Development of quantitative mechanical sensory testing approaches for pain assessment in pigs

Background and Aims: Obtaining accurate and repeatable measurements of sensory thresholds in freely behaving animals presents a considerable challenge. The aim of these studies was to develop methods of quantitative sensory testing (QST) in juvenile pigs and evaluate two models of acute inflammatory pain.Methods: Two QST approaches were developed to detect allodynia and hyperalgesia; (1) von Frey filaments for mechanical force threshold testing around the tail root, and (2) noxious mechanical stimulation of the plantar surface of the foot pad. Assessment protocols were developed in three groupsof 8 juvenile pigs (7-9 weeks). Pigs were habituated to the investigators, apparatus and procedures before testing. Response thresholds and behaviours were measured before, and up to 24 h after inflamogen injection. Inflammation was induced by injection of capsaicin (10-100 μg) or carrageenan (3%) into the tail root or hind foot pad. Data analysed using GLM repeated measures ANOVA.Results: Inflamogen injection significantly (p < 0.05) reduced mechanical force thresholds in both tests and behavioural signs of mechanical allodynia and hyperalgesia were observed (tail flicking and foot withdrawal). Maximum reductions in force thresholds were measured 30 min after capsaicin and 4 hafter carrageenan injection. Conclusions: Quantification of thresholds using the two approaches reported provides reliable data. Capsaicin and carrageenan induced inflammation and hypersensitivity was measurable in pigs, and itsonset and duration was consistent with laboratory species. These approaches will be used in future studies to investigate the effects of neonatal tail-docking on nociceptive processing in pigs. Supported by BBSRC