Effects of High-Speed Training on Messenger RNA Expression in Two-Year-Old Thoroughbred Racehorses

Abstract

Accumulating high-speed exercise has been identified as a significant risk factor for catastrophic injuries in racing Thoroughbreds. Injuries, regardless of severity, are a main cause of withdrawal from the racing industry, raising animal welfare concerns and resulting in significant economic losses. While most of the current literature focuses on catastrophic injuries incurred during racing rather than training, the present study aims to help fill this gap as well as discuss the associated risk factors. The evaluation of messenger RNA (mRNA) expression changes provides an efficient and straightforward approach to identifying horses at risk for catastrophic injury. While alternative injury risk assessment methods, such as Positron Emission Tomography and other advanced imaging techniques, have been investigated, they present accessibility concerns when evaluating cost, availability, and complexity. As such, peripheral blood was collected weekly, prior to exercise or administration of medication, from eighteen, two-year-old Thoroughbreds throughout their first season of race training. Messenger RNA was isolated from these samples and used to analyze the expression of 34 genes via RT-qPCR. Statistical analysis of the non-injured horses (n=6) showed that 13 genes were significantly associated with increasing average weekly furlong performance while CXCL1, IGFBP3, and MPOhad negative correlations with cumulative high-speed furlongs and week of training for both injured and non-injured groups. Comparison of both groups identified opposing correlations between an anti-inflammatory composite index (IL1RN, IL-10, and PTGS1) and average weekly furlong performance. Furthermore, evaluation of training effects on mRNA expression during the weeks surrounding injury identified differences between groups in IL-13 and MMP9 at -3 and -2 weeks prior to injury. While some previously reported relationships between exercise adaptation and mRNA expression were not noted in this study, this may have been due to the small sample size. Several novel correlations, however, were identified and warrant further investigation as markers of exercise adaptation or potential risk for injury

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