Stunning effectiveness of broiler chickens using a two-phase stunner: pulsed direct current followed by sine wave alternating current

Stunning efficiency of male and female broiler chickens was analysed in response to the two-phase Simmons step-up stunner. In Phase I, a pulsed DC of 550 Hz is applied in a shallow waterbath. This is immediately followed by Phase II, consisting of a metal plate with sine wave AC of 50 Hz. 120 male and female broiler chickens were randomly allocated to six stunning groups with 10 males and 10 females per group. In Phase I a voltage of 12 or 15 V was applied followed by 40, 50 or 60 V in Phase II. Stunning time was 10 and 5 s in Phase I and II respectively. The rms current per bird was recorded. To assess stunning efficiency the electroencephalogram (EEG) was recorded for 120 s post-stun. Simultaneously the occurrence of spontaneous eye lid blinking, breathing and wing flapping was assessed. The corneal reflex was tested every 20 s. The reduction of brain power in two frequency bands (2-30 Hz and 13-30 Hz) to less than 10% of the pre-stun level was analysed as indicator for adequate stunning. Female broilers showed a significantly lower rms stunning current as a result of higher electrical resistance. Phase II showed the biggest impact on stunning efficiency. Increasing voltage improved the stunning effect, but none of the analysed treatments induced unconsciousness in at least 90% of the animals. Voltage settings of more than 60 V AC in Phase II must therefore be applied. The majority of animals recovered from stunning in all groups. The occurrence of physical reflexes was suppressed in animals that were considered sensitive in the EEG analysis. Assessment of these reflexes for the evaluation of stunning efficiency can therefore not be recommended for this stunning method. No animal showed tonic-clonic convulsions following stunning and the level of severe wing flapping was very low in all groups. Meat quality advantages of this stunning method can therefore be expected, but this must be assessed in a separate study. It must be investigated if this effect can be maintained with higher voltage settings to ensure adequate stunning efficiency.