Effects of racing on lymphocyte proliferation in horses.

The research investigates how horse racing impacts lymphocyte proliferation responses in horses, finding a significant reduction in such responses and an increase in white blood cell counts up to 16 hours post-race. Elevated plasma cortisol levels were also recorded shortly after a race.

Study Design and Methods

• The study involved 11 Thoroughbred horses divided into two groups: a test group of 8 that participated in 14 races, and a control group of 3 that remained inactive.
• Races occurred in the late afternoon or evening, which allowed for the collection and analysis of venous blood samples before a race, immediately after a race, and the morning after the race (12 to 16 hours post-race).
• Key parameters measured in the morning samples were lymphocyte proliferation responses and the count of white blood cells (WBC). For all samples, researchers also measured plasma cortisol levels.

Findings

• Significant alterations in various health indicators were observed in the racing horses as compared to the control group.
• 12 to 16 hours following a race, lymphocyte proliferation responses in the racing horses were significantly reduced while WBC counts showed a considerable increase.
• Additionally, plasma cortisol concentrations in the racing horses also significantly increased 40 to 60 minutes after a race. This hormone is commonly linked with the stress response in animals.
• Conversely, there were no significant differences over time in lymphocyte proliferation responses, WBC counts, or plasma cortisol concentrations in the control group horses that did not participate in the races.

Implications and Conclusion

• The research demonstrates that horse racing results in physiological changes that affect the horse’s immune system, manifesting as a decrease in lymphocyte proliferation response and increase in WBC count. This suggests a suppression of the immune response post-race.
• While the clinical implications of these changes are unclear, the study advises horse managers to be cognizant of potential immune system effects following a race.
• Greater understanding of these shifts may help optimize horse care, manage stress, and improve recovery practices after races.