Effects of training on resting peripheral blood and BAL-derived leucocyte function in horses.
Authors: Raidal S L, Rose R J, Love D N
Journal: Equine veterinary journal
Summary
# Editorial Summary Raidal, Rose & Love (2001) investigated how prolonged high-intensity training affects immune cell function in horses, using flow cytometry to measure phagocytosis and oxidative burst activity in both peripheral blood and bronchoalveolar lavage samples collected from eight horses across a 32-week training programme. Eight horses completed seven weeks of endurance conditioning followed by five weeks of standard high-intensity training; subsequently, four were assigned to continued moderate training (control) whilst four underwent deliberately escalated overtraining until performance declined. Notably, peripheral blood neutrophil phagocytosis initially increased during early high-intensity training but declined significantly from week 16 onwards in both groups, whilst the oxidative burst activity of pulmonary alveolar macrophages was substantially reduced by the study's end—yet surprisingly, no meaningful differences emerged between the control and overtrained groups. These findings suggest that the immune suppression observed was driven by protracted intense training itself rather than by overtraining per se, indicating that even appropriately planned training programmes may compromise innate immune function through sustained elevation of training loads. For practitioners managing athletic horses, this work highlights the importance of strategic recovery periods and monitoring for signs of immunosuppression (such as respiratory infection susceptibility) during extended high-intensity conditioning phases, as impaired neutrophil and macrophage function could compromise both health and performance despite appropriate training design.
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Practical Takeaways
- •Horses undergoing prolonged intense training show measurable suppression of immune cell function that may increase disease susceptibility; monitor health status closely during extended training programs
- •Performance reduction in heavily trained horses may reflect immunological fatigue rather than pure physical overtraining; consider immune function when evaluating training-related performance plateaus
- •Even control-group horses on standard high-intensity training showed immune cell suppression, suggesting that adequate recovery periods and monitoring are essential for any intensive training program
Key Findings
- •Peripheral blood neutrophil phagocytosis increased during initial high-intensity training then decreased from week 16 when workload increased
- •Oxidative burst activity of peripheral blood neutrophils and lymphocytes increased then decreased in response to training intensity
- •Pulmonary alveolar macrophage oxidative burst activity was reduced towards the end of the overtraining phase
- •Protracted high-intensity training rather than overtraining per se was associated with impaired leucocyte function, suggesting compromised non-specific immunity