anabolic effects in mammals and could be useful for treating sarcopenia in aged horses. However, ecdysterone is banned in horseracing and equestrian sports, and with no limit of reporting, the risk of unintended exposure to this naturally occurring prohibited substance is a concern. To explore this risk, pasture plants and hay samples were analysed for ecdysterone content, as well as samples of blood, faeces, and intestinal mucosa from horses (euthanized for non-research purposes) with varying degrees of endo-parasite infestation. The variability in serum ecdysterone concentrations between different horses after administering a fixed dose was also examined. Ecdysterone was detected in 24 hay samples (0.09 to 3.74 µg/g) and several weeds, with particularly high concentrations in Chenopodium album (244 µg/g) and Solanum nigrum (233 µg/g). There was a positive correlation between faecal ecdysterone and faecal egg counts, but no effect of anthelmintic treatment and no relation to the number of encysted cyathostome larvae in the large intestine mucosa. Certain horses maintained an unusually high serum ecdysterone concentration over several weeks and/or displayed an abnormally large response to oral ecdysterone administration. Thus, the risk of environmental exposure to ecdysterone is apparent, and several factors must be considered when determining an appropriate dosage for clinical studies or setting a reporting threshold for equine sports.