Stunning efficiency of broilers after electrical waterbath stunning with an alternating current was assessed using electroencephalograms (EEG) and physical reflexes. Four hundred eighty-nine broilers (246 males and 243 females) were stunned in an electrical waterbath with a rectangular alternating stunning current of 60, 80, 100, 120, and 150 mA and frequencies of 70, 100, 200, 400, 800, and 1,500 Hz. Stunning time was 10 s. The EEG was recorded for 120 s poststun. Occurrence of spontaneous breathing, eye blinking, and wing flapping and the corneal reflex were recorded. The EEG was analyzed regarding the occurrence of a profound suppression to less than 10% of the prestun level in the 2 to 30-Hz band and 13 to 30-Hz band. The occurrence of epileptiform patterns was assessed and the occurrence of clonic-tonic convulsions was recorded. Statistical analysis showed a highly significant effect of stunning frequency and stunning current for all groups in the EEG analysis. Stunning frequencies above 400 Hz or below 100 mA did not result in profound suppression of brain power to less than 10% of the prestun level in more than 90% of the broilers and can therefore not be recommended. More than 80% of the birds stunned with 70 or 100 Hz at 100 mA or 70, 100, and 200 Hz with 120 and 150 mA did not recover from stunning. The occurrence of epileptiform activity could only be observed in a few birds. It is assumed that this is due to the long stunning time of 10 s and epileptiform activity could have occurred just before EEG recording started. A maximum of 30% of birds with corneal reflexes and spontaneous eye blinking should not be exceeded, whereas at 15 s poststun, not more than 15% of birds should show spontaneous eye blinking. Wing flapping occurred in at least 50% of birds with adequate stunning results. This seems to be related to convulsions and could cause meat quality defects.

Stunning efficiency of a pulsed direct current was assessed regarding the effect on the electroencephalogram (EEG) and physical reflexes. Four hundred sixty-seven broilers (males and females) were stunned in an electrified waterbath with 60, 80, 100, 120, and 150 mA at frequencies of 70, 100, 200, 400, 800, and 1,500 Hz. Stunning time was 10 s. The EEG recordings lasted for 120 s poststun and simultaneously the occurrence of breathing, spontaneous eye blinking, corneal reflex, and wing flapping was recorded. The EEG records were assessed regarding a profound suppression to less than 10% of the prestun brain power in 2 brain frequency bands, 2 to 30 Hz and 13 to 30 Hz. The EEG results showed a significant effect of stunning frequency for all analyzed parameters. Stunning frequencies of 800 and 1,500 Hz did not achieve adequate stunning results. With a minimum stunning current of 120 mA at frequencies of 70 or 100 Hz or 150 mA at 200 Hz, more than 80% of the animals did not resume breathing. Currents of 80 and 100 mA at 70 or 100 Hz achieved unconsciousness in more than 90% of the birds and birds recovered within 30 to 40 s poststun. Epileptiform activity was found in a relatively low proportion of EEG traces. This could be explained by the long stunning time of 10 s, in which epileptiform activity might have occurred already before the start of EEG recording. Direct current stunning causes less cardiac arrest during stunning, but occurrence of breathing seems more related to cardiac function than to consciousness. A maximum of 30% corneal reflexes and spontaneous eye blinking seems acceptable with a maximum of 15% spontaneous blinking at 15 s poststun. Fourty percent of wing flapping occurred in all effectively stunned groups. Direct current seems to have a different effect on male and female broilers because significantly more male broilers showed reflexes, whereas simultaneously the likelihood of profound EEG suppression was higher. Further investigation of this effect is necessary.

Stunning effectiveness of male and female broiler chickens was analyzed in response to different waveforms at 3 constant voltage levels. In total, 180 male and female broiler chickens were stunned using a sine wave alternating current (AC) of 50 Hz, rectangular AC of 70 Hz, and pulsed direct current (DC) of 70 Hz (duty-cycle 1:1) with a constant voltage of 60, 80, or 120 V, respectively. In each stunning group, 10 male and 10 female birds were stunned for 4 s. The current obtained by every bird was recorded. For stunning efficiency, the electroencephalogram (EEG) and physical reflexes were recorded and analyzed. The EEG was recorded for 120 s poststun. Simultaneously, the occurrence of spontaneous eye blinking, wing flapping, and breathing was assessed, and the corneal reflex was tested every 20 s poststun. The EEG was analyzed regarding the occurrence of a profound suppression to less than 10% of the prestun level in the 2 to 30 Hz and 13 to 30 Hz bands. Female broilers obtained a significantly lower stunning current compared with that of the males. This resulted in a lower stunning efficiency for females, when the same constant voltage was applied to males and females. The waveforms required different amounts of currents to achieve a 90% stunning efficiency. A minimum necessary stunning current of 70, 90, and 130 mA could be established for sine wave AC, rectangular AC, and pulsed DC, respectively. The low stunning efficiency of pulsed DC might be caused by the short stunning time of 4 s. This effect should be further investigated for DC stunning. Very few birds stunned with AC resumed breathing following stunning, indicating stun to kill. Pulsed DC stunning showed a lower effect on the induction of death. The level of wing flapping, indicating convulsions and possible meat quality defects, was higher for the AC treatments.