Preliminary insights on the daily rhythm of CRP and IL-6 in athletic horses

Background: Homeostasis and inflammation are two opposing physiological processes that are driven by the circadian clock. Aims/objectives: The study aim was to investigate the biological rhythm of the C-reactive protein (CRP) and Interleukin-6 (IL-6) in horses. Methods: Eight clinically healthy Italian saddle gelding horses, housed in individual boxes and subjected to a natural 12/12 L/D cycle, were enrolled. Blood samples were performed every 4 hours over a 48-hour period. Results: A positive correlation was found between CRP and IL-6 on both days of monitoring. Both parameters showed a daily rhythm; CRP acrophase was in the middle of the scotophase, IL-6 acrophase at the beginning of the light phase, and both parameters had a high percentage of robustness (>75%). Conclusion: This preliminary information improves the knowledge about the daily rhythm and possible correlation of some inflammatory biomarkers in horses. Further studies are necessary to investigate how different environmental conditions, management, and physical exercise might influence this rhythmicity.