#13-188

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Date Full Report Received

Date Abstract Report Received

Investigation

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Co-Investigators: Mhairi Sutherland, Ngaio Beausoleil, Nikki Kells

According to current commercial practice, tail docking of pigs is performed without analgesia and is therefore acutely painful. Negative public perception concerning tail docking without the use of pain-relief is increasing; therefore it would benefit the industry to investigate plausible methods of pain mitigation. Before undertaking pain mitigation studies, pain assessment techniques should be validated across the range of ages at which tail docking is routinely carried out.

The aim of the current study was to examine the electroencephalographic (EEG) responses of anaesthetised pigs aged between 1 and 15 days to the painful stimulus of tail docking, in order to identify potential differences in pain processing within this age range and to determine the suitability of EEG as a tool for pain assessment across this age range.

Ten pigs aged 1, 5, 7, 10, 12 and 15 days (n=60 total) were lightly anaesthetised and their EEG continuously recorded whilst undergoing tail docking using side cutter pliers. The summary variables median frequency (F50), 95% spectral edge frequency (F95) and total power (PTOT) were generated from the recorded EEG data. Statistical analyses were performed to compare consecutive 15-second blocks of EEG to baseline within each age group and to compare time blocks between different ages.

EEG responses typical of pain signal processing were seen in pigs aged 5–15 days, validating the use of EEG for pain assessment in this age range. There was limited evidence of an age-related progression in EEG responses to tail docking, with more pronounced responses observed with increasing age. The change in F50 varied according to age, with F50 showing either no change or a transient decrease after docking in younger pigs (1–7 days) and no change or an increase in older pigs (10–15 days), with 10 day-old pigs exhibiting an initial decrease followed by a later increase. The absence of an initial decrease in F50 in 15 day-old pigs suggests that the mature response to tail docking emerges by 15 days of age.

One day-old pigs showed no statistical evidence of a nociceptive response following tail docking, and exhibited lower EEG frequency overall than the other age groups, suggesting a difference in neural maturity and/or processing of pain signals at this age. Whether or how this relates to pain perception in conscious pigs requires further investigation. However, these data provide some support for current recommendations that tail docking be carried out within 72 hours of birth.

Based on the more pronounced and adult-like EEG responses observed in older pigs (>10 days of age), these may provide a better model for the future EEG study of general pain mitigation strategies.