The Modern Equine Vet
August 2023
Vol 13 Issue 82023
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News Notes

Hair Samples Useful for Detecting Long-term Bisphosphonate Use in Horses

By Amy Young, UC Davis

Hair samples can be useful in detecting the long-term use of bisphosphonates in horses, according to a study by Heather Knych, DVM, PhD, of the K.L. Maddy Equine Analytical Chemistry Lab’s Pharmacology section and the Department of Molecular Biosciences, at U.C. Davis College of Veterinary medicine.

“From our previous research, we know that bis-phosphonates remain in equine bone over long periods,” Dr. Knych said. “Hair sampling is non-invasive and has proven to be a reliable and reproducible matrix for equine drug testing. The ability to detect bisphosphonates long term in hair samples would benefit horse welfare and the integrity of the sport.”

The current study developed an assay and evaluated the use of hair for long-term detection of the bisphosphonate, clodronate. Results indicated that the drug was detectable in hair for up to 6 months in most of the horses studied. Further research is needed to better understand how long it takes clodronate to be incorporated into hair, as well as implications for widespread use of this testing method.

Bisphosphonates are molecules that strongly bind to bone material and prevent bone resorption and natural remodeling. Two bisphosphonates are approved for use in horses that are 4 years of age and older, clodronate disodium (Osphos) and tiludronate disodium (Tildren). They are safe and effective at relieving pain and lameness in horses with navicular syndrome.

However, off-label use to treat other equine bone conditions, especially in young horses, has raised concerns about long-term effects on bone, and weakened bones can put horses at risk for catastrophic injuries. The Horseracing Integrity and Safety Authority’s Anti-Doping and Medication Control program has categorized bisphosphonates as banned substances. Horses that test positive under the program are subject to lifetime racing ineligibility.

Previous studies by Dr. Knych’s group reported that bisphosphonates can be detected in equine bone, blood and urine for extended periods. However, their results also showed that detection in blood and urine can be inconsistent. Compounds can generally be detected for much longer periods in hair than in blood or urine. As such, mane and tail hair samples can provide long-term historical records of drug exposures.

Important Tool
“Hair testing has become an increasingly important anti-doping matrix in horse racing, but not all prohibited substances are amenable to hair testing,” said Rick Arthur, DVM, a former Equine Medical Director and a co-author on the study.

“Regulators are keen to expand their understanding of which drugs of interest can be detected in hair and under what conditions. This study is an example of that effort. Anti-doping in horse racing not only addresses performance enhancing or other performance modifying substances, but horse health and welfare substances as well. Bisphosphonate misuse has been a major concern for horse safety, and now hair testing offers an alternative matrix to blood and urine,” Dr. Arthur said.

The study was supported by a special call for bisphosphonate research from the Grayson Jockey Club Foundation. MeV

The article was originally posted here: It was edited for style and length.


Knych K, McKemie DS, Yim S, et al. Long-term monitoring of clodronate in equine hair using liquid chromatography-tandem mass spectrometry. J Chromatogr B Biomed Appl. 2023;1226: 123789. Published July 15.