Comparison of pre-race inflammatory marker mRNA expression with race-related parameters in thoroughbreds

Research in Thoroughbred racehorses has demonstrated continual training leads to a decrease in pro-inflammatory gene expression as horses become race fit, although not all horses experience this predicted decrease. Here, the goal was to determine whether pre-race inflammatory marker mRNA expression correlates with race performance and other horse-specific parameters. Single blood samples in Tempus RNA stabilisation tubes were collected during pre-race total CO₂ testing at a Thoroughbred racetrack in Kentucky. mRNA was isolated and quantitative PCR performed on the samples for the pro-inflammatory markers interleukin (IL)-1β, IL-6, IL-8, IL-17, and tumour necrosis factor (TNF)-α. Expression data was analysed using one-way ANOVA on Ranks. There was no predictive value of inflammatory marker expression for race performance other than decreased IL-6 in race favourites that finished in the top three positions. Horses entered into graded stakes races had significantly lower expression of pro-inflammatory cytokines IL-1β and TNF-α, as well as a lower average of all 5 markers combined, when compared to allowance and claiming horses. Additionally, some claiming horses had evidence of increased pro-inflammatory marker expression. Lower inflammatory marker expression in graded stakes horses likely arose from both the fitness level and management practices of these horses, as these horses had a lower number of and greater interval between starts when compared to claiming and allowance horses. Evidence of increased inflammatory marker expression in some horses would suggest that they are not sufficiently conditioned or recovered fully between races or bouts of high-speed training. While there were other significant differences detected, their biological importance remains unclear.