Mechanical nociception thresholds in lame sows: Evidence of hyperalgesia as measured by two different methods

Pain in pigs: How much does it hurt?

“…An obvious advantage of a hand-held algometer is that it can be applied to body areas, such as the flank or head, where it is impractical or difficult to attach a pressure-measuring device with a remote control, or to very particular locations, such as those required to assess periarticular pain . Nalon et al (2013) demonstrate that lame sows have increased sensitivity to a mechanical stimulus in limbs affected by lameness, an indication of hyperalgesia. Primary hyperalgesia is expected to occur in close proximity to damaged tissues or ongoing disease processes, as a result of inflammation and peripheral sensitisation, while secondary hyperalgesia is related to central sensitisation, possibly accounting for more widespread musculoskeletal pain (Treede et al, 1992).…”

“…The research findings presented by Dr. Elena Nalon and colleagues from the Ghent Veterinary School, Belgium, in a recent issue of The Veterinary Journal (Nalon et al, 2013) make a significant contribution to the field of mechanical nociceptive testing in pigs. In a thorough methodological study that included the systematic investigation of all limbs, repetition of measurements within testing sessions and over time, and the use of different testing approaches (hand-held probe vs. fixed actuator), these authors have generated baseline data on nociceptive thresholds in adult pigs.…”

“…Adult pigs are particularly challenging to work with due to their large body size and sometimes limited cooperation with human observers. In this respect, the option to work without the need for body contact, as described by Nalon et al (2013), is especially attractive. However, the authors report that training was necessary to accustom pigs to the straps and 'dummy actuators' of the fixed testing devices.…”

“…Primary hyperalgesia is expected to occur in close proximity to damaged tissues or ongoing disease processes, as a result of inflammation and peripheral sensitisation, while secondary hyperalgesia is related to central sensitisation, possibly accounting for more widespread musculoskeletal pain (Treede et al, 1992). Nalon et al (2013) do not attempt to distinguish between primary or secondary hyperalgesia; in their experiment, a fixed anatomical location was selected for assessment. It is possible that even lower mechanical nociceptive thresholds would have been identified in the lame sows if the source of pain had been identified more precisely.…”

“…Since a defined threshold of lameness was the clinical criterion chosen to differentiate between normal animals and those exhibiting pain, and in several cases lameness in a particular limb was assessed as 'doubtful', the lameness reported by Nalon et al (2013) was not quantified objectively, as would have been possible using force plate gait analysis (Thorup et al, 2007;Gré-goirie et al, 2013). Thus, although the study by Nalon et al (2013) found that the forelimbs had higher mechanical nociceptive thresholds than the hind limbs, it is possible that the reduced nociceptive thresholds observed in lame limbs reflected a higher prevalence of hind limb lameness, and not necessarily hyperalgesia, since the numbers of affected forelimbs vs. hind limbs were not reported.…”