Validation of behavioural indicators used to assess unconsciousness in sheep

The validity of behavioural indicators to assess unconsciousness under different slaughter conditions is under (inter)national debate. The aim of this study was to validate eyelid-, withdrawal-, threat reflex and rhythmic breathing as indicators to assess unconsciousness in sheep. Sheep were monitored during repeated propofol anaesthesia (n = 12) and during non-stunned slaughter (n = 22). Changes in the EEG and behavioural indices of consciousness/unconsciousness were assessed and compared in sheep. Threat reflex and rhythmic breathing correlated with EEG activity during propofol anaesthesia whilst absence of non-rhythmic breathing or threat reflex indicated unconsciousness. None of the behavioural indicators correlated with EEG activity during non-stunned slaughter. Absence of regular breathing and eyelid reflex was observed 00:27 ± 00:12 min and 00:59 ± 00:17 min (mean ± SD) respectively after animals were considered unconscious, indicating that absence of regular breathing and eyelid reflex are distinctly conservative indicators of unconsciousness during non-stunned slaughter in sheep.