Variation in salivary cortisol responses in yearling Thoroughbred racehorses during their first year of training.
Authors: Holtby Amy R, McGivney Beatrice A, Browne John A, Katz Lisa M, Murphy Keith J, Hill Emmeline W
Journal: PloS one
Summary
# Editorial Summary Yearling Thoroughbreds experience profound physiological challenges during their transition to racing training, yet individual variation in stress response to this critical period remains poorly characterised. Researchers collected salivary cortisol samples from 96 Flat racehorses at three resting timepoints and before and 30 minutes after three novel training events (first long-reining, first backing, first gallop work), measuring hormone concentrations via ELISA to assess acute stress responses. Resting cortisol levels showed no significant change across the training yard adjustment period; however, cortisol concentrations increased significantly (P<0.005) within 30 minutes of all three novel training events, with notable individual variation in the magnitude of this response. These findings suggest salivary cortisol measurement could serve as an objective, non-invasive biomarker for identifying yearlings with heightened stress reactivity to training milestones, potentially informing decisions about training progression, environmental management, and early identification of animals at risk of stress-related injury or behavioural issues during this formative phase of their racing careers.
Read the full abstract on PubMed
Practical Takeaways
- •Salivary cortisol testing may help identify yearlings with heightened stress responses to training milestones, potentially supporting early detection of horses at risk for welfare or soundness issues during early training
- •Baseline resting cortisol levels appear stable during early training, so acute cortisol spikes around specific training events are more informative than routine measurements
- •Consider that individual variation in measured stress response is normal and substantial—horses showing higher cortisol responses may benefit from modified training approaches or additional settling time rather than being classified as 'problem' horses
Key Findings
- •Salivary cortisol concentration increased significantly (P<0.005) within 30 minutes after all three novel training events (first long-reining, first backing, first gallop work) compared to baseline
- •No significant difference in resting cortisol levels was detected across three timepoints over 2-3 weeks of initial training (P>0.05)
- •Individual variation in post-event cortisol response was observed across all training milestones, indicating differences in acute physiological stress response between horses
- •Salivary cortisol measurement via ELISA can objectively assess individual stress responses to early training environments in yearling racehorses