Overnight dexamethasone suppression and cortisol index tests in clinically healthy horses and with crib-biting.
Authors: Osorio-Cardona J J, Usuga-Moreno V M, Martínez-Aranzales J R
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Crib-biting and windsucking are behaviourally problematic stereotypies in horses, potentially linked to hypothalamic-pituitary-adrenal (HPA) axis dysfunction, yet diagnostic tools to confirm stress-related pathophysiology remain limited. Osorio-Cardona and colleagues investigated whether the overnight dexamethasone suppression test (DST) and cortisol index—both measures of HPA axis responsiveness—could differentiate clinically healthy crib-biting horses from non-crib-biting controls in a population of 20 Colombian Creole horses maintained under identical stabling conditions. Morning and afternoon blood samples were collected to calculate the cortisol index (circadian rhythm indicator), followed by dexamethasone administration in the afternoon with subsequent cortisol measurement; serum cortisol was quantified via sandwich ELISA. Basal cortisol concentrations proved virtually identical between crib-biting (9.52 ± 7.01 µg/dl) and control horses (8.4 ± 5.30 µg/dl), neither group showed meaningful differences in cortisol index, and all animals—regardless of stereotypic behaviour—demonstrated suppression following dexamethasone. These negative findings suggest that routine DST and circadian cortisol assessment lack diagnostic sensitivity for crib-biting; practitioners should recognise the HPA axis involvement in stereotypies as multifactorial and highly variable, necessitating more sophisticated longitudinal protocols that incorporate ACTH and corticotropin-releasing hormone measurement alongside cortisol, alongside established breed-specific and individual reference ranges, before these tests can meaningfully inform clinical decision-making around behavioural cases.
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Practical Takeaways
- •Dexamethasone suppression testing and cortisol index alone cannot be used to diagnose or characterise the stress response in crib-biting horses—additional hormonal markers (ACTH, CRH) are needed
- •Crib-biting may not result in measurably elevated circulating cortisol using standard HPA axis tests, suggesting the condition's aetiology involves other neuroendocrine or behavioural pathways
- •Clinicians should not rely on single-point cortisol assays or DST as diagnostic tools for stereotypic behaviours; longitudinal sampling and species-specific reference ranges are essential
Key Findings
- •Serum cortisol concentrations were similar between crib-biting horses (9.52 ± 7.01 µg/dl) and healthy controls (8.4 ± 5.30 µg/dl)
- •Cortisol index showed no difference between crib-biting and non-crib-biting groups
- •Dexamethasone suppression test was positive in all animals regardless of clinical condition
- •DST and cortisol index failed to distinguish horses with crib-biting from clinically healthy horses