Horseracing is under increased scrutiny, especially due to recent clusters of fatal musculoskeletal injury (FMI) events at prominent racetracks. Aside from the unfortunate loss of equine life and risk to human jockeys, racehorse fatalities significantly impact public perception and lead to substantial economic losses for the equine industry. Fractures of the proximal sesamoid bones are the most common cause of racehorse fatality in New York, California, Kentucky, Florida and Hong Kong(1–6). While the epidemiology of FMI is complex and multi-factorial, there is widespread concern that recent clusters of fatalities may be due, in part, to the approval of the bisphosphonates clodronate (Osphos®) and tiludronate (Tildren®) in 2014. Bisphosphonates are known to interfere with the normal remodeling process of replacing old bone with new bone and result in increased microfractures in human bone. There is concern that bisphosphonates might impair the normal adaptive remodeling and repair processes in equine bone during race training. However, whether or not bisphosphonates are associated with equine FMI is an open question, and one that the racing industry needs to answer.

Whereas bisphosphonates can only be detected in serum and urine for a relatively short period of time (~30 days), these drugs significantly accumulate in bone, resulting in a long-term reservoir for continuous release of bisphosphonate for months to years, even after the medication is discontinued(8). Bone concentrations of tiludronate have been detected in horses for up to 1 year post-treatment(9), and the half-life of clodronate in rodent bone is estimated to be months to years. Although harvesting bone biopsies is not a realistic approach for screening for bisphosphonates in live racehorses, it is the ideal tissue for estimating how commonly bisphosphonates are administered to the racing population.

In Aim 1 of this proposal, a case control study, especially suited to the rapid acquisition of large data sets for investigating “rare” events such as FMI, will be employed to estimate how common bisphosphonate administration is in the young, exercising Thoroughbred racing population in New York using a sample of 82 animals that have already been acquired, plus an additional 100 animals that will be collected over the next year. Here, we propose to leverage Cornell University’s expertise in nuclear magnetic resonance (NMR) spectroscopy and SUNY-Morrisville/New York’s Equine Drug Testing and Research Program’s expertise in ultra-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) small molecule detection methods to identify bisphosphonates in equine bone tissues. This expertise, coupled with our access to a cohort of 66 TB racehorse cadaver bone samples (expected to be 82 by 4/1/20) that have been extensively characterized through advanced imaging approaches, including computed tomography (CT) and bone density and bone quality imaging methods, will enable us to address important questions about the effects of bisphosphonate administration on bone remodeling. In Aim 1.3, we will evaluate the effects of bisphosphonates on bone remodeling in the young racing Thoroughbred population, with ~50% of our cohort including 2- and 3-year old horses with complete training and racing exercise histories.

In Aim 2, we will apply similar techniques to determine how a single dose of the bisphosphonates clodronate and tiludronate results in detection of bisphosphonates in blood, urine, bone, hair and hoof tissues. While LC-MS/MS approaches can detect lower concentrations of bisphosphonates than NMR approaches, NMR is faster, less expensive, requires less sample preparation and may have value as a screening method. Furthermore, this Aim 2 dovetails with ongoing work in the New York Equine Drug Testing and Research Program laboratory directed towards improved method development for low-level detection of bisphosphonates in blood.

Optimization of techniques for measuring bisphosphonates will advance the current state-of-art in racing medication drug testing efforts. Our ultimate goal is to help racehorse veterinarians, owners and trainers make informed decisions about fracture risk while improving equine welfare, mitigating negative publicity, and enhancing our understanding of the impact of bisphosphonates on bone remodeling and fracture risk.