Assessment of commercially available constant voltage head-only electrical stunning systems for turkeys

Abstract

There is limited information on the slaughter systems employed by small-scale poultry producer/processors in the UK. This study aimed to evaluate these systems through: (1) a survey of slaughter practices used by small-scale UK producer/processors; and (2) an experimental assessment of stunning effectiveness in turkeys ( Meleagris gallopavo domesticus ) using the three most commonly reported head-only electrode configurations. A survey of 20 poultry and waterfowl producer/processors revealed substantial variation in stunning equipment, electrode design and reported electrical parameters. Constant-voltage systems predominated, and many respondents were unable to report the current, voltage or frequency used. Four producer/processors reported operating below the legal minimum current for turkeys (400 mA), and a range of electrode types was identified, with the three most reported tested in the experimental study. In the experimental study, 39 ex-breeding turkeys were stunned with a commercially available constant voltage (50 Hz AC sinusoidal waveform) head-only electrical stunner using single-pin, needle-pin or three-pin electrodes. Stunning effectiveness was assessed using recorded electrical parameters, current profiles, behavioural and brainstem indicators, and time to return of visual evoked potentials (VEPs). Needle-pin and three-pin electrodes produced higher peak currents and shorter times to peak current than single-pin electrodes. VEPs were initially abolished immediately after all stuns but returned earliest with single pin (12.0 [± 2.7] s, range: 5.4–24.0 s), and needle pin electrodes (15.0 [± 2.6] s, range: 4.8–35.4 s). Return of VEPs was delayed significantly longest with three-pin electrodes (26.0 [± 2.6] s, range: 13.8–52.8 s) compared to the other electrode types. There was no significant difference between treatments in time to return of rhythmic breathing or nictitating membrane reflexes. In conclusion, these findings suggest that constant-voltage head-only stunning systems may not reliably prevent recovery before or during exsanguination, although three-pin electrodes performed better than the alternatives.