Hair Cortisol Concentrations in Feral Horses and the Influence of Physiological and Social Factors.
Authors: Medill Sarah A, Janz David M, McLoughlin Philip D
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Hair cortisol concentration (HCC) provides a reliable window into chronic stress physiology in horses, and this analysis of 282 samples from a feral population on Sable Island reveals patterns distinctly shaped by reproductive demands and social hierarchies. Researchers found that mares with dependent foals exhibited significantly elevated HCC compared to non-lactating females (p = 0.005), whilst poor body condition score strongly predicted higher cortisol in both sexes, suggesting that nutritional stress and the metabolic burden of reproduction represent major HPA axis activators in free-ranging animals. Social factors further influenced cortisol in mares—harem size and proximity to bachelor groups both appeared in top-ranked models—though stallions showed a simpler endocrine profile dominated by age, body condition, and year-to-year environmental variation. These findings highlight a fundamental distinction between feral and domestic horses: whereas managed animals may experience stress primarily from training, handling, or stable management, wild horses face overlapping physiological stressors from reproduction, nutrition, and complex social positioning that collectively shape their cortisol profiles. For practitioners working with performance or breeding horses, this underscores the importance of assessing body condition, reproductive status, and social stressors holistically when interpreting behavioural or performance changes, as chronic HPA activation may reflect cumulative physiological demands rather than a single identifiable cause.
Read the full abstract on PubMed
Practical Takeaways
- •Monitor nursing mares closely for elevated stress physiology; lactating females show naturally elevated cortisol that compounds other stressors
- •Body condition management is critical for stress mitigation in feral and free-roaming populations; poor condition correlates with HPA axis activation independent of other factors
- •Social structure influences stress hormone levels in horses, particularly for females; management of group composition may help reduce physiological stress
Key Findings
- •Females with dependent foals had significantly higher hair cortisol concentrations than those without foals (p = 0.005)
- •Poor body condition index correlated with elevated cortisol in both sexes (females p < 0.001, males p = 0.028)
- •Female cortisol levels were best predicted by age, body condition, presence of foal, harem size, and number of bachelor males nearby
- •Male cortisol levels were primarily influenced by age, body condition, and year of collection, with social factors playing a secondary role