Prolonged suppression of the innate immune system in the horse following an 80 km endurance race.

This study investigates the impact of long-duration endurance exercise, specifically an 80km run, on the immune system of horses. Findings reveal a prolonged suppression of the horse’s innate immune system following such exercise, possibly contributing to an increased susceptibility to respiratory infections.

Study Objective

The primary purpose of this research was to evaluate the effects of an 80 km endurance race on a number of immune system and metabolic markers in eight endurance-trained horses. These indicators were monocyte and neutrophil oxidative burst (the anti-microbial action of immune cells), serum cortisol (stress hormone), glutamine (amino acid with immune significance), and plasma glucose concentrations.

Research Methods

• Blood samples were collected from the participating horses before and after the 80 km endurance race.
• Measurements were taken for monocyte and neutrophil oxidative burst, serum cortisol, glutamine, and plasma glucose concentrations.
• The time to complete the race was recorded, and changes in these markers were analyzed post-race.

Results of the Study

• The average completion time for the 80 km race was approximately 306 minutes.
• Immediately after the race, serum cortisol concentration, blood monocyte, and neutrophil counts were found to be higher.
• On the contrary, blood lymphocyte counts and plasma glucose concentration had decreased.
• The oxidative burst activity of neutrophils and monocytes had decreased post-race and had not returned to pre-race levels even after three days of rest.

Conclusions

Overall, the study found that prolonged exercise adversely affects the function of horses’ innate immune system, and this effect persists for several days post-race. Even though the precise causes triggering the decline in the immune system function following a prolonged bout of exercise are unclear and can be multifactorial, one contributing factor could be the rise in the serum cortisol response during such extended physical activity. Thus, consistent long-term exercise may result in an enduring suppression of the horse’s innate immune system function, potentially accounting for the reported increases in infectious episodes in horses during training.