Transcriptomic signatures reveal systemic adaptations and immune modulation in response to training and competitive racing in horses.

backgroundThe molecular mechanisms underlying adaptation to physical exertion and racing stress in horses remain incompletely understood. Peripheral blood transcriptomics offers a minimally invasive method to monitor systemic responses to exercise and identify biomarkers of adaptation or overload.

objectivesTo evaluate transcriptomic changes in peripheral blood of racehorses during different phases of training and competition and to identify molecular markers of physiological adaptation and race-induced stress. STUDY

designProspective transcriptomic profiling of trained racehorses across three exercise conditions.

methodsForty racehorses (29 Arabian, 11 Thoroughbred) were sampled before (p0) and after (p1) exercise at three stages: initial training (T1), mid-season training (T2) and racing (R). RNA-seq was performed, followed by differential expression analysis (DESeq2) and pathway enrichment (g:Profiler, DAVID). Identified differentially expressed genes were integrated into STRING protein-protein interaction condition-exclusive subnetworks (Merge tool in Cytoscape) to compare the transcriptomes between conditions.

resultsDistinct molecular programmes were identified at each stage. At T1, immediate-early response genes such as FOS, FOSB and HSPA6 were strongly up-regulated, reflecting acute stress and immune activation. At T2, immune-related transcripts (KLRD1, CCL4, PRF1) remained enriched, but genes linked to remodelling and adaptation, including DNAJA1, HSPH1 and CXCR4, became prominent, suggesting a shift toward recovery and regulatory processes. Post-race, chemokines such as CCL5 and stress markers (HSP90 family, JUN) were highly induced, accompanied by widespread transcriptomic divergence and down-regulation of certain immune regulators (IL18, ARHGAP44), indicating both heightened innate activation and transient immune suppression. MAIN LIMITATIONS: Transcriptomic profiling was limited to peripheral blood, which may not reflect tissue-specific responses. Only three sampling points were included, potentially overlooking transient transcriptomic changes.

conclusionsTranscriptomic dynamics in blood reflect the transition from early immune activation (T1), through adaptation (T2), to stress-related activation post-race (R). This approach offers promising molecular biomarkers for monitoring training adaptation and detecting physiological overload in equine athletes.