39 Effect of high-speed training in 2-year-old Thoroughbreds on select mRNA expression

Abstract

The accumulation of increased distances covered during high-speed exercise has been identified as a significant risk factor for catastrophic injuries in racing Thoroughbreds. Injuries, both fatal and non-fatal, are one of the main causes of horses leaving the racing industry, resulting in animal welfare concerns and economic losses. While most of the current literature focuses more on injuries incurred during races than training, the present study aims to help fill this gap, as well as several others, in the current literature. To achieve this goal, peripheral blood was collected weekly into Tempus Blood RNA Tubes from 21, 2-year-old Thoroughbreds for the duration of their first season of race training (20+ weeks). Samples were collected before exercise or the administration of medication. Messenger RNA (mRNA) was subsequently isolated and the expression of 36 genes analyzed via RT-qPCR. These 36 genes were selected for their involvement in inflammation, tissue and bone repair, injury response, and ongoing RNA-sequencing research with catastrophically injured Thoroughbreds. For this aim of the larger project, statistical analysis was performed using a subset of horses (n = 6, 5 colts and 1 filly) that did not incur injuries during the study. Within this group, correlations between gene expression and cumulative high-speed furlongs (CHSF, with ‘high-speed’ categorized as galloping at speeds of 15 s/furlong or less)or week of training were evaluated using Pearson Correlation. While all genes were analyzed individually, the average expression of certain genes was also combined to form pro-inflammatory and anti-inflammatory indices. Only correlations with a correlation coefficient of less than −0.3 or greater than 0.3 and a P < 0.0001 were considered significant. A total of 5 genes (CXCL1, IGFBP3, IL-10, MPO, and TLR4), as well as the anti-inflammatory index, demonstrated relationships of significance correlated with CHSF. Of these, TLR4, IL-10 and the anti-inflammatory index had a positive correlation while MPO, CXCL1, and IGFBP3 had a negative correlation between the 2 variables. Additionally, 5 genes (CXCL1, IGFBP3, MPO, TLR4, and TNNC2) were found to significantly correlate to the week of training, in which TLR4 was positively correlated and CXCL1, MPO, IGFBP3, and TNNC2 were negatively correlated. While some previously reported relationships between exercise adaptation and mRNA expression were not noted within this study, this could be due to the small sample size. Regardless, several of the correlations identified in this preliminary work are novel and warrant further investigation as markers of fitness or potential risk for injury.