Use of mRNA Expression and Serum Biomarkers as Tools to Monitor Musculoskeletal Adaptation in Thoroughbred Horses Returning to Race Training

Scientific Abstract: Our duty to care for and heightened public awareness of racehorses has led to increased pressure for additional research into racehorse well-being and injury prevention. While immense efforts are being employed to identify racehorses at risk for catastrophic injury, these approaches are costly and logistically difficult for large numbers of horses. An additional area that requires focused research is in identifying and preventing non-fatal injuries given the direct link between previous lameness and/or being placed on a “vet list” and the risk of fatal injury. As such, a critical unmet need is the development of a sensitive and specific, minimally- invasive screening tool to pre-emptively identify horses at risk of injury. Epidemiological studies have demonstrated that racehorses returning following a layoff/spell, a process often called ‘reconditioning’, are at a significantly increased risk for injury as they return to training and racing due to bone de-adaptation when the stresses of race training are removed. Racehorses being imported into Hong Kong provide an important opportunity to monitor horses during reconditioning, where approximately 20% will experience an injury within the first 3-4 months following import. Based on our prior and ongoing work, we believe that mRNA expression analysis with cortisol and bone biomarker measurements could provide a sensitive means for identifying racehorses whose skeletons are not coping with training and are at risk of injury such that intervention prior to injury may be possible. Before the possibility of utilizing all of these modalities can be fully explored, however, it is imperative that we gain a better understanding of the typical and atypical responses of horses in training. We hypothesize that mRNA analysis with cortisol and bone biomarker measurements can be utilized to monitor racehorses in training and identify those at risk for poor performance and/or injury. Weekly veterinary examinations and trainer feedback will identify horses with signs of lameness/injury/illness or performance concerns while additional records will be collected for inclusion in data analysis. All aims of this project will utilize regularly collected blood samples from 80 previously trained +/- raced Thoroughbred horses that undergo a substantial period of deconditioning during importation quarantine for Hong Kong, followed by retraining/reconditioning in Hong Kong. Initially, Aim 1 will entail RNA-sequencing of a subset of matched injured and non-injured horses to identify mRNA targets of interest. Subsequent to this, mRNA from all samples will be analyzed via quantitative PCR (Aim 2) while serum will be analyzed for cortisol, CTX-1, and osteocalcin concentrations (Aim 3). Ultimately, this project will provide essential data to improve the welfare of horses not only entering Hong Kong, but across the globe. A critical step in this process is to better understand the responses of equine athletes to conditioning and reconditioning using a robust mRNA platform and serum biomarkers that have proven useful for identifying fracture risk. Data collected during this project will serve as important building blocks for future projects as we strive for better methods to reliably detect and prevent injuries in Thoroughbred racehorses.