An evaluation of the effectiveness of handheld stunners for stunning chickens

Two experiments were conducted in which the spontaneous physical behaviour, spontaneous electroencephalogram (EEG) and somatosensory evoked potentials were examined in chickens stunned with a handheld, head-only stunner operating at 117 v. Thirteen of 14 birds lost their evoked potentials after stunning, and when they were exsanguinated within 15 seconds they did not regain them before they died. The remaining bird appeared to have evoked potentials after stunning but there was a movement artifact in its EEG and it is possible that they were not genuine responses. When head-only stunning was applied to 50 birds for one second the birds appeared to be stunned instantaneously, in terms of their spontaneous physical behaviour. However, they recovered more rapidly than 40 birds which were stunned for seven seconds. It was concluded that the handheld stunner can stun a bird effectively, and provided that the bird's neck is cut promptly, can kill it humanely.     

Electrocorticogram spectral analysis and somatosensory evoked potentials as tools to assess electrical stunning efficiency in ducks

1. Fast Fourier transformations (FFTs) of electrocorticogram (ECoG) signals and averaging of somatosensory evoked potentials (SEPs) were used for assessing the impact of electrical stunning of ducks in a waterbath set to deliver a constant current of 150 mA, 600 Hz alternating current (AC) for 4 s. The effectiveness of stunning was determined on the basis of induction of epileptiform activity in the ECoG followed by a decrease in total power content to less than 10% of pre-stun values and abolition of SEPs. 2. One out of 10 birds was killed by the stun. FFT analysis of the ECoG signals of the remaining 9 birds showed that only one bird had a decrease of the total power to less than 10% of the pre-stun values for up to 70 s post-stun. The SEPs were retained in 6 out of 9 ducks and and 4 of them retained the evoked responses throughout the post-stun period. In the two birds showing abolition of SEPs, this was associated with a decrease in the total power content to below 10% of the pre-stun value. 3. The present experiment confirmed that the abolition of SEPs and the decrease of the total power below 10% of the pre-stun value for assessing unconsciousness after an electrical stunning in various species are also applicable to ducks. Based on this, it is concluded that electrical waterbath stunning of ducks using 150 mA of 600 Hz AC is ineffective.     

Effect of current frequency during electrical stunning in a water bath on somatosensory evoked responses in turkey's brain

Somatosensory evoked responses (SEP) in a turkey's brain were determined after water-bath stunning with a 150-mA (constant current) delivered with 50, 300 or 600 Hz, or with 75 mA, delivered with 50-Hz alternating current (AC) in order to evaluate the effectiveness of stunning. Ninety-four BUT 9 turkey hens 12 weeks of age were surgically implanted with EEG recording and left wing nerve stimulating electrodes 4 hours before stunning. They were individually stunned by immersion of the head and upper part of the neck in a water bath for 4 s. Using a 150-mA current, all birds stunned at 50 Hz showed cardiac arrest and a flat EEG immediately after the stun with no SEP recovery. The incidence of cardiac arrest at stunning decreased with increasing current frequency but SEP were lost in all birds. In birds that survived the stun, the duration of SEP abolition was on average 69 and 34 seconds at 300 and 600 Hz, respectively. Stunning with a 75-mA AC, delivered with 50 Hz, induced cardiac arrest in 32 per cent of turkeys. SEP were abolished in only 71 per cent of the birds that survived the stun, with an average duration of SEP of 66 seconds. The results indicate that increasing the frequency of a 150-mA AC current leads to a decreased stunning efficiency. A current of 75 mA per bird is unacceptable since 29 per cent of the birds do not show SEP abolition.     

Effect of electrical stunning on somatosensory evoked potentials in chickens

The spontaneous EEG and somatosensory evoked potentials (SEPs) were examined in chickens before and after electrical stunning using a waterbath stunner. Fifty-four per cent of the birds became epileptic and lost their SEPs, and 17% were non-epileptic and appeared to retain their SEPs. It was concluded that there was a reasonably close association between the presence of epileptiform activity in the EEG and the absence of SEPs following electrical stunning, but that the absence of SEPs could be preferred as an indicator of an effective stun on conceptual grounds.     

Effect of electrical stun/kill method, interval between killing and neck cutting and blood vessels cut on blood loss and meat quality in broilers

1. Broiler chickens were killed using either an electrical waterbath (WB system) delivering 120 mA per bird (50 Hz, alternating current, AC) for 4 s or an alternative stun/kill method (ASK system); where head-only stunning for 1 s was immediately followed by head-to-body (vent) application for 1 s (150 mA, 50 Hz sine wave AC). Within each stun/kill system, the neck was cut ventrally or unilaterally 20, 60, or 180 s after killing. In addition, a control group of broilers was stunned with 100 mA per bird in a waterbath using 1500 Hz AC for 4 s and were bled by a ventral neck cut within 20 s. 2. Blood leaving the neck cut was collected for 90 s in a bin placed on an electronic balance and blood loss (g/kg body weight) calculated. 3. Individually identified, unplucked and uneviscerated carcases were held at ambient temperature until the end of the experimental day and then stored overnight in an air chiller (5 degrees C). The carcases were dissected and the incidence of broken furculum and coracoid bones, haemorrhaging in P. minor and P. major muscles, and discolouration of P. major muscles were determined. 4. When neck cutting was performed in broilers 20 s after the stun or kill, the ASK and WB systems, in comparison with high frequency stunning, produced on average about 10 g per kg less bleed out. Within the stun/kill systems, broilers killed by ASK had a greater bleed out than in the WB system. Neck cutting at 20 s or 60 s post-kill resulted in a greater bleed out than when performed after a delay of 180 s. Ventral or unilateral neck cutting resulted in a similar bleed out. 5. Stunning broilers with 1500 Hz AC resulted in lower incidences of broken bones, haemorrhaging in breast muscles and muscle discolouration post mortem than the stun/kill systems. These defects were significantly lower in the ASK than in the WB system. Delayed neck cutting increased the severity of discolouration occurring Post mortem in the breast muscles. 6. It is suggested that broilers killed by ASK can be neck cut with a delay of up to 180 s without compromising bleed out. The incidence of broken bones and haemorrhaging in breast muscles are significantly less with ASK than WB. 7. Owing to the commercial benefits and potential for improved welfare at slaughter, ASK would appear to be a better method than WB.     

Effect of incomplete immersion of the head in waterbath stunners on the effectiveness of electrical stunning in ducks.

Ten ducks were subjected to electrical stunning with their heads completely immersed in the water of a waterbath, and 10 ducks received the same current while only the bill and skin over the crop made contact with the water. The effect on visual evoked responses in the brain was examined. A higher proportion of birds had lost their visual evoked responses immediately following the current with whole head immersion. It is suggested that crop and bill immersion is less effective in disturbing brain function than whole head immersion.     

Effect of wetting a chicken's feathers on the effectiveness of electrical stunning.

Chickens were electrically stunned either when their bodies and feathers were wet or when they were dry. The time to recovery of muscular activity following stunning with 81 mA was assessed, and it was found that it was quicker in the wet birds. When hens which had previously been implanted with electroencephalogram electrodes were stunned with 119 mA it was found that the prevalence of somatosensory evoked responses during the first 60 seconds after applying the current was not significantly influenced by the wetness of the birds. It was concluded that electrical stunning with low currents in wet birds leads to a lower prevalence of ventricular fibrillation at stunning and a shorter lasting stun in the non-fibrillated birds. This effect is possibly due to some of the current tracking over the bird's wet body rather than through the brain.     

Head-only electrical stunning of poultry using a waterbath: a feasibility study

1. The objective of this work was to investigate the feasibility of head only waterbath stunning as a means of generating immediate and long lasting unconsciousness while preventing wing flapping and avoiding carcass damage. 2. EEG measurements showed that immersion of the heads of the broilers for one second in a waterbath containing water of conductivity 2 x 5 mS/cm and a 50 Hz electric field of 10 V/cm resulted in immediate unconsciousness, and that increasing the electric field strength extended the duration of unconsciousness. 3. The passage of a 25-30 mA alternating current of frequency 2000 Hz through the broilers' bodies suppressed the wing flapping that followed a stun. 4. When the body current and electric field were applied simultaneously, wing flapping was prevented and EEG signals were suppressed for over 30 seconds indicating that the immediate unconsciousness lasted long enough to facilitate humane slaughter.     

Effect of depth of immersion in the waterbath on the effectiveness of electrical stunning in chickens.

Broiler chickens were electrically stunned either by immersing their heads, necks and upper breast in a waterbath stunner or by immersing their heads only. The time to recovery of muscular activity was assessed, and it was found that the deeper immersion was associated with a slightly (10 second) shorter time to resumption of head righting. When hens which had previously been implanted with electroencephalogram electrodes were electrically stunned it was found that the incidence of somatosensory evoked responses during the first 60 seconds after applying the current was not influenced by the depth of immersion. It was concluded that depth of immersion had little influence on the effectiveness of electrical stunning.     

Assessment of the effectiveness of head only and back-of-the-head electrical stunning of chickens

1. The study assesses the effectiveness of reversible head-only and back-of-the-head electrical stunning of chickens using 130–950 mA per bird at 50 Hz AC.

2. Three trials were conducted to compare both stunning systems: (a) behavioural assessment of return of consciousness, (b) insensibility to thermal pain, and (c) assessment of return of brain activity with visually evoked potentials (VEPs).

3. Assessment of behaviour suggested that the period of unconsciousness following head-only electrical stunning was shorter in hens compared to broilers.

4. Stunning across the back-of-the-head delayed the time to return of brainstem function compared to stunning with standard head-only electrodes. Additionally, back-of-the-head stunning produced a more prolonged period of electroanalgesia compared to head-only.

5. Based on examination of return of brain function with VEPs in hens, back-of-the-head stunning produced a shorter-lasting stun than standard head-only. However, even for standard head-only, the stun was notably shorter than previously reported. In some birds, brain function had returned within 9 s after the end of stunning.

6. The results suggest that some birds may recover consciousness prior to or during the neck cut. Based on these findings, back-of-the-head stunning and standard head-only stunning of hens should not be recommended without further development.

     

Observations during captive bolt stunning of rabbits]

78 rabbits of mixed breed and about 3 kg live weight were stunned before slaughter with a commercial spring operated captive bolt apparatus designed for rabbits and water fowl. The following reaction patterns were observed: 1.) Immediate onset of tonic spasm, followed by weak to heavy clonic spasms and/or subsequent relaxation; irreversible loss of corneal reflex and cessation of respiration: effective and irreversible stun tantamount to killing 2.) Same reaction as before except that respiration restarted after 1/2 to 2 min: effective but only temporary stun 3.) Similar reaction as before, but respiration maintained: insufficient stun 4.) Immediate onset of weak tonic spasm; respiration and corneal reflex maintained: insufficient stun. According to this classification 56 rabbits (72%) were killed outright and 18 (23%) temporarily stunned while in 4 (5%) the stun was ineffective. The captive bolt apparatus proved thus to be principally suited for the stunning resp. killing of slaughter rabbits. The best stunning results were obtained with shots into the parietal bone near the sagittal line but not hitting the bone sutures. To achieve this the apparatus has to be placed slightly paramedian on the front as close to the ears as possible. Insufficient stunning results could be blamed on deviating shooting positions. To avoid misses a good fixation of the animal including its head is necessary. Correct application provided the use of penetrating concussion stunners should be preferred to applying a blow to the neck for stunning rabbits.     

Effects of electrical water bath stunning current frequencies on the spontaneous electroencephalogram and somatosensory evoked potentials in hens

1. The effectiveness of water bath electrical stunning of chickens with a constant root mean square (rms) current of 100 mA per bird delivered for 3 s using 100, 200, 400, 800 and 1500 Hz sine wave alternating current (AC) was investigated in layer hens. The quantitative changes occurring in the electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) were used to determine the effectiveness of stunning. The changes occurring in the EEG were evaluated using Fast Fourier Transformations (FFT) and the SEPs were averaged to determine whether they were present or abolished. 2. The results of FFT indicated that stunning of chickens with a constant rms current of 100 mA per bird using 100 or 200 Hz induced epileptiform activity in all the hens, immediately followed by a reduction in the total (2 to 30 Hz) and relative (13 to 30 Hz) power contents in the EEG frequency bands indicative of unconsciousness and insensibility. The SEPs were abolished in the majority of hens stunned with 100 Hz and all the hens stunned with 200 Hz. 3. By contrast, stunning using 400, 800 or 1500 Hz failed to induce epileptiform activity in all the birds, the total and relative power contents in the EEG frequency bands showed a substantial increase, rather than reduction, and the SEPs were also retained in the majority of chickens. It is therefore suggested that stunning using these frequencies failed to stun them satisfactorily. In these birds, occurrence of a painful arousal, rather than unconsciousness, could not be ruled out. 4. It is therefore suggested that water bath electrical stunning of chickens with a minimum rms current of 100 mA per bird delivered using 100 or 200 Hz would be adequate to ensure bird welfare under commercial conditions, provided both the carotid arteries in the neck are severed at slaughter. On humanitarian and bird welfare grounds, a rms current of greater than 100 mA per bird should be applied whilst using frequencies of 400 Hz or more of sine wave AC for water bath electrical stunning of chickens.     

CO2-stunning of slaughter pigs: effects on EEG, catecholamines and clinical reflexes

Investigations were carried out on the response of slaughter pigs to CO2 stunning with two different gas concentrations (80 vol%, 90 vol%, 73 s) under practical conditions in a one gondola-dip-lift system. EEG measurements were performed and blood constituents such as catecholamines (adrenaline, nor-adrenaline) and lactate as well as clinical reactions (nasal septum and corneal reflex, heart beats) investigated. Special EEG-electrodes were adapted for the measurement on pigs and a mobile data logger was prepared for the use in the lairage of the slaughter house and in the stunning unit. The CO2 concentrations were measured continuously close to the head of the pigs when transported up and down in the stunning gondola. The results show that the technique is suited to monitor the effects of different CO2 gas concentrations on the EEG of the pigs under practical conditions. There is strong evidence that CO2 concentrations of 80 vol% applied over 70 s as required by law are not sufficient to stun pigs properly. A large part of the animals still showed typical reflexes when leaving the stunning pit. When an atmosphere of 90 vol% CO2 is applied, most animals are already dead before bleeding commences. This may create problems in respect to meat hygiene. The blood analysis revealed very high concentrations of catecholamines after stunning. The values for adrenaline and nor-adrenaline in the sticking blood rose by a factor of about 1000 as compared to the concentrations in blood samples taken in the lairage before stunning. It seems necessary to revise the current legislation on gas stunning and to look in greater detail in the effects of CO2 stunning on the welfare of slaughter pigs.     

Cortical function in cattle during slaughter: conventional captive bolt stunning followed by exsanguination compared with shechita slaughter

Brain function was examined in adult cattle after conventional captive bolt stunning or shechita slaughter, using eight animals in each treatment. The times to loss of evoked responses (visual and somatosensory) and spontaneous activity in the electro-corticogram were used to determine the onset of brain failure. Captive bolt stunning followed by sticking one minute later resulted in immediate and irreversible loss of evoked responses after the stun. Spontaneous cortical activity was lost before sticking in three animals, and in an average of 10 seconds after sticking in the remaining five animals. The duration of brain function after shechita was very variable, and particularly contrasted with captive bolt stunning with respect to the effects on evoked responses. These were lost between 20 and 126 seconds (means of 77 seconds for somatosensory and 55 seconds for visual evoked responses) and spontaneous activity was lost between 19 and 113 seconds (mean 75 seconds) after slaughter.     

Effect of the method of killing,interval between killing and neck cutting and blood vessels cut on blood loss in broilers

1. Broiler chickens were killed using 90% argon in air, or 30% carbon dioxide and 60% argon in air or 120 mA per bird in a waterbath with a 50 Hz alternating electric current. Ventral or unilateral neck cutting was performed at 1, 3 or 5 min after killing. In addition, a group of broilers was stunned with 120 mA per bird in a waterbath using 1500 Hz alternating current and were bled out with a ventral neck cut within 20 s from stunning.

2. Blood leaving the neck wound was collected in a bin placed on an electronic balance and a computer program calculated the cumulative blood loss up to 100 s after neck cutting.

3. Bleed‐out was significantly affected by killing method and time of neck cutting. Broilers killed with the carbon dioxide‐argon mixture bled‐out less than those killed with argon or 50 Hz electric current. When compared with the 1 min neck cutting interval, a delay of 3 or 5 min resulted in a lower bleed‐out. High frequency electrical stunning and ventral neck cutting within 20 s resulted in a slightly higher bleed‐out than those recorded for the killing methods. However, within argon killing, a delay of 3 or 5 min in ventral or unilateral neck cutting had no significant effect on the bleed‐out. In broilers killed with the carbon dioxide‐argon mixture a 3 min delay in ventral neck cutting or a 5 min delay in unilateral neck cutting resulted in lower bleed‐out.

4. Neck cutting of broilers within 5 min after argon killing or 3 min after killing with the carbon dioxide‐argon mixture would result in a satisfactory bleed‐out.     

Effect of a 350 Hz DC stunning current on evoked responses in the chicken's brain

Somatosensory evoked responses in the chicken's brain were examined before and after stunning with a 350 Hz pulsed DC. When the current was greater than 120 mA, 93 per cent of the birds lost their evoked responses for at least 60 seconds. On this basis 120 mA per bird is recommended as an acceptable current for commercial use.     

Electroencephalographic studies of calves associated with electrical stunning, throat cutting and carcass electro-immobilisation

Electroencephalographic (EEG) recordings were made on 34 calves (two days to six weeks old, 30-50 kg) during the slaughter process. The calves, supported in a V-shaped box or polypropylene net, were either head-only electrically stunned (50 Hz, 1.0 A) across the head and allowed to recover, head-only stunned followed by throat cutting or head-only stunned followed by throat cutting and electro-immobilisation. All time intervals were measured from the commencement of the stun. The electro-immobilisation (80 V peak, 14.3 Hz, 5 ms square wave) at 15-26 seconds post-stun was applied through electrodes attached to nose and anus, for periods ranging from 5-60 seconds. The head only stun produced an elevated EEG amplitude of the electroplectic fit which lasted approximately 34 seconds followed by a quiescent period before the EEG amplitude again became elevated above normal. A normal pre-stun pattern was not reached until many minutes had elapsed. Following the stun, the forelegs were usually flexed and then extended, gradually becoming part of the paddling movements commencing as early as eight seconds post-stun. Such movements were taking place while the animal was still stunned. With a head-only stun followed by throat cutting, the electroplectic fit was reduced to about 23 seconds and the amplitude of the EEG fell to about 10 microV after 50-73 seconds and breathing was inhibited for at least 20 seconds after stun commencement. If inadvertently only one carotid was severed, the EEG did not fall as rapidly as when both carotids were cut. The increase in amplitude of the EEG tracings was caused by stunning but the reduced duration of this increase in calves in which the throat was cut, suggests that there is an impairment of recovery of brain function from the moment of cutting and recovery of sensibility is unlikely. In reviewing the criteria of sensibility, we believe that insensibility can be presumed to continue from stun initiation, through the throat cut until the EEG falls below 10/microV provided that there is no resurgence of activity and the EEG amplitude continually falls rapidly enough. By this criteria, calves which are electrically stunned and rapidly exsanguinated remain permanently and irreversibly insensible. The addition of at least 15 seconds electro-immobilisation causes an even more rapid fall in the amplitude of the EEG (<10 microV at 50 seconds) making insensibility more certain as well as abolishing animal movement.     

Commercial slaughter methods used on Atlantic salmon: determination of the onset of brain failure by electroencephalography

This study investigated the effect of exsanguination without prior stunning, or carbon dioxide narcosis followed by exsanguination, or percussive stunning or spiking the brain, on the time taken to abolish the visual evoked responses (VERS) of farmed Atlantic salmon. Only percussive stunning and spiking killed the fish immediately and the other two methods resulted in aversive reactions by the fish. The VERS were lost between 148 and 440 seconds after exsanguination without stunning, and between 300 and 554 seconds after carbon dioxide narcosis followed by exsanguination. During both these procedures the fish showed strong aversive behaviour. In contrast, percussive stunning and spiking the brain could result in the immediate loss of VERS and no aversive reactions from the fish if the stun was applied correctly.     

Reflexes and loss of sensibility following head-to-back electrical stunning in sheep

The effects of head-to-back electrical stunning on the incidence of post-stunning reflex activity and cortical evoked responses were investigated in sheep. The stuns were effective in terms of inducing epileptiform activity and they resulted in cardiac fibrillation which ensured that there was no recovery of consciousness. Even though the corneal reflex and respiratory gasps were present, in 10 out of 12 sheep there were no concomitant visual and somatosensory evoked responses following a stun. In the remaining two, the responses were rudimentary and it would be unwise to conclude that the animals were conscious. It is suggested that brain stem reflexes following this stunning method should not be relied on as indices of recovery. The results support the view that an electrical stunning method which induces cardiac fibrillation results in improved animal welfare.     

Effect of slaughter on the spontaneous and evoked activity of the brain

The principal blood vessels in the neck which are severed at slaughter in commercial poultry processing plants are described. Mechanical slaughtering methods often severed the spinal cord without cutting the carotid arteries. The manual method of slaughter cut one carotid artery plus one jugular vein. The effects of 9 different slaughtering methods on spontaneous and evoked electrical activity in the brain were examined in anaesthetised chickens and ducks. Severing the spinal cord without cutting the carotid arteries was found to result in death from asphyxia, and cutting one carotid artery plus one jugular vein was one of the slowest methods of killing the birds. Inducing a cardiac arrest at electrical stunning was the quickest method of inducing death. Spontaneous activity in the brain was lost before visual evoked activity. The times before loss of spontaneous activity varied between 23 and 233 s according to the method of slaughter and loss of evoked activity ranged between 90 and 349 s after slaughter.