Objective assessment of chronic pain in donkeys using the Donkey Chronic Pain Scale

Objective: To clinically evaluate previously developed pain scales [Donkey Chronic Pain Composite Pain Scale (DCP-CPS), Donkey Chronic Pain Facial Assessment of Pain (DCP-FAP) and combined Donkey Chronic Pain Scale (DCPS)], including behavioural and facial expression–based variables, for the assessment of chronic pain in donkeys. Study design: Prospective, blinded clinical study. Animal: A group of 77 donkeys (34 patients and 43 healthy control animals). Methods: Animals were assessed by two observers that were blinded to the condition of the animals. Results: Both DCP-CPS and DCP-FAP, and resulting combined DCPS scores, showed good interobserver reliability [intraclass correlation coefficient (ICC) = 0.91, 95% confidence interval (CI) = 0.86–0.95, p < 0.001; ICC = 0.71, CI = 0.50–0.83, p < 0.001 and ICC = 0.84, CI = 0.72–0.91, p < 0.001, respectively]. All scores (DCP-CPS, DCP-FAP and the resulting combined DCPS) were significantly higher for patients than for controls at all time points (p < 0.001 for all three scales). Sensitivity and specificity for identification of pain (cut-off value >3) was 73.0% and 65.1% for DCP-CPS, and 60.9% and 83.3% for DCP-FAP, respectively. For the combined DCPS, sensitivity was 87.0% and specificity 90.9% (cut-off value >6). Conclusions and clinical relevance: Based on behavioural and facial expression–based variables, DCPS proved a promising and reproducible tool to assess different types of chronic pain in donkeys. The combination of behavioural and facial expression–based variables showed the best discriminatory characteristics in the current study. Further studies are needed for refinement of these tools.