Effects of waterbath stunning on the electroencephalograms and physical reflexes of broilers using a pulsed direct current

Abstract

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.