Effect of transdermal melatonin on circulating cortisol and blood chemistry in horses exposed to transport stress.
Authors: Crossland W L, Aviles-Rosa E O, Perry E B, Crowell C, Webberson E, Brown J, Fassbender J
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Transport stress remains a significant challenge in equine practice, triggering measurable physiological responses including elevated cortisol and glucose dysregulation; this study investigated whether transdermal melatonin supplementation could attenuate these stress biomarkers in horses subjected to a standardised 3-hour trailer journey. Sixteen horses received either 24 mg/day melatonin transdermally or placebo for 21 days, with half of each group transported and half remaining stationary, allowing researchers to isolate the independent effects of supplementation and transport stress on day 21 blood chemistry and stress hormones. Transport alone significantly elevated cortisol, glucose, direct bilirubin, and sodium-to-potassium ratios, confirming transport as a potent physiological stressor; importantly, melatonin treatment produced a significant reduction in circulating cortisol levels (P = 0.029), suggesting the hormone may buffer the stress response independently of transport status. Whilst the authors found no interaction between melatonin and transport (meaning melatonin did not specifically prevent transport-induced changes), the cortisol-lowering effect has practical implications for pre-journey supplementation protocols and may warrant incorporation into stress management strategies for competition horses, breeding stock, or those with documented transport anxiety. Further research evaluating longer supplementation periods, alternative dosing schedules, and clinical outcomes such as behaviour and feed intake would strengthen the evidence base for transdermal melatonin as a stress-mitigation tool in equine practice.
Read the full abstract on PubMed
Practical Takeaways
- •Transdermal melatonin supplementation appears effective at reducing cortisol levels in horses, suggesting potential value for managing transport-related stress
- •Transport causes measurable metabolic and electrolyte disturbances in horses; melatonin may help minimize these changes
- •Consider melatonin supplementation (24 mg/day transdermal) for 21 days prior to long-distance transport in performance or competition horses, though larger studies are needed to confirm optimal dosing and protocols
Key Findings
- •Transport significantly elevated cortisol, glucose, direct bilirubin, and sodium-to-potassium ratios (P ≤ 0.039)
- •Transdermal melatonin (24 mg/day for 21 days) significantly reduced cortisol levels (P = 0.029)
- •No significant interaction between transport and melatonin treatment was observed
- •Transdermal melatonin may mitigate transport-induced physiological stress in horses