Effect of transdermal melatonin on circulating cortisol and blood chemistry in horses exposed to transport stress.

Effect of transdermal melatonin on circulating cortisol and blood chemistry in horses exposed to transport stress.

Overview

• This study investigated how applying melatonin through the skin affects stress markers like cortisol and blood chemistry in horses, particularly under the stress of transportation.
• Researchers tested whether melatonin could reduce physiological stress responses caused by a 3-hour trailer ride.

Study Design

• Sixteen horses were divided into four groups based on two factors: melatonin treatment (melatonin vs. no melatonin) and transport status (transported vs. non-transported).
• The four groups were:
  • Control (CON) – no melatonin, no transport
  • Transport only (TRS) – transport but no melatonin
  • Melatonin only (MEL) – melatonin but no transport
  • Melatonin plus Transport (MELTRS) – both melatonin treatment and transport
• The melatonin groups received 24 mg of transdermal melatonin daily for 21 days leading up to testing.
• On day 21, the transported groups underwent a 3-hour trailer ride to induce transport-related stress.
• After transport, blood samples were taken to measure key physiological stress indicators: cortisol, melatonin, glucose, bilirubin, sodium-to-potassium ratio, and other standard blood chemistry parameters.

Key Findings

• No significant interaction between transport status and melatonin treatment was found, meaning the effects of transport and melatonin acted independently.
• Transport had significant effects:
  • Elevated cortisol levels, which is a classic biomarker indicating stress response.
  • Increased glucose, suggesting metabolic changes related to stress.
  • Raised direct bilirubin and sodium-to-potassium ratio, indicating some changes in liver function and electrolyte balance linked to transport stress.
• Melatonin treatment significantly reduced cortisol levels across the horses, indicating a possible stress-reducing or calming effect.
• The reduction in cortisol induced by melatonin suggests transdermal melatonin might mitigate some physiological impacts of transport stress.

Implications and Future Directions

• This study provides preliminary evidence that melatonin delivered transdermally can lower cortisol and modulate stress responses in horses subjected to transportation.
• Since cortisol is a key stress hormone, reducing its elevation has potential welfare benefits for horses facing stressful situations such as traveling.
• Transport-related increases in glucose, bilirubin, and electrolyte ratios highlight the physiological toll transport can take, emphasizing the need for interventions.
• Further studies with larger sample sizes and additional physiological and behavioral parameters are needed to confirm the benefits and mechanisms of transdermal melatonin.
• Future research could also explore optimal dosing, timing, and delivery methods of melatonin to better support horse health during stress.