M.A. Gerritzen

Slaughter of poultry during the epidemic of avian influenza in the Netherlands in 2003

During an outbreak of avian influenza in the Netherlands in spring 2003, the disease was controlled by destroying all the poultry on the infected farms and on all the farms within a radius of 3 km. In total, 30 million birds were killed on 1242 farms and in more than 8000 hobby flocks, by using mobile containers filled with carbon dioxide, mobile electrocution lines and by gassing whole poultry houses with carbon monoxide or carbon dioxide. Observations of these methods were used to compare their effectiveness and capacity, and their effects on the welfare of the birds. Gassing whole poultry houses had a much greater capacity than mobile equipment, and catching live birds to bring them to a mobile killing device caused extra stress and could cause pain due to injuries inflicted when catching and handling them. Gassing whole poultry houses with carbon monoxide requires strict safety regulations and, therefore, gassing with carbon dioxide was considered preferable. However, this method is not suited to all types of housing, and in these circumstances mobile killing devices were a useful alternative.

Animal welfare concerns during the use of the water bath for stunning broilers, hens, and ducks

European legislation demands that slaughter animals, including poultry, be rendered immediately unconscious and insensible until death occurs through blood loss at slaughter. This study addressed requirements for stunner settings (i.e., voltage, wave oscillation frequency) and response parameters (i.e., applied current, behavior) affecting effective water bath stunning. An inventory of current electrical stunning practice was performed in 10 slaughterhouses in the Netherlands. Thereafter, measurements were performed using a single-bird water bath to examine the effects of stunner settings based on the average technical settings observed in the slaughterhouses. Responses were recorded at 50, 400, and 1,000 Hz on broilers and hens and at 50 and 400 Hz on ducks under controlled laboratory conditions. Effects of voltage settings (broilers: 100 to 400 V; hens: 150 to 300 V; ducks: 150 to 400 V) on current levels (broilers: 45 to 444 mA; hens: 40 to 219 mA; ducks: 64 to 362 mA) and consciousness (response to pain stimulus) were recorded immediately after stunning. Brain and heart activity was monitored using electroencephalogram and electrocardiogram technology. Results show that effective stunning using the conventional water bath almost exclusively produces blood splashing in broilers. Effective stunning current levels did not differ significantly between broilers, hens, and ducks effectively stunned hens tended to require lower currents. Effective stuns at higher frequencies resulted in higher currents. Similar input voltage (V) levels (within and between bird type) resulted in significant variation (P < 0.001) in current levels (mA) required for an effective stun, indicating variability in electrical impedance between individual birds. Body weight and bird type did not affect the probability of an effective stun. Multi-bird water bath usage does not ensure effective stunning and technical adjustments can result in detrimental effects on meat quality. Future legislation should consider wave form, relationships between frequency and current allowing for individual impedance variation and effects on meat quality while safeguarding animal welfare.

Indicators used in livestock to assess unconsciousness after stunning: a review

Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.

Castration of piglets under CO2-gas anaesthesia

It has become common practice in pig fattening production systems to castrate young boar piglets without the use of anaesthesia. In this study, we examined whether or not CO2 gas is capable of inducing an acceptable anaesthetic state during which castration can be performed. The first step was to identify the most promising CO2/O2 mixture. Based on the results from this first experiment, a mixture of 70% CO2 + 30% O2 was chosen for further investigation as a potential anaesthetic during the castration of young piglets. Thereby, it was established whether the duration and depth of anaesthesia were acceptable for castration where the animal has to be insensible and unconscious. Physiological effects were assessed based on electroencephalogram (EEG) and electrocardiogram (ECG) measurements, blood gas values and behavioural responses. During the induction phase, the only typical behaviour the piglets exhibited when exposed to the 70/30 gas mixture was heavy breathing. All piglets (n = 25) lost consciousness after approximately 30 s according to the EEG. Heart rate decreased slowly during the induction phase, a serious drop occurred when piglets lost their posture. Immediately after this drop, the heart rate neared zero or showed a very irregular pattern. Shortly after loss of posture, most animals showed a few convulsions. None of the animals showed any reaction to castration in behaviour and/or on the EEG and ECG. On average, the piglets recovered within 59 s, i.e. EEG returned to its pre-induction pattern and piglets were able to regain a standing position. After 120 s, heart rate returned to pre-induction levels. In order to explore the usage range of CO2 concentration, 24 piglets were exposed to 60% CO2 + 20% O2 + 20% N2 for up to 30 s after loss of consciousness (as registered on EEG), and castrated after removal from the chamber. Sixteen of the 24 animals showed a reaction to the castration on the EEG. To establish the maximum time piglets survive in 70% CO2 + 30% O2, five piglets were placed in this mixture for 3 min. Two of them died. After that, four piglets were placed in this mixture for 2 min after unconsciousness, one died after 2 min. It was concluded from this study that it is possible to anaesthetise piglets with a mixture of 70% CO2 + 30% O2, but that there are limits to its safety in terms of CO2 concentration and duration of exposure. Before implementation for practical use, further research is essential to assess the limits of gas concentration and exposure times.

Physiological responses to low atmospheric pressure stunning and the implications for welfare

In low atmospheric pressure stunning (LAPS), poultry are rendered unconscious before slaughter by gradually reducing oxygen tension in the atmosphere to achieve a progressive anoxia. The effects of LAPS are not instantaneous, so there are legitimate welfare concerns around the experience of birds before loss of consciousness. Using self-contained telemetry logging units, high-quality continuous electroencephalogram (EEG) and electrocardiogram (EKG) recordings were obtained from 28 broiler chickens during exposure to LAPS in a commercial poultry processing plant. Application of LAPS was associated with changes in the EEG pattern in the form of increases in total power, decreases in mean frequency, and in particular, increases in slow-wave (delta) activity, indicating a gradual loss of consciousness. Increased delta wave activity was seen within 10 s of LAPS onset and consistently thereafter, peaking at 30 s into LAPS at which point the EEG signal shared characteristics with that of birds in a surgical plane of anesthesia. During LAPS, heart rate consistently decreased, with more pronounced bradycardia and arrhythmia observed after 30 s. No heart rate increases were observed in the period when the birds were potentially conscious. After an initial quiescent period, brief body movements (presumed to be ataxia/loss of posture) were seen on average at 39 s into the LAPS process. Later (after 120 s on average), artifacts related to clonic (wing flapping) and tonic (muscle spasms) convulsions were observed in the EKG recordings. Based on EEG analysis and body movement responses, a conservative estimate of time to loss of consciousness is approximately 40 s. The lack of behavioral responses indicating aversion or escape and absence of heart rate elevation in the conscious period strongly suggest that birds do not find LAPS induction distressing. Collectively, the results suggest that LAPS is a humane approach that has the potential to improve the welfare of poultry at slaughter by gradually inducing unconsciousness without distress, eliminating live shackling and ensuring every bird is adequately stunned before exansguination.

Multistage carbon dioxide gas stunning of broilers

The stunning quality of animals for slaughter remains under constant scrutiny. In response to previous research showing low stunning efficiency in poultry, the conventional water bath will be phased out in the Netherlands. Presently, the main practical alternative to water bath stunning of poultry is a 2-phased gas stunning method. Gas stunning methods are recognized by governments and animal welfare organizations across Europe. In this study, 3 sets of experiments were conducted on gas stunning methods using CO(2) in 2 phases. Two methods were examined to identify potential effects on bird behavior and investigate their practical implications: a 5-stage incremental CO(2) scheme lasting 6 min (treatment 1) and a 4-stage incremental CO(2) scheme lasting 4 min (treatment 2). The onset and duration of unconsciousness were specifically tested in experiment 2 by using 25 birds equipped with electrodes monitoring brain and heart activity. Behavioral responses were observed on 15 non-instrument-monitored birds kept in the same cages at that time. Results in all 3 sets of the experiments showed that multistage gas stunning was stable and consistent, and increases in CO(2) concentrations were rapid and reliable. Ambient temperatures and RH of the air remained within acceptable levels at all times. Induction of unconsciousness occurred below 40% CO(2) and did not significantly differ between treatments. Conscious birds were never exposed to high CO(2) concentrations (>40% CO(2)), yet some birds showed signs of distress (e.g., head shaking, wing flapping) before losing consciousness. Discomfort experienced during exposure to low (<40%) CO(2) concentrations compares favorably with the experiences of handling, tilting, and or shackling of conscious birds when using alternative stunning methods, implying that multistage gas stunning has distinct advantages for bird welfare. Compared with the multibird water bath system, this method provides an opportunity to guarantee that all birds are properly stunned. The risk of convulsions, which was higher with treatment 2, leading to possible injuries, indicates a preference for the 5-stage treatment.

Head-to-Cloaca Electrical Stunning of Broilers

This study was performed to identify the electrical current and exposure duration that would instantaneously render broiler chickens unconscious at slaughter when using a head-to-cloaca water bath stunner. The water in which the head was immersed was one electrode, and a steel-coned or cutaneous U-shaped electrode penetrating the cloaca was the other electrode. When an electrode penetrating the cloaca was used, a 640-Hz sinusoidal current induced a tonic-clonic phase on the electroencephalogram that lasted for 10 +/- 3 s and an exhaustion phase that lasted for 34 +/- 12 s. The heart rate was 375 +/- 39 beats/min before stunning. After stunning, the electrocardiogram revealed fibrillating for 429 +/- 58 s, after which the heart activity stopped. When a U-shaped electrode was placed on the skin at the cloaca, the same phenomenon was induced. A general epileptiform insult was induced when using a pulsed alternating square wave current of 33 mA (peak 60 V, 600 Hz, and a duty cycle of 50%), which lasted, on average, for 25 s (n = 25). When the broilers were bled within 14 s after stunning, they remained unconscious and the heart activity stopped after 237 +/- 103 s. We concluded from this experiment that broilers were effectively stunned with an average current of 111 mA (50 V, 640 Hz, sinusoidal alternating current) for 1 s when using a water bath in which the head of the broiler was immersed in water, with the water being one electrode and a steel electrode penetrating the cloaca or placed around it being the other electrode. Energy use could be reduced when an alternating pulsed square wave is used when the broilers are stunned, by using a current of approximately 33 mA (peak of 60 V, frequency of 600 Hz, and a 50% duty cycle).

Validation of behavioural indicators used to assess unconsciousness in sheep.

The validity of behavioural indicators to assess unconsciousness under different slaughter conditions is under (inter)national debate. The aim of this study was to validate eyelid-, withdrawal-, threat reflex and rhythmic breathing as indicators to assess unconsciousness in sheep. Sheep were monitored during repeated propofol anaesthesia (n=12) and during non-stunned slaughter (n=22). Changes in the EEG and behavioural indices of consciousness/unconsciousness were assessed and compared in sheep. Threat reflex and rhythmic breathing correlated with EEG activity during propofol anaesthesia whilst absence of non-rhythmic breathing or threat reflex indicated unconsciousness. None of the behavioural indicators correlated with EEG activity during non-stunned slaughter. Absence of regular breathing and eyelid reflex was observed 00:27±00:12 min and 00:59±00:17 min (mean±SD) respectively after animals were considered unconscious, indicating that absence of regular breathing and eyelid reflex are distinctly conservative indicators of unconsciousness during non-stunned slaughter in sheep.

Response to the Letter to the Editor on the surgical castration of piglets

pain relief. In general, anaesthesia does not provide any longterm pain relief. Mischler et al. (1994), however, report a prolonged mild antinociception after CO2-induced anaesthesia. In general, local as well as general anaesthesia should be supplemented with postoperative pain relief. It cannot be concluded from this research that CO2-anaesthesia leads to a mortality of 50%. Based on the results of Svendsen (2006), a pilot safety study was performed. In this pilot it became clear that a safe exposure to 70% CO2 and 30% O2 is time-limited; mortality was deemed unacceptable and thus experiments ended at the death of a maximum of two piglets. Further extensive studies (not published) showed that exposure with a maximum of 2 min is safe. Long-term effects of CO2 inhalation for the given time of 2 min are unlikely to occur in practice. The piglets of the presented research and extensive additional studies did not show any long-term effects; no respiratory diseases or other abnormalities were observed or reported. In conclusion, we agree that anaesthesia and thus CO2anaesthesia will account for a certain amount of stress during induction. It provides, however, an excellent anaesthetic state for a short-lasting surgical procedure such as castration. Additionally, CO2 is an anaesthesia that can be used at a farm level and can easily be integrated in common farm practice, as extensive experience in The Netherlands has shown by now. To complete the improvement of welfare, this anaesthesia should be supplemented with long-term postoperative pain relief. We acknowledge the concerns of the correspondents and thank you for the opportunity to respond to their comments.

Validation of indicators used to assess unconsciousness in veal calves at slaughter

European legislation states that after stunning regular checks should be performed to guarantee animals are unconscious between the end of the stunning process and death. When animals are killed without prior stunning these checks should be performed before the animal is released from restraint. The validity of certain indicators used to assess unconsciousness under different stunning and slaughter conditions is under debate. The aim of this study was to validate the absence of threat-, withdrawal-, corneal- and eyelid reflex as indicators to assess unconsciousness in calves subjected to different stunning and slaughter methods. Calves (201±22 kg) were randomly assigned to one of the following four treatments: (1) Captive bolt stunning followed by neck cut in an inverted position (n=25); (2) Non-stunned slaughter in an upright position (n=7); (3) Non-stunned slaughter in an inverted position (180° rotation) (n=25); (4) Non-stunned slaughter in an upright position followed by captive bolt stunning 40 s after the neck cut (n=25). Each calf was equipped with non-invasive electroencephalogram (EEG) electrodes before the slaughter procedure. All reflexes were verified once before the slaughter procedure. At the beginning of the procedure (T=0 s) calves were stunned (treatment 1) or neck cut in an upright position (treatment 2, 4) or inverted position (treatment 3). Calves of treatment 4 were captive bolt stunned 34±8 s after the neck cut. Reflexes were assessed every 20 s from T=15 s for all treatments until all reflex tests resulted in a negative response three times in a row and a flat line EEG was observed. In addition, reflexes were assessed 5 s after captive bolt stunning in calves of treatments 1 and 4. Visual assessment of changes in the amplitude and frequency of EEG traces was used to determine loss of consciousness. Timing of loss of consciousness was related to timing of loss of reflexes. After captive bolt stunning, absence of threat-, withdrawal-, corneal- and eyelid reflex indicated unconsciousness as determined by EEG recordings. After non-stunned slaughter, both threat- and withdrawal reflex were on average lost before calves were unconscious based on EEG recordings. The eyelid- and corneal reflex were on average lost after calves had lost consciousness based on EEG recordings and appeared to be distinctly conservative indicators of unconsciousness in non-stunned slaughtered calves since they were observed until 76±50 and 85±45 s (mean±SD), respectively, after EEG-based loss of consciousness.