Immune Functions Alterations Due to Racing Stress in Thoroughbred Horses.
Authors: Zandoná Meleiro Mônica Cristina, de Carvalho Hianka Jasmyne Costa, Ribeiro Rafaela Rodrigues, da Silva Mônica Duarte, Salles Gomes Cristina Massoco, Miglino Maria Angélica, de Santis Prada Irvênia Luiza
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Immune Function and Racing Stress in Thoroughbreds Racing imposes acute physiological demands on Thoroughbreds, yet the specific mechanisms by which competition stress affects immune competence remain incompletely characterised in clinical practice. Meleiro and colleagues examined blood immune markers and cortisol profiles in 30 racehorses across multiple timepoints—immediately post-race, during rest periods up to 11 days before and 3 days after racing, and during training intervals—using phagocytosis assays, oxidative burst analysis, neutrophil function testing, and lymphocyte proliferation measures. The most striking finding was a significant depression in neutrophil phagocytic capacity immediately after racing (both percentage and intensity reduced compared to rest and training periods), whilst oxidative burst capacity also decreased post-race (mean 524.2 ± 248.9, substantially lower than other timepoints), accompanied by elevated serum cortisol and increased circulating neutrophil percentages. Reassuringly, neither red blood cell apoptosis nor lymphoproliferation showed meaningful alterations across measurement periods, indicating that despite this transient immunosuppression, the horses' adaptive immune responses remained functionally intact. These findings suggest that whilst acute racing stress temporarily compromises neutrophil-mediated innate immunity—a window of vulnerability relevant to infection risk—recovery appears rapid and complete, supporting current management practices but highlighting the importance of minimising additional stressors during the immediate post-race period.
Read the full abstract on PubMed
Practical Takeaways
- •Racing causes transient but measurable immune suppression (reduced phagocytosis and oxidative burst) immediately post-race; monitor recovery protocols to support immune resilience
- •Elevated cortisol and neutrophil shifts indicate physiological stress response is working as expected, but horses maintain adaptive immunity—allow adequate rest between races for immune restoration
- •These biomarker changes are transient and reversible, suggesting structured training and recovery schedules are important for maintaining long-term immune competence in racehorses
Key Findings
- •Phagocytosis showed decreased percentage and intensity immediately after racing compared to rest and training periods
- •Oxidative burst in neutrophils decreased immediately post-race (524.2 ± 248.9) compared to other timepoints
- •Serum cortisol levels were significantly elevated immediately after racing
- •Neutrophil percentage increased immediately after racing, but adaptive immune function was not impaired