Immune Response in Young Thoroughbred Racehorses under Training

Area of Science:

• Equine physiology
• Exercise immunology
• Sports science

Background:

• Athletic training acts as a stressor, initiating innate immune responses and inflammation to restore homeostasis.
• Thoroughbred racehorses, with their standardized training and genetics, serve as a valuable model for studying these physiological changes.

Purpose of the Study:

• To investigate the innate immune response and inflammation in young, untrained Thoroughbred racehorses during their initial training season.
• To analyze haematological and molecular alterations associated with the first 3 months of sprint exercise training.

Main Methods:

• Twenty-nine Thoroughbred racehorses were monitored over a 3-month incremental sprint exercise schedule.
• Blood samples were collected at baseline (T0), 30 days (T30), and 90 days (T90) for haematological analysis.
• Gene expression of key inflammatory cytokines (IL-1β, IL-4, IL-6, IL-2, IL-3, IL-5, IL-8, TGF-β, TNF-α, IFN-γ) was assessed using RT-qPCR.

Main Results:

• Significant increases in mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and haemoglobin concentration (MCHC) indicated enhanced oxygen transport capacity.
• Changes in white blood cell counts, specifically increased basophils and eosinophils, were observed at T30 and T90, respectively.
• Differential gene expression of inflammatory cytokines was noted, with upregulation of IL-2, IL-4, IL-8, IL-1β, and IL-3, and downregulation of TGF-β and IL-5, while IFN-γ and TNF-α showed no significant changes.

Conclusions:

• The study demonstrates long-term physiological adjustments in oxygen transport capability in response to exercise adaptation in young racehorses.
• Alterations in granulocyte counts and inflammatory cytokine gene expression highlight the significant role of the innate immune system during training stress.
• These findings provide insights into the complex interplay between exercise, inflammation, and physiological adaptation in equine athletes.