Repeatability and test-retest reliability of thermal and pressure pain threshold testing in healthy thoroughbred horses.

Overview

• This study evaluated the consistency and reliability of two types of pain threshold tests—thermal threshold (TT) and pressure pain threshold (PPT)—in healthy Thoroughbred horses.
• Researchers assessed how repeatable the measurements were within a single testing session and how reliable the test results were over time (one week apart).

Background and Purpose

• Quantitative sensory testing (QST) is a method used to assess how animals respond to painful stimuli, providing insights into nociception (pain perception).
• In horses, QST has potential clinical applications but variability in results caused by differences in body site tested, environmental factors, operator techniques, and animal behavior limits its broader use.
• The study aimed to evaluate:
• The feasibility of conducting TT and PPT tests on horses.
• Within-session repeatability, i.e., how consistent measurements are within a single session.
• Test-retest reliability, i.e., how consistent measurements are across two sessions spaced one week apart.

Methods

• Subjects:
• Eleven adult Thoroughbred horses participated (4 mares, 7 geldings).
• Median age was 6 years, and average body weight was approximately 558 kg.
• Testing Sessions:
• Each horse underwent testing twice, with sessions one week apart.
• Thermal Threshold (TT) Testing:
• Conducted at three anatomical sites: nostrils, withers (area above the shoulders), and coronary band (hoof region).
• Used a handheld contact heat probe that increased temperature at 0.6°C per second, with a maximum cut-off at 55°C for safety.
• Pressure Pain Threshold (PPT) Testing:
• Performed at three sites: temporomandibular joint (TMJ), seventh rib, and dorsal metacarpophalangeal joint (D-MCP, a joint in the forelimb).
• Used a blunt-tipped pressure algometer, with a safety cut-off of 2500 grams to prevent tissue damage.
• Data Collection:
• Three repeated measurements per site per session were taken to evaluate consistency.
• Analysis:
• Within-session repeatability was measured using the coefficient of variation (CV), indicating variability relative to the mean measurement.
• Test-retest reliability was assessed using the intraclass correlation coefficient (ICC), calculated from the average of the two closest measurements out of the three.

Key Findings

• Thermal Threshold (TT) Results:
• Showed moderate to high repeatability within the same session, with CV ranging from 8.9% to 13.6% depending on site.
• However, TT had poor test-retest reliability across the one-week interval at all anatomical sites tested, indicating results were not consistent between sessions.
• Pressure Pain Threshold (PPT) Results:
• Within-session repeatability was low (CV ranged from 34% to 57%), showing more variability during a single session.
• Test-retest reliability varied: moderate consistency was found at the D-MCP joint, fair consistency at the TMJ, and poor reliability at the seventh rib site.

Interpretation and Implications

• QST reliability in horses depends heavily on:
• The choice of anatomical testing site (some sites yield more consistent results).
• Environmental conditions during testing (temperature, noise, distractions, etc.).
• Behavioral responsiveness of horses, which may differ between individuals and sessions, affecting how they react to stimuli.
• The biological homogeneity of the test population, limiting the variability necessary to produce consistent repeatable measures.
• The findings indicate that while QST is a feasible tool for researching nociceptive responses in horses, careful consideration is needed regarding:
• Conducting multiple repeated trials to improve reliability.
• Maintaining strict control of temperature for thermal testing.
• Ensuring operator technique consistency to reduce variability.
• Further research is recommended to:
• Validate these methods in larger and more diverse horse populations.
• Assess QST reliability in horses experiencing natural or clinical pain conditions to determine clinical utility.