Remote Controlled Nociceptive Threshold Testing Systems in Large Animals

Abstract

Nociceptive threshold (NT) testing is widely used for the study of pain and its alleviation. The end point is a normal behavioural response, which may be affected by restraint or unfamiliar surroundings, leading to erroneous data. Remotely controlled thermal and mechanical NT testing systems were developed to allow free movement during testing and were evaluated in cats, dogs, sheep, horses and camels. Thermal threshold (TT) testing incorporated a heater and temperature sensor held against the animal’s shaved skin. Mechanical threshold (MT) testing incorporated a pneumatic actuator attached to a limb containing a 1–2 mm radiused pin pushed against the skin. Both stimuli were driven from battery powered control units attached on the animal’s back, controlled remotely via infra-red radiation from a handheld component. Threshold reading was held automatically and displayed digitally on the unit. The system was failsafe with a safety cut-out at a preset temperature or force as appropriate. The animals accepted the equipment and behaved normally in their home environment, enabling recording of reproducible TT (38.5–49.8 °C) and MT (2.7–10.1 N); precise values depended on the species, the individual and the stimulus characteristics. Remote controlled NT threshold testing appears to be a viable refinement for pain research.

Analgesic Comparison of Flunixin Meglumine or Meloxicam for Soft-Tissue Surgery in Sheep: A Pilot Study

“…A similar phenomenon, where MNTs decreased in non-painful animals over time, has previously been described [53,54]. This may be due to animals becoming accustomed to the test and learning to respond as soon as the stimulus is applied (decreasing the resulting MNT) or animals simply becoming agitated and restless at repeated testing and restraint [53,54]. In this study, the lower MNTs of CON sheep at the 6 and 30 h time points were likely a result of the latter.…”

“…At 6 and 30 h post-procedure, MEL and FLU sheep did not have MNTs significantly different than CON sheep; however, this appears to be a result of CON sheep having lower MNTs at those time points than MEL and FLU sheep having higher MNTs. A similar phenomenon, where MNTs decreased in non-painful animals over time, has previously been described [ 53 , 54 ]. This may be due to animals becoming accustomed to the test and learning to respond as soon as the stimulus is applied (decreasing the resulting MNT) or animals simply becoming agitated and restless at repeated testing and restraint [ 53 , 54 ].…”

The Neuroimmune Interface and Chronic Pain Through the Lens of Production Animals

“…Quantitative sensory testing (QST) is commonly used in pain research and involves testing an animal’s response to a ramped mechanical, thermal, or electrical stimulus and recording the intensity of the stimulus applied ( Johnson, 2016 ; Taylor, 2020 ). Quantitative sensory testing is useful for assessing the development of hyperalgesia and allodynia in response to a noxious stimulus, and it is also used to investigate resolution or reduction in nociceptive thresholds over time or with interventions, such as analgesic agents.…”

“…This involves minimizing distractions such as noise and unfamiliar smells, animals or people, allowing subjects time to acclimatize to their environment, and maintaining a regular ambient temperature ( Johnson, 2016 ). Distraction or external threat, particularly in prey animals, can alter response to stimuli; generally leading to reduced focal pain sensitivity which equates to increased nociceptive thresholds ( Johnson, 2016 ; Taylor, 2020 ). When testing livestock, it is often necessary to restrain them in unfamiliar environments and it is usually not economically feasible or ethical to manage them in stringently controlled research environments, as is possible with rodents.…”

Refinements to Animal Models for Biomedical Research

“…The greatest challenge in providing analgesia for animals is pain assessment and, within this book, the utility of pain assessment strategies is also discussed. The use of nociceptive threshold testing in multiple species is described [ 13 ] along with the value of facial grimace scales [ 14 , 15 ]. In addition, the quest for an optimal approach to pain assessment in neonatal piglets, in the context of castration, is described [ 8 ].…”