Characterisation of high-intensity exercise during training using an untargeted metabolomics approach in thoroughbred flat racehorses

High-intensity exercise (HI) sessions are essential in thoroughbred (TB) flat racehorses training programs. This untargeted metabolomics study aimed at characterizing the metabolic response induced by HI in field conditions. Six TB racehorses performed a non-standardized HI according to their training program. Heart rate (HR), speed and distance were recorded. Blood samples were collected at rest, 5 minutes, 30 minutes and 120 minutes after exercise to monitor targeted biochemical parameters such as lactatemia, serum creatine kinase activity (CK) and acylcarnitines profile. Rest and 30 minutes after exercise plasma samples were analyzed using an untargeted metabolomic approach based on liquid chromatography coupled with mass spectrometry. Horses aged 2.5±0.6 years with varying racing histories (0 to 14 races) ran at 48.2±1.1 km/h for 1.4±0.5 km resulting in 203±8 bpm heart rate and a lactatemia of 8.1±1.5 mmol/L five minutes after exercise. Cortisol, insulin, creatinine, urea, CK, triglycerides and several acylcarnitines increased significantly, whereas beta-hydroxybutyrate decreased significantly after exercise (p < 0.05, Wilcoxon signed-rank test). Supervised analyses revealed HI-induced changes of 53 metabolites associated mainly with protein (58.5%), lipid (17.0%), nucleotide (11.3%) and vitamin (7.6%) metabolism. Metabolites of glutamate, tyrosine and tryptophan pathways were enriched. Metabolome changes were associated with routine biochemical modifications and provided an extended characterization of the physiological response to HI. Untargeted metabolomics has the potential to identify metabolites of interest to monitor horses’ response to training and could help to better understand the underlying mechanisms of overtraining and injury development