Metabolomic and proteomic changes in Standardbred horses in training

Metabolomic and proteomic changes in blood plasma were analysed in 16 young Standardbred horses from the age of 1.5 to 3.5 years. All horses had the same training programme from September as 1.5-year-olds until March as 2-year-olds, when highintensity training was introduced and the horses were divided into two training groups, High and Low. Both groups followed the same training programme, but the Low group performed 30% shorter high-intensity training distances than the High group. The same speed was aimed for with both groups. In blood samples collected from age 1.5 to 3.5 years, insulin-like growth factor 1 (IGF-1) was analysed with an ELISA kit, metabolomic profile was analysed using targeted absolute quantitative mass spectrometry and proteomic profile was analysed using untargeted mass spectrometry. There was no significant difference in IGF-1 between the training groups, but the expected ongoing IGF-1 decline was interrupted at a time which coincided with the onset of high-intensity training. Metabolomic differences between the training groups were only observed at 2 years of age, but concentrations of several metabolites changed significantly over time compared with at 1.5 years of age. Metabolites that differed significantly between the training groups and over time are associated with aerobic energy production and amino acid metabolism, and potentially also pH-buffering and vascular responses. The proteomics data did not reveal any significant differences between the training groups but the concentrations of 17 proteins related to energy metabolism, bone formation and circulatory functions changed significantly over time. In summary, both the metabolomic and proteomic profile in young horses in training changed over time, while the metabolic profile was also affected by training programme.