Métrologie de la douleur animale : 
validation sur des modèles de douleur viscérale bovine et articulaires canins

Pain is a multidimensional experience involving sensitive, emotional and cognitive components. Theoretically, there are multiple methods by which pain can be assessed including sensitive, behavioural, physiological, or neurophysiological measurements. However, little work has been done to validate these measurements in veterinary medicine. The presented research program including both Master and Doctorate works was intended to address partially this paucity of research. For this purpose, our work would validate some behavioural and physiological methods of pain assessment by contrasting pain expressions (cows and dogs) in painful animals (negative control) and animals treated with preventive analgesic or curative treatment following surgery-induced (bovine visceral and canine orthopaedic models) pain or natural occurring disease (osteoarthritis in dog). A pain study was first conducted to compare measurements of placebo treated-cows with postoperative analgesic treated-cows during 21 days following surgical induction of sustained visceral pain. Placebo treated-cows were found to have increased pain sensitization and decreased concentration of cerebrospinal fluid noradrenaline and transthyretin, less motor activity (but higher than in analgesic groups), more restlessness recorded with video-analysis and increased partially stress with measurement of electrodermal activity (EDA). This first study allowed a selection of methods of interest for pain evaluation including spinal biomarkers, measurement of sensitization, behavioural recording with video-analysis and motor activity with biotelemetry. Therefore, two canine pain experiments, with use of similar methods of pain assessment presented above, were performed to compare responses to pain between preventive analgesics treated-dogs (opioids and anti-inflammatory drug, study #2) or a bisphosphonate (tiludronate in study #3) with placebo-treated dogs. Only the pain scales were different among the projects. For project #2, analgesic treated-dogs were found to have lower pain scores measured with the so-called 4A-VET postoperative pain scale while simultaneously exhibiting reduction of EDA response up to 1 hour following trochleoplasty. In addition, the occurrence rate of the spontaneous behaviour ‘Walking with full weight bearing of the operated leg’ recorded with video-analysis, was higher in analgesic treated-dogs when compared with the placebotreated dogs at 24 hours post trochleoplasty. The pain study #3 was then conducted and demonstrated central sensitization (assessed with quantitative sensory testing and spinal biomarkers) in all control dogs at 56 days post induction of the canine osteoarthritis pain model. Nevertheless, tiludronate treated-dogs were found to have different spinal biomarkers (substance P and transthyretin), decreased peripheral sensitization, more peak vertical force (PVF), which is a kinetic gait parameter, and increased occurrence rate of ‘Walking with full weight bearing of the operated leg’. Interestingly, the central sensitization was associated negatively with PVF and positively with both EDA and ‘Walking with full weight bearing of the operated leg’. Finally, a fourth pain study was conducted to examine whether some of the methods performed validity and sensitivity in clinical condition with osteoarthritic dogs. For this purpose, osteoarthritic dogs were treated with a green-lipped mussel enriched-diet, having both anti-inflammatory and chondroprotective expected activities. The treated-dogs were found to have low pain scores measured with the pain scale for owner named CSOM, increased PVF and motor activity. Indeed, CSOM scores were associated with both PVF and motor activity. Taken together, the results suggest that video-analysis would assess pain expression through objective, predictive and unique evaluation whatever the species or the model, whereas spinal biomarkers are promising. The PVF changes were related to orthopaedic pain. Sensitization appeared to be common to the pathological pain pattern. The EDA was not validated for pain assessment in animals. Decreased motor activity is pain suggestive. Psychometric evaluation of the pain scales remained only exploratory at this (early) stage of development and knowledge of the present pain scales.

Keyphrases: Bovin, Pain, Metrology, Surgical pain, Osteoarthritis, Cattle, Dog, Pain scale, Video-analysis, Gait analysis, Sensitization