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Pain is a perceptional phenomenon built from information gathered by specialised sensory receptors for tissue damage, modified by ascending and descending spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with a negative emotional valence in the brain. Based on knowledge about porcine neuroanatomy, physiology and studies focusing on pig behaviour and pathology, as well as biomedical studies of humans and rodent models, this chapter reviews evidence for causes of pain in pigs and the possibility for quantification of indicators of pain states. The list of suggested porcine indicators of pain is split according to: (1) model studies, where tissue damage is induced experimentally; (2) pain evoked by tissue damaging procedures common to modern pig production; or (3) naturally occurring diseases or injuries. Knowing that throughout the world, human consumption of pork exceeds all other meat products, combined with the fact that the pig is considered an advantageous animal model for various human conditions, and is used extensively in biomedical research, the current low level of knowledge about porcine pain may seem paradoxical and calls for future, targeted research effort in order to be able to protect pigs from the detrimental welfare consequences of this negative affective state.

Tail docking in pigs has the potential for evoking short- as well as long-term physiological and behavioural changes indicative of pain. Nonetheless, the existing scientific literature has thus far provided somewhat inconsistent data on the intensity and the duration of pain based on varying assessment methodologies and different post-procedural observation times. In this report we describe three response stages (immediate, short- and long-term) through the application of vocalisation, behavioural and nociceptive assessments in order to identify changes indicative of potential pain experienced by the piglets. Furthermore, we evaluated the following procedural differences: (1) cautery vs. non-cautery docking; (2) length of tail removal. Sound parameters showed a significantly greater call energy and intensity exhibited by docked vs. sham-docked piglets (P0.05). Observations of general activity of the animals in a test situation failed to detect a difference among treatments (P0.05) up to 48h post-tail docking. Similarly, no difference in mechanical nociceptive thresholds indicative of long term pain was observed at 17weeks following neonatal tail docking (P0.05). The present results highlight the potential for the use of measures of vocalisation to detect peri-procedural changes possibly associated with evoked pain. Nonetheless, activity and nociceptive measures failed to identify post-docking anomalies, suggesting that alternative methodologies need to be implemented to clarify whether tail docking is associated with short- and long-term changes attributable to pain experienced by the piglets.

Topical capsaicin is a well-established model of experimental hyperalgesia. Its application to the study of animals has been limited to few species. The effect of topical capsaicin on hyperalgesia in porcine skin was evaluated as part of a study of inflammatory pain in the pig. Two experiments were carried out on pigs of 27 ± 5 kg (n = 8) and 57 ± 3 kg (n = 16). Thermal and mechanical noxious stimuli were provided (CO2 laser and Pressure Application Measurement device) to assess avoidance behaviours. Capsaicin induced significant thermal hyperalgesia in the smaller pigs (P

ObjectiveTo investigate the effects of habituation and isolation on mechanical nociceptive thresholds in pigs at the pelvic limbs and at the tail.Study designProspective randomized multifactorial study.AnimalsThirty-two healthy castrated male (experiment 1), and 12 castrated male and 12 female (experiment 2) Danish Landrace × Yorkshire pigs, weighing 63.5 ± 0.8 kg and 55.4 ± 0.6 kg (the mean ± SD, experiment 1 and 2, respectively).MethodsMechanical nociceptive thresholds were quantified with a von Frey anesthesiometer applied to two distinct anatomical regions (tail and pelvic limbs). Pigs receiving the mechanical challenge in the pelvic limbs were tested inside a cage, whereas pigs exposed to stimuli at the tail region were tested in an open arena. For both experiments, the effect of familiarity to the procedure was evaluated by comparing thresholds of nociception in habituated versus naïve pigs. The presence of a companion animal was also evaluated in pigs receiving stimuli at the pelvic limbs.ResultsPigs tested inside the cage were affected by the habituation to the procedure as indicated by the increase in willingness and time spent by the animals in the test cage. This effect was reflected in the lower mechanical nociceptive thresholds (medians with 25–75 percentiles) recorded for familiar pigs compared with naïve animals [495 g (302–675) versus 745 g (479–1000), respectively; p = 0.026]. Mechanical nociceptive thresholds measured at the tail of the pigs in the open arena were not affected by the familiarity of the animals with the experimental procedure.Conclusions and clinical relevanceThe current results reiterate the value of habituation in research involving animal behaviour. Further characterization of the methodology is needed to allow its application in the evaluation of clinical conditions in pigs.

Background and aim Cutaneous inflammation induced by ultraviolet B-light (UV-B) is considered a valuable translational pain model. Until now, the development of primary hyperalgesia has been assessed predominantly in rodents, whereas porcine skin might be advantageous due to its greater homology with human skin. The aim of the present study was to investigate porcine behavioural responses to nociceptive mechanical and thermal stimulations following UV-B inflammation. Methods One skin area of 4 cm2 in the flank of 16 male pigs of 55 ± 6 kg was irradiated by UV-B using 3xMED (Minimum Erythema Dose). Changes in pain sensitivity were assessed 24 and 48 h following irradiation via delivery of mechanical (Pressure Application Measurement device) and thermal (CO2 laser) stimulations to the inflamed skin area and to an untreated control site. Results All animals showed higher sensitivity in the inflamed skin site 24 and 48 h following irradiation, compared to the control site (P< 0.05). Pressure withdrawal threshold decreased in the inflamed site: 231 g (148–451) against 408g (347–684) after 24 hours and 200 g (106–293) against 656g (405–902) after 48 h. Similarly, latency to respond to the laser stimulus was lower at the inflamed site: 5 s (3–7) against 9 s (4–2) after 24h and 4 s (3–15) against 20 s (8–25) after 48 h. One and two days after irradiation, a tendency was found for an increased cutaneous mechanical pain sensitivity compared to baseline values in the site irradiated with UV-B light (P = 0.092). Thermal sensitivity was increased within the inflamed site 24 h after irradiation with latency changing from 17s (4–25) at baseline to 5 s (3–7) at 24 h (P =0.001). At 48 h, the response latency had not decreased any further (P = 0.414). Conclusions Our study shows that behavioural recordings are a valid tool for the assessment of mechanical and heat sensitization following UV-B inflammation in porcine skin.

Background Volatile anesthetics such as isoflurane are widely used in clinical and research contexts. Concerns have been raised that the effects of these drugs on the central nervous system may result in long-term impairment after surgery or general anesthesia. Hence, this study aimed to detect how different isoflurane concentrations influence spatial learning and cell death in adult mice. Methods Fifty-two C57BL/6 mice were randomly divided in four groups. Mice in three groups were exposed to different concentrations of isoflurane (1, 1.5, and 2%) for 1 h; the control group was not exposed to anesthesia. Five mice per group were killed 3 h after anesthesia to perform histopathologic and immunohistochemical analyses (hematoxylin-eosin staining; caspase-3 activation). Eight mice per group were used for behavioral tests (open field, T-maze spontaneous alternation, and water maze) on subsequent days. Results There were no differences between groups in the T-maze spontaneous alternation test or in the open field (no confounding effects of stress or locomotion). The group anesthetized with 1% isoflurane performed worse in the water maze task on day 1 (550.4 ±162.78 cm) compared with the control group (400.1 ± 112.88 cm), 1.5% isoflurane (351.9 ± 150.67 cm), and 2% isoflurane (364.5 ± 113.70 cm; P ≤ 0.05) and on day 3 (305.0 ± 81.75 cm) compared with control group (175.13 ± 77.00 cm) and 2% isoflurane (204.11 ± 85.75 cm; P ≤ 0.038). In the pyramidal cell layer of the region cornu ammonis 1 of the hippocampus, 1% isoflurane showed a tendency to cause more neurodegeneration (apoptosis) (61.4 ± 26.40, profiles/mm) than the group with 2% of isoflurane (20.6 ± 17.77, profiles/mm; P = 0.051). Conclusion Low isoflurane concentration (1%) caused spatial learning impairment and more neurodegeneration compared with higher isoflurane concentrations. Results for mice receiving the latter concentrations were similar to those of control mice.

Background and aim Tail docking has been suggested as an animal model of neuropathy and pain based on findings of relations between the degree of neuroma formation and the docking length. We examined effects of docking length on behaviour of piglets during and 6 h after tail docking. Methods Piglets were tail docked 2–4 d post-partum. We used 53 piglets and four treatments: intact (I), removal of either 25 (Q), 50 (H) or 75% (T) of the tail. The piglets were kept with sow and littermates under production conditions, and docked using a gas-heated instrument. Behaviour was observed during docking and for the following 6 h. Results Tail docking led to behavioural changes, the magnitude of which to some extend depended on docking length. Increased docking length led to increased intra-procedural vocalization score (0, 0.6 ± 0.2, 1.4 ± 0.2 and 1.4 ± 0.2 for I, Q, H and T, respectively, PPPP< 0.05). Pain specific behaviours such as trembling or tail flicking were registered and occurred in 5 ± 1% and 9 ± 1% of observations. However, no effects of docking length could be shown. Conclusions Piglets responded behaviourally to tail docking. Increasing docking length led to increased pain responses such as intra-procedural vocalizations, hiding behaviour and reduced rest, indicative of increased pain. These results confirm earlier reports suggesting that tail docking might be suitable as an animal model for neuropathy and pain.