Factors affecting mechanical (nociceptive) thresholds in piglets

Abstract

ObjectiveTo evaluate the stability and repeatability of measures of mechanical (nociceptive) thresholds in piglets and to examine potentially confounding factors when using a hand held algometer.Study designDescriptive, prospective cohort.AnimalsForty-four piglets from four litters, weighing 4.6 ± 1.0 kg (mean ± SD) at 2 weeks of age.MethodsMechanical thresholds were measured twice on each of 2 days during the first and second week of life. Data were analyzed using a repeated measures design to test the effects of behavior prior to testing, sex, week, day within week, and repetition within day. The effect of body weight and the interaction between piglet weight and behaviour were also tested. Piglet was entered into the model as a random effect as an additional test of repeatability. The effect of repeated testing was used to test the stability of measures. Pearson correlations between repeated measures were used to test the repeatability of measures. Variance component analysis was used to describe the variability in the data.ResultsVariance component analysis indicated that piglet explained only 17% of the variance in the data. All variables in the model (behaviour prior to testing, sex, week, day within week, repetition within day, body weight, the interaction between body weight and behaviour, piglet identity) except sex had a significant effect (p < 0.04 for all). Correlations between repeated measures increased from the first to the second week.Conclusions and Clinical relevanceRepeatability was acceptable only during the second week of testing and measures changed with repeated testing and increased with increasing piglet weight, indicating that time (age) and animal body weight should be taken into account when measuring mechanical (nociceptive) thresholds in piglets. Mechanical (nociceptive) thresholds can be used both for testing the efficacy of anaesthetics and analgesics, and for assessing hyperalgesia in chronic pain states in research and clinical settings.

A Review of Pain Assessment in Pigs

“…The assessment of nociceptive responses in pigs has received recent interest because their high homology with humans provides a translational model of induced cutaneous inflammatory pain. Methods for measuring thermal and mechanical nociceptive responses in awake pigs have been described, along with factors that may influence response thresholds (139–141). Models of cutaneous inflammatory pain, using capsaicin and UV-B irradiation have been used, demonstrating thermal and mechanical hyperalgesia in pigs (142, 143).…”

Pain assessment in animal models: do we need further studies?

“…Haga et al analyzed EEG, mean arterial blood pressure, and pulse rates as indicators of pain in post-castration piglets. The results showed significant differences between animals which had received intrafunicular or intratesticular lidocaine and the control group which had not received it 86. Rukwied et al analyzed axon reflex vasodilatation by laser Doppler imaging as an indirect sign of C-fiber activation after irradiating pig skin to create erythema and applying mechanical (with von Frey needles) and thermal stimuli (with increased skin temperature to 45°C or 47°C) 87.…”

Factors affecting mechanical nociceptive thresholds in healthy sows

“…), the age and weight of the animals (Janczak et al. ; Di Giminiani et al. ), anatomical location (Di Giminiani et al.…”