Objective assessment of chronic pain in donkeys using the donkey chronic pain scale (DCPS): A scale-construction study

Assessment of chronic pain is very important for monitoring and improving welfare and quality of life in donkeys. Freedom from disease and pain is one of the ‘five freedoms’ underlying animal welfare. The aim of the current study was to develop a pain scale for assessment of chronic pain in donkeys (Donkey Chronic Pain Scale; DCPS), including behavioural and facial expression-related parameters. The scale was applied to 77 donkeys (38 donkeys diagnosed with chronic health problems by means of clinical examination and additional diagnostic procedures and 39 healthy control animals). Animals were assessed twice daily for three consecutive days by two observers that were not masked to the condition of the animals but were unaware of the analgesic treatment regimens. Both composite, facial expression-based and combined DCPS pain scales showed excellent inter-observer reliability (Cronbach’s alpha = 0.98, 0.96 and 0.98 respectively; P < 0.001). Individual composite and facial expression-based pain scores and the resulting combined DCPS showed significant differences between donkeys with chronic conditions and control donkeys at all time points (P < 0.001). A DCPS cut-off of 6 showed good sensitivity and specificity (92% and 82.5% respectively) for presence of a chronic painful condition. Facial expression-related parameters separately showed low sensitivity. In conclusion, it is possible to use a composite pain scale for assessment of chronic pain in donkeys, based on behavioural and facial expression-based parameters. Further studies are needed to validate this pain scale before it can be used in veterinary practice.