The finish line is only part of the story; the real tale of an endurance horse's struggle is written in its saliva.
Scientists have discovered that saliva contains precious biological information about a horse's physiological state. Salivary cortisol, the hormone measured in these studies, represents the biologically active, unbound fraction of cortisol that can freely diffuse from blood into saliva 2 .
The crowd cheers as an endurance horse crosses the finish line, muscles gleaming and nostrils flaring. Yet the most compelling story of its performance isn't visible to the naked eye. It's hidden in the stress hormone cortisol, silently circulating in the athlete's saliva, revealing everything from its response to heat to its anxiety about competition. For researchers and veterinarians, this clear liquid has become a crystal ball into the hidden world of equine stress and performance.
This non-invasive method has revolutionized how we understand the immense pressures these equine athletes face—not just from physical exertion, but from transportation, unfamiliar environments, and even the handlers and riders they work with 2 .
Cortisol, produced by the adrenal cortex, serves as one of the primary chemical messengers indicating stress levels in horses 3 . Unlike blood collection which can itself cause stress, saliva sampling offers a non-invasive alternative that accurately reflects the biologically active hormone levels without disturbing the animal 3 8 .
In endurance competitions, which can span 40 to 160 kilometers, horses face a perfect storm of potential stressors: transportation, separation from stablemates, veterinary examinations, unfamiliar surroundings, and the physical demands of covering immense distances 2 .
Research reveals that not all horses respond equally to the challenges of endurance racing. One comprehensive study of 38 Arabian purebred horses found that mares consistently showed higher cortisol levels than their male counterparts 1 2 .
This hormonal difference may reflect varied stress responses or distinct physiological coping mechanisms between genders.
A horse's previous competition experience significantly shapes its stress response. Research comparing 40 km and 80 km races found that less experienced horses in the shorter distance category had significantly higher pre-competition eye temperatures than their more seasoned counterparts 2 .
Despite similar ages, the 40 km horses had fewer competition kilometers under their saddle, suggesting that familiarity with the competition environment helps moderate the stress response.
Endurance horses often compete under demanding environmental conditions, and research confirms these factors influence cortisol secretion. Studies document that horses running the longest distances at the highest temperatures showed the most pronounced cortisol increases 1 .
This highlights the combined stress of physical exertion and thermoregulatory challenge, helping explain why hot weather competitions pose particular risks to equine athletes.
In 2021, a comprehensive study sought to unravel the complex relationship between cortisol and performance by tracking both salivary cortisol and infrared thermography of eye temperature (IRTET) during actual endurance competitions 2 . This innovative approach allowed researchers to compare two non-invasive stress indicators simultaneously under real-world conditions.
The research team recruited 61 horses participating in both 40 km and 80 km endurance qualifier competitions. They collected saliva samples at multiple time points:
Before the competition began
After the first phase (30-40 km)
As applicable for the race distance
Saliva collection used plain cotton Salivettes—special swabs inserted into the horse's mouth and then chewed to absorb saliva 2 .
The study revealed several crucial patterns:
| Competition Stage | 40 km Race Cortisol (ng/ml) | 80 km Race Cortisol (ng/ml) | Key Findings |
|---|---|---|---|
| Pre-Inspection (Baseline) | 0.27 ± 0.36 | 0.27 ± 0.36 | No significant difference between distances |
| Vet Gate 1 (First Check) | Moderate increase | 93-256% increase | Most dramatic rise occurred in 80 km horses |
| Later Vet Gates | Modest or lower levels | Modest or lower levels | Adaptation to exercise stress |
Understanding equine stress responses requires specialized equipment and methods. The non-invasive nature of these tools has revolutionized welfare research in competitive settings.
Specialized containers with cotton wool swabs designed for saliva collection without stress 3 7 .
Commercial kits that accurately measure cortisol concentrations in saliva samples with high precision 3 4 .
Used to measure eye temperature changes that correlate with autonomic nervous system activation during stress 2 .
Programs like SAS help researchers manage complex data sets and detect subtle patterns in stress response data 3 .
The growing understanding of salivary cortisol patterns has profound implications for how we manage endurance horses. Recognizing that transportation, unfamiliar environments, and rider ability all contribute to the stress response emphasizes the need for holistic management approaches that address psychological as well as physical preparation 2 .
However, the identification of individual horses with exaggerated or prolonged stress responses could help veterinarians and trainers identify animals needing specialized preparation or potentially different career paths.
Future research may focus on individual differences in stress resilience, potentially identifying genetic markers associated with more adaptable temperaments . Such advances could eventually help match horses to appropriate careers while enabling proactive management strategies for those predisposed to heightened stress responses.
The story of salivary cortisol in endurance horses reminds us that these equine athletes face challenges that extend far beyond physical endurance. Their success depends on a complex interplay of experience, gender, environment, and individual stress resilience—all reflected in this telling hormone.
As research continues to decode the messages hidden in saliva, we move closer to competitions that respect both the physical and psychological needs of these remarkable animals. The finish line tells us who crossed first, but cortisol reveals how much it cost them to get there—and how we might make the journey easier for the next competitor.
For those interested in exploring this fascinating field further, the open-access study "Salivary cortisol and eye temperature changes during endurance competitions" in BMC Veterinary Research provides an excellent starting point for understanding the practical application of these research methods 2 .