A new study was published in America on the use of hair as a matrix for the long-term detection of bisphosphonates in horses. The study was in response to a special call for bisphosphonate research by charitable organisation the Grayson-Jockey Club Research Foundation who support equine veterinary research at universities in North America and elsewhere.

“Over the past few years, bisphosphonate use has become a concern with regard to the welfare of thoroughbred racehorses,” said Jamie Haydon, president of Grayson.

“Bisphosphonates are labelled for horses four years and older to manage navicular symptoms,” said Dr Johnny Smith, research chair of Grayson. “Unfortunately, people were using them in young horses, which is detrimental because bisphosphonates inhibit bone resorption, can stay in a horse’s system for years, and can have long-term effects on bone.”

There are concerns regarding impairment of normal physiological functions including growth, bone repair, and bone remodelling, especially in juvenile and exercising animals. Additional research must focus on identifying the short-term and long-term effects of bisphosphonates in young and exercising animals to ensure the efficacious and judicious use of this powerful, long-lasting group of drugs.

The American Food and Drug Administration (FDA) describes phosphates as: “A class of drugs commonly prescribed to prevent bone loss in people. While Tildren and Osphos are not used for this purpose in horses, knowing how bisphosphonates work in people will help you better understand this drug class overall and especially the adverse reactions seen in horses.

“Bones undergo constant turnover, with osteoblasts forming bone and osteoclasts resorbing it. In normal bone tissue, there is a balance between bone formation and bone resorption. But in diseased bone tissue, this balance is disrupted. Bisphosphonates inhibit bone resorption by causing osteoclasts to undergo cell death, leading to a decrease in the breakdown of bone.

“Bisphosphonates preferentially “stick” to calcium and bind to it. Because most of the body’s calcium is stored in bones, these drugs accumulate to a high concentration only in bones. Bisphosphonates are incorporated into the bone matrix and are gradually released over months to years.”

The new study found that hair testing can be used to consistently detect bisphosphonates for up to six months after administration. Previously published studies, including one conducted by the same group and funded under the same special call, demonstrated that in some cases bisphosphonates can be detected in blood and urine for extended periods of time, but detection using these matrices can be unpredictable and less consistent.

The FDA study from 2020 showed that clodronate and tiludronate reside in the bone for extended periods.

“This can lead to lasting pharmacologic effects and increase the risks of injury to racehorses.” explained the study’s principal investigator, Dr Heather K. Knych, from the School of Veterinary Medicine at the University of California, Davis.

“Being able to detect bisphosphonates long term in hair benefits the athletes and increases the integrity of the sport.”

Bisphosphonates are considered a banned substance for covered horses under the Horseracing Integrity and Safety Authority’s Anti-Doping and Medication Control programme in America. A covered horse that tests positive is subject to lifetime ineligibility.

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