# Water-Bath Stunning Efficiency, Welfare Indicators, and Carcass Quality in Taiwanese Red-Feathered Native Chickens

## TL;DR

This study examines how different voltages affect the effectiveness of electrical stunning and meat quality in a specific type of chicken in Taiwan.

## Contribution

The study provides breed-specific insights into electrical stunning effectiveness and welfare indicators for Taiwanese red-feathered native chickens.

## Key findings

- Higher voltages (140–160 V) increased the likelihood of unconsciousness but also caused more carcass defects.
- Corneal reflex and eye blinking are reliable indicators of unconsciousness in these chickens.
- Chickens with higher body fat were more likely to be stunned effectively at low voltages.

## Abstract

Electrical stunning is widely used to make chickens unconscious before slaughter, but previous studies have shown that differences among breeds, including growth rate and body composition, may influence electrical resistance and stunning effectiveness. Taiwanese red-feathered native chickens grow more slowly and differ from commercial broilers in body weight, abdominal fat deposition, and musculoskeletal conformation, which may influence electrical resistance and their response to stunning. In this study, we examined the effects of different voltage levels (80–160 V) applied using a direct-current water-bath stunner on unconsciousness, behavioural responses, and carcass quality in Taiwanese red-feathered chickens. Electroencephalography (EEG) recordings were used to confirm loss of consciousness and were compared with simple physical signs such as eye blinking and eye reflexes that are commonly checked in slaughterhouses. Higher voltage settings (140–160 V) resulted in a greater proportion of birds showing EEG-defined unconsciousness and suppression of corneal reflex and spontaneous eye blinking, although intermediate voltage levels did not show a strictly linear increase in stunning effectiveness. However, these higher voltages were also associated with an increased prevalence and severity of scored carcass defects, including wing haemorrhage and red wingtips. At very low electrical settings, chickens with higher body fat were more likely to be effectively stunned. These results show that electrical stunning conditions designed for commercial broilers may not always ensure good welfare in native chickens. Simple indicators such as eye blinking and eye reflexes can help workers judge unconsciousness on the slaughter line, but electrical settings must be carefully balanced to protect both animal welfare and meat quality.

Electrical water-bath stunning remains the predominant method used in commercial poultry slaughter worldwide yet its effectiveness and welfare implications may vary among breeds. Taiwanese red-feathered chickens differ from commercial broilers in growth rate and body composition, which may influence their response to electrical stunning. This study investigated the relationships between electrical stunning conditions, electroencephalographic (EEG) indicators of unconsciousness, behavioural reflexes, and carcass quality in Taiwanese red-feathered chickens. A total of 200 female chickens were subjected to direct-current water-bath stunning at 80, 100, 120, 140, or 160 V for 7 s. EEG activity and physical indicators of consciousness were assessed during the first 40 s after stunning, and carcass defects were evaluated post-mortem. Of the 200 birds initially evaluated, EEG data from 153 birds met predefined signal quality criteria and were included in the final analysis. EEG-defined unconsciousness was more frequent and lasted longer at higher voltages (140–160 V), although intermediate voltage levels (e.g., 120 V) did not follow a strictly linear trend. Corneal reflex and spontaneous eye blinking were strongly associated with EEG-based unconsciousness, supporting their use as practical on-site welfare indicators. At the lowest voltage (80 V), birds with higher abdominal fat percentages were more likely to be effectively stunned. In contrast, no statistically significant associations between abdominal fat percentage and stunning effectiveness were observed at 100–160 V. However, higher voltages were also associated with an increased prevalence and severity of carcass defects. These findings suggest that stunning conditions or commercial broilers may not ensure effective unconsciousness in Taiwanese red-feathered chickens. Corneal reflex and spontaneous eye blinking provide reliable, welfare-relevant indicators of unconsciousness under field conditions. Electrical settings must be carefully balanced to achieve effective stunning while minimising adverse welfare outcomes associated with excessive neuro-muscular responses.