Objective pain recognition and quantification in horses before and after orthopaedic surgery using pain scoring systems

Abstract

Objective recognition and quantification of pain in horses have been studied extensively in the past several decades, but there is still a desire for improvements. This study described the objective recognition and quantification of pain in horses before and after orthopaedic surgery measured with two different pain scales, the Facial Assessment of Pain (FAP) and the Composite Pain Scale (CPS). Ten patients with orthopaedic injuries that needed surgery and ten healthy pain free control horses were used (n = 20). Patients were scored before surgery, short after surgery (4 hours) and three days post-surgery in the morning, before the administration of pain medication, and in the afternoon, after the administration of pain medication. The horses were scored by two observers to determine the inter-observer reliability of the two pain scales. The observers scored the horses simultaneously, but didn’t discuss their findings. FAP scores were assessed with live and video observations and CPS scores were assessed with only live observations. Both the FAP and the CPS scored an acceptable inter-observer reliability for live observations (r = 0.74, P < 0.001 for the FAP and r = 0.91, P < 0.001 for the CPS), while a weak FAP inter-observer reliability was found with video observations (r = 0.08, P = 0.63) or between the FAP live and video observations (r = -0.09, P = 0.60). Both pain scales were able to distinguish between control horses and patients, but only the FAP was able to differentiate between patients before and after the administration of pain medication and between patients before and after the surgery. The FAP is therefore more reproducible for the objective recognition and quantification of pain in horses before and after orthopaedic surgery than the CPS. However, more patients and therefore more studies are needed to make the outcome of this study more reliable.