title: Mechanical nociceptive thresholds using four probe configurations in horses.
abstract: OBJECTIVE
  To examine the relationship between probe tip size and force readings of mechanical nociceptive thresholds (MTs) to identify appropriate probes for horses.
  
  
  METHODS
  Randomized, crossover study.
  
  
  METHODS
  Eight adult, mixed-breed horses aged 5-10 years, weighing 268-460 kg.
  
  
  METHODS
  Four probe configurations (PCs) were used in random sequence: 1.0 mm diameter (SHARP); 3.2 mm (BLUNT); spring-mounted 1.0 mm (SPRING), and 3 × 2.5 mm (3PIN). A remote-controlled unit on the horse increased force (1.2 N second(-1)) in a pneumatic actuator on the metacarpus. Mean MT for each PC was calculated from 10 readings for each horse. Data were log-transformed for analysis using mixed-effects anova/linear regression (p < 0.05). Variability of data for each PC was assessed using the coefficient of variation (CV).
  
  
  RESULTS
  Mean ± standard deviation MTs were: SHARP, 5.6 ± 2.3 N; BLUNT, 11.4 ± 3.4 N; 3PIN, 9.6 ± 4.6 N, and SPRING 6.4 ± 1.8 N. Mean MT for SHARP was significantly lower than for BLUNT (p < 0.001) and 3PIN (p < 0.001), but not different from SPRING (p > 0.05). Mean MT was significantly higher for BLUNT than for 3PIN (p < 0.05) and SPRING (p < 0.001). Mean MT for 3PIN was significantly higher than for SPRING (p < 0.001). Larger contact area PCs produced higher MTs than smaller PCs, but the relationship was not linear. BLUNT (area: 10-fold greater) gave a MT two-fold higher than SHARP. 3PIN (area: 20-fold greater) produced more variable MTs, less than two-fold higher than SHARP. SPRING was similar to SHARP. CVs were: SHARP, 22.9%; BLUNT, 72.3%; 3PIN, 44.2%, and SPRING, 28.7%.
  
  
  CONCLUSIONS
  The PC has nonlinear effects on MT. Therefore, it is important to define PC when measuring MT. Smaller probe tips may be preferable as MT data are less variable.
authors.affiliation: Topcat Metrology Ltd, Ely, UK.
authors.forename: Polly M
authors.initials: PM
authors.lastname: Taylor
authors.affiliation: Department of Veterinary Surgery and Anesthesiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
authors.forename: Nadia
authors.initials: N
authors.lastname: Crosignani
authors.affiliation: Department of Veterinary Surgery and Anesthesiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
authors.forename: Carlize
authors.initials: C
authors.lastname: Lopes
authors.affiliation: Department of Veterinary Surgery and Anesthesiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
authors.forename: Ademir C
authors.initials: AC
authors.lastname: Rosa
authors.affiliation: Department of Veterinary Surgery and Anesthesiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
authors.forename: Stelio P L
authors.initials: SP
authors.lastname: Luna
authors.affiliation: Department of Veterinary Surgery and Anesthesiology, Faculty of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
authors.forename: José N P
authors.initials: JN
authors.lastname: Puoli Filho
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D018592:Cross-Over Studies; D006736:Horses / Q000502:physiology* / Q000601:surgery; D008297:Male; D059225:Nociception; D010147:Pain Measurement / Q000662:veterinary; D010149:Postoperative Pain / Q000662:veterinary*
keywords: force; nociception; pain; pressure; probe size; stimulus intensity