Electroencephalographic responses of anaesthetized pigs (Sus scrofa) to tail docking using clippers or cautery iron performed at 2 or 20 days of age.

Objective: To compare electroencephalographic (EEG) responses of pigs to tail docking using clippers or cautery iron, performed at 2 or 20 days of age.

Study Design: Prospective, randomised controlled experimental study.

Animals: A total of 40 Large White x Landrace entire male pigs aged 2 (n=20) or 20 (n=20) days were randomly assigned to undergo tail docking using clippers or cautery iron.

Methods: Anaesthesia was induced and maintained with halothane delivered in oxygen. Following instrumentation, end-tidal halothane concentration was stabilised at 1.0±0.05%, and EEG recording commenced. After a 5 minute baseline period, tail docking was performed and recording continued for additional 10 minutes. EEG data were subjected to Fast Fourier transformation, yielding the summary variables median frequency (F50), 95% spectral edge frequency (F95) and total power (P). Variables recorded during the baseline period were compared with those calculated at consecutive 15 second intervals following tail docking.

Results: Following tail docking, F50 decreased briefly but significantly in 2-day-olds, whereas 20-day-olds exhibited a sustained increase in F50 (p<0.05). Immediately after tail docking, F50 was overall lower in 2-day-olds than in 20-day-olds (p<0.05). F95 increased after docking in 20-day-olds docked using clippers (p<0.05) but did not change in 20-day-olds docked using cautery iron or in 2-day-olds docked using either method. Overall, F95 was lower in 2-day-olds than in 20-day-olds from 30 to 60 seconds after docking (p<0.05). P decreased after docking in 20-day-olds (p<0.05) but did not change in 2-day-olds. Overall, P was lower in 2- than in 20-day-olds during baseline and after tail docking (p<0.05).

Conclusions And Clinical Relevance: These data suggest that tail docking using clippers is more acutely painful than docking using cautery iron and that docking within the first days of birth may be less acutely painful than docking at a later age.