Effect of season of collection and storage method on equine hair cortisol concentration.

Overview

• This study investigated how the season when horse tail hair is collected and the method used to store the hair samples affect the measured cortisol levels in the hair.
• The findings help to better understand how to use hair cortisol concentration (HCC) as a reliable indicator of chronic stress in horses.

Introduction and Background

• Cortisol is a hormone commonly measured in animals to assess stress levels.
• Serum cortisol measures acute stress but only captures stress at the moment of blood collection.
• Hair cortisol concentration (HCC) offers a way to understand chronic stress by integrating cortisol exposure over time as the hair grows.
• Monitoring HCC in horses can help caretakers identify chronic stress and modify management practices to improve animal welfare.

Research Objective

• To evaluate how the month of hair collection (season) and the storage method of hair samples influence cortisol levels detected in equine hair.

Methods

• Sample Collection:
  • Tail hair was collected from 32 mature horses.
  • Collection occurred twice in the same year: once in February (Winter) and once in August (Summer).
  • Both collections were performed at the same location to control environmental variables besides season.
• Storage Conditions:
  • Each hair sample was split into two parts.
  • One half was stored at room temperature (21.1°C) in a climate-controlled environment inside a cardboard box (referred to as ROOM storage).
  • The other half was stored frozen at -20°C (referred to as FROZEN storage).
  • February/Winter samples were stored for 8 months before analysis, August/Summer samples for 2 months.
• Measurement:
  • Hair cortisol concentration was analyzed from the stored samples.

Results

• Storage Method Impact:
  • Frozen samples had significantly higher measured cortisol concentrations than room temperature stored samples (P=0.0278).
  • This suggests freezing better preserves cortisol in hair samples over time.
• Seasonal Impact:
  • Samples collected in August/Summer showed significantly higher cortisol concentrations than those collected in February/Winter (P=0.0067).
  • This is likely due to longer daylight hours in summer, which can affect cortisol production or deposition in hair.
• Interaction Between Factors:
  • No significant interaction was found between storage method and season of collection, meaning these factors independently affected HCC.

Conclusions

• Freezing is the preferred storage method to preserve equine hair cortisol concentrations for later analysis.
• Season or month of hair collection influences cortisol levels in equine hair, with summer collection yielding higher values than winter.
• Researchers and equine managers should consider both the storage condition and season when interpreting hair cortisol measurements for stress assessments.
• This study supports the use of hair cortisol concentration as a valuable tool for monitoring chronic stress in horses over time, assisting in improving animal welfare management.