An assessment of carbon dioxide stunning in pigs

The vocalisation patterns of pigs subjected to stunning in 86 per cent carbon dioxide in a commercial abattoir suggested that narcosis began 30 to 39 seconds after the start of the immersion procedure. The spontaneous and reflex physical behaviour of the pigs after immersion indicated that they were effectively stunned, but the majority of the animals were not considered to be brain-stem dead. None of the carcases showed pale soft exudative meat.     

Changes in the spontaneous and evoked electrical activity in the brain of hens during stunning with 30 per cent carbon dioxide in argon with 5 per cent residual oxygen.

Changes in the somatosensory evoked potentials (SEPs) and spontaneous electroencephalogram (EEG) in hens were investigated during stunning with a mixture of 30 per cent carbon dioxide in argon with 5 per cent residual oxygen. The results showed that the SEPs were lost on average in 17 seconds (maximum 28 seconds), which is similar to the 19 seconds (maximum 32 seconds) reported while stunning hens with a mixture of 30 per cent carbon dioxide in argon with 2 per cent residual oxygen. The spontaneous EEG showed suppression and a quiescent phase at 14 and 58 seconds, respectively. It is concluded that a mixture of 30 per cent carbon dioxide in argon with 2 per cent residual oxygen would be ideally suited for batch stunning chickens and any inadvertent increase in the residual oxygen level up to 5 per cent in the stunning atmosphere would not lead to inadequate stunning or recovery of consciousness before neck cutting.     

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 carbon dioxide stunning on somatosensory evoked potentials in hens

The spontaneous electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) were examined in 17 hens before and during stunning in 45 per cent carbon dioxide. The results indicated that EEG suppression and loss of SEPs occurred in 21 +/- 4 s and 30 +/- 2 s, respectively, after exposure to carbon dioxide, eventually leading to EEG silence in 101 +/- 18 s. Convulsions occurred 15 seconds after the loss of SEPs, suggesting that the hens convulsed while they were unconscious. It is concluded that the induction of anaesthesia can be rapid in carbon dioxide stunning and in this respect carbon dioxide is potentially suitable for stunning poultry under commercial conditions.     

Efficiency of bleeding of broilers after gaseous or electrical stunning

The efficiency of bleeding of broilers (g blood/kg liveweight) was measured after stunning them with either 45 per cent carbon dioxide in air for two minutes or with 2 per cent oxygen (achieved by displacing air with argon) for two minutes or with an electric current (77 or 104 mA at 50 Hz for four seconds). The results indicated that the initial rate of bleeding was higher in the electrically stunned broilers with non-fibrillated hearts than in the gas stunned broilers and electrically stunned broilers with fibrillated hearts. This difference was significant up to 60 seconds after neck cutting (P less than 0.05) but after 140 seconds all the broilers had bled out to a similar extent (30 to 33 g/kg liveweight). It is concluded that after gas stunning the time interval between neck cutting and scalding should be 60 to 140 seconds.     

Survival rate and carcase downgrading after the stunning of broilers with carbon dioxide-argon mixtures.

As chickens may rapidly regain consciousness after gas stunning, the effects of a two minute exposure to a carbon dioxide-argon mixture on survival rate were investigated. Broilers were stunned in batches of 10 per transport crate with a mixture of 10, 20 or 30 per cent carbon dioxide in argon with 5 per cent residual oxygen. The birds were exposed to the gaseous atmosphere for two minutes. A control group of birds was electrically stunned (120 mA for four seconds; 50Hz sinusoidal waveform). In addition, the incidence of carcase downgrading conditions after stunning with 20 per cent or 30 per cent carbon dioxide in argon with 5 per cent residual oxygen was compared with the incidence after electrical stunning. The results showed that stunning with 10 and 20 per cent carbon dioxide in argon with 5 per cent residual oxygen resulted in survival rates of 24 and 1 per cent, respectively. Stunning with 30 per cent carbon dioxide in argon with 5 per cent residual oxygen resulted in the death of all the broilers. Electrical stunning resulted in a significantly (P less than 0.001) larger number of broilers with breast muscle haemorrhaging and broken furculum and coracoid bones, whereas stunning with gas mixtures resulted in a significantly (P less than 0.001) higher incidence of broilers with damaged wing bones. Electrical stunning of broilers resulted in a significantly higher pH in the breast muscles 20 minutes post mortem than stunning with carbon dioxide-argon mixtures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of slaughter by removal from water on visual evoked activity in the brain and reflex movement of rainbow trout (Oncorhynchus mykiss)

The effects of removal from water and death by anoxia on brain function and reflex movement were examined in conscious trout. Visual evoked responses (VERS) were measured in fish with a body temperature of 20 degrees C, 14 degrees C and 2 degrees C. On average the fish took 2.6 minutes at 20 degrees C, 3.0 minutes at 14 degrees C and 9.6 minutes at 2 degrees C to lose VERS, and 11.5, 27.7 and 197.6 minutes, respectively, to lose all movement. VERS were absent from fish anaesthetised with MS222. From a humanitarian standpoint these results indicate that fish killed by anoxia could be exposed to periods of distress or suffering, and that cooling them in ice prolongs this period.     

Onset of insensibility at slaughter in calves: effects of electroplectic seizure and exsanguination on spontaneous electrocortical activity and indices of cerebral metabolism.

Cerebral venous and femoral arterial blood samples were collected from 21 young calves either during electrical stunning and recovery or electrical stunning and slaughter by carotid severance or slaughter without stunning. The blood samples were analysed for PO2, PCO2, pH, glucose and lactate. The results were compared with simultaneous recordings of spontaneous electrocortical (ECOG) activity. Calves subjected to head-only electrical stunning and slaughter became permanently insensible at the time of the stun. The six calves slaughtered without stunning lost sensibility within 10 seconds. One calf, in which a clot formed in the carotid arteries inhibiting bleeding, maintained some evidence of cortical activity beyond 52 seconds; this was high amplitude low frequency activity and analysis by Fast Fourier Transform showed sensibility was not regained. In the remaining calves the ECOG activity was lost on average within 49 +/- 3.5 (SEM) seconds after slaughter. The cerebral extraction of metabolites increased after carotid severance, indicating inadequacy of cerebral bloodflow after slaughter. No correlations were found between indices of cerebral metabolism and the time of loss of cortical function.     

A survey of slaughter procedures used in chicken processing plants

Information was collected on the slaughter procedures used in 12 processing plants in Australia. The processing line speed varied from 25 to 125 birds/minute; the voltage in the electrified waterbath varied from 55 to 165 V; the duration of stunning was 2.0 to 7.5 seconds and the time allowed for exsanguination was 45 to 180 seconds. As a result of the variables, some birds were dead on leaving the stunner and prior to exsanguination, while it was probable that others were not dead before entering the scald tank.     

Changes in the somatosensory evoked potentials and spontaneous electroencephalogram of hens during stunning with a carbon dioxide and argon mixture.

A previous investigation indicated that when hens were exposed to 2% oxygen in argon (anoxia) EEG suppression and loss of SEPs occurred at 17 and 29 s after exposure. In this study, hens were exposed to 49% carbon dioxide in air (hypercapnic hypoxia) or 31% carbon dioxide with 2% oxygen in argon (hypercapnic anoxia) and their spontaneous electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) were investigated. The results indicated that EEG suppression and loss of SEPs occurred in 11 and 26 s, respectively, in hypercapnic hypoxia. These events occurred at 11 and 19 s, respectively, after exposure to hypercapnic anoxia. These results indicated that, with regard to preslaughter stunning/killing of chickens, a mixture of 31% carbon dioxide with 2% oxygen in argon resulted in a more rapid loss of evoked responses in the brain when compared with 49% carbon dioxide in air or with 2% oxygen in argon. It is concluded that stunning chickens with low concentrations of carbon dioxide in argon would result in a more rapid loss of consciousness.     

Effects of transport, lairage and stunning on the concentrations of some blood constituents in horses destined for slaughter

The aim of the present study was to determine, in horses destined to slaughter, the effects of transport, lairage and stunning on some blood constituents related to stress. Twenty one horses culled from a race track due to poor athletic performance, transported weekly to a nearby slaughterhouse were used. Each horse was canulated through venipuncture of the right jugular vein with a central venous catheter which remained permanently until after the exsanguination. Through the catheter, blood samples were taken at 6 sampling times: one hour before loading of the horses, immediately after loading, at the end of the journey, immediately after unloading, after lairage, in the stunning box before stunning and during exsanguination. Blood samples were analyzed for the following variables: plasma lactate concentration, plasma creatine phosphokinase activity (CK), plasma glucose concentration, plasma cortisol concentration and packed cell volume (PCV). Time in the stunning box, number of stunning attempts, presence of return to consciousness signs and time between stunning and sticking were also recorded. The results for pre-mortem variables were: mean time in the stunning box 9 min 48 sec, 85.7% of the horses fell at the first stunning attempt, 57.2% of the horses showed signs of returning to consciousness after stunning and the most frequent interval between stunning and sticking was 1.01 to 2 min. Mean values for the blood variables showed a significant rise (P < 0.05) in the concentrations of lactate, glucose and cortisol, as well as CK activity and PCV during transport. The highest values for these blood constituents were seen before stunning and during exsanguination, except for cortisol concentration, which showed the highest values during the transport process.     

Survey of the effectiveness of stunning procedures used in Spanish pig abattoirs

Two pig abattoirs (A and B) equipped with an automated head-only and head-to-chest electrical stunning system, and two (C and D) equipped with a manual carbon dioxide stunning system, were evaluated to compare the effectiveness of stunning in a total of 10,454 pigs slaughtered under commercial conditions. In the abattoirs with the electrical stunning system, the percentage of animals that responded to a nose prick was significantly lower (P<0.05) in abattoir B, where a higher current intensity was used (P<0.05), than in abattoir A. No righting reflex was observed in the electrically stunned pigs. In the abattoirs with the carbon dioxide stunning system, the percentage of animals that responded to a nose prick and showed a righting reflex was significantly lower (P<0.05) in abattoir C, where the duration of the carbon dioxide cycle was longer and the interval between discharge from the system to sticking was shorter (P<0.05), than in D. Comparing the electrical and carbon dioxide stunning systems, the pigs stunned with carbon dioxide were significantly more responsive to a nose prick (P<0.05) and 25 per cent of them showed a righting reflex. Under the conditions of the study the fully automated head-only stunning with additional chest electrodes appeared to be more effective and less susceptible to incorrect handling than the manual carbon dioxide stunning system.     

Investigation into the batch stunning/killing of chickens using carbon dioxide or argon-induced hypoxia

Three hundred and twenty broilers were stunned for 2 minutes in batches of 10 per crate in four treatments: 45 per cent carbon dioxide; 55 per cent carbon dioxide; 2 per cent oxygen, or 5 per cent oxygen presented as air diluted by argon. The number of survivors and the time to resumption of consciousness were recorded using the time to eye opening and response to comb pinching as indicators of consciousness. In 45 per cent and 55 per cent carbon dioxide and 2 per cent oxygen, 28, none and eight birds, respectively, survived out of 100 in each group. In 5 per cent oxygen the birds were still fully conscious after a 2 minute exposure period, and the test was discontinued. The time to recovery could be rapid after stunning in both the gases. It is suggested that a concentration of 55 per cent carbon dioxide or less than 1 per cent oxygen are required to kill broilers within a 2 minute exposure period, and that care should be taken to ensure that there is sufficient turbulence within the stunning chamber to avoid air pockets being trapped between the birds.     

Neuropathological changes produced by non-penetrating percussive captive bolt stunning of cattle

A blunt, non-missile head injury inflicted by a non-penetrating captive bolt pistol in cattle at slaughter resulted in immediate loss of consciousness, a depressed fracture of the frontal bone and widespread subarachnoid haemorrhage, particularly beneath the impact site, in the temporal and frontal lobes, and around the brainstem. There was also invariably petechial haemorrhage in the basal ganglia and thalamus. The large concussive force applied to the cranium by the stunner was probably responsible for rendering the animal insensible and the vascular damage produced by this force and the sudden ventrocaudal acceleration of the brain after impact. These findings supported the use of this mode of stunning, followed by exsanguination, as an acceptable form of slaughter of cattle in abattoirs.     

Neuropathological changes produced by non-penetrating percussive captive bolt stunning of cattle

A blunt, non-missile head injury inflicted by a non-penetrating captive bolt pistol in cattle at slaughter resulted in immediate loss of consciousness, a depressed fracture of the frontal bone and widespread subarachnoid haemorrhage, particularly beneath the impact site, in the temporal and frontal lobes, and around the brainstem. There was also invariably petechial haemorrhage in the basal ganglia and thalamus. The large concussive force applied to the cranium by the stunner was probably responsible for rendering the animal insensible and the vascular damage produced by this force and the sudden ventrocaudal acceleration of the brain after impact. These findings supported the use of this mode of stunning, followed by exsanguination, as an acceptable form of slaughter of cattle in abattoirs.     

Head-only followed by cardiac arrest electrical stunning is an effective alternative to head-only electrical stunning in pigs

Many small slaughter facilities use head-only electrical stunning to render swine unconscious and insensible to pain before slaughter. Head-only electrical stunning is a reversible procedure that is optimally effective for approximately 15 s after stun completion. In many small North American slaughter plants, the authors have observed hoist speeds that are too slow to achieve a short enough stun-to-bleed interval to maintain insensibility through exsanguination. Unlike many European plants, there is no separate high-speed hoist for pigs and exsanguination on the floor is not condoned. As a result, a 2-stage stunning method was proposed where head-only stunning for 3 s was immediately followed by application of the same stunning wand to the cardiac region of the animal for 3 s while lying in lateral recumbancy. A paired-comparison study was conducted on 89 pigs in a small slaughter facility to compare the head-only method applied for 6 s with the head/heart method. The objective was to evaluate signs of return to sensibility, stun-to-bleed time, blood lactate concentration, muscle pH, drip loss, and fresh meat color to validate the head/heart electrical stunning method for small slaughter plants. Incidence of corneal reflex was not different (P > 0.05) between head/heart (93.8%) and head only (85%) stunning. Nose twitching was more common (P < 0.05) in head only (26.5%) than head/heart (5%) stunning. Head/heart stunning eliminated rhythmic breathing, natural blinking, eye tracking to moving objects, and righting reflex, which were all observed in head-only stunned pigs. Eye tracking to moving objects was observed in 40.8% of head-only stunned pigs. Blood lactate was not different (P > 0.05) between stunning methods (head only: 8.8 ± 0.7 mmol/L, head/heart: 7.8 ± 0.7 mmol/L). Stun-to-bleed time did not differ (P > 0.05; head only: 32 ± 1 s, head/heart: 33 ± 1 s). Mean time to loss of heartbeat with the head-only method was 121 ± 5 s. No heartbeat was observed with the head/heart method. Longissimus thoracis pH, color, and drip loss were not different (P > 0.05) between stunning methods. This study determined that the head/heart electrical stunning method reduces the incidence of signs of return to sensibility without significant effects on meat quality, plant operation speed, or blood lactate concentration. In addition, the head/heart method requires no capital investment for plants that are currently using the head-only method.     

Evaluation of stunning/killing methods for quail (Coturnix japonica): bird welfare and carcase quality.

1. The welfare and carcase quality implications of stunning/killing 7-week-old Japanese quail with either an electric current, 90% argon in air or a mixture of 30% carbon dioxide and 60% argon in air were investigated in 3 separate experiments. 2. The results showed that exposure of quail to either argon or the carbon dioxide-argon mixture resulted in loss of posture on average at 9 and 8 s respectively. In both gas mixtures, convulsions started 6 s after the loss of posture and the duration of clonic phase (wing flapping) did not differ significantly between the 2 gas mixtures. However, the duration of the tonic phase was found to be slightly longer with the carbon dioxide argon mixture than with argon alone (P<0.05). 3. The absence of a positive response to toe pinching performed soon after the loss of posture indicated that the birds became unconscious and insensible to pain before the onset of convulsions. 4. Carcase dissection showed that, in comparison with the electrical stunning, gas stunning/killing of quail in transport containers eliminated the problem of broken bones and significantly reduced haemorrhaging in breast and leg muscles.     

Plasma beta-endorphin increase following electrical stunning in sheep

Plasma concentrations of beta-endorphin were assayed in 10 sheep during the conscious state and in relation to electrical stunning. There was a 2 fold increase after stunning, and a further elevation following recovery. On this basis it is possible that recovery from electrical stunning at slaughter may cause undue distress, and it is suggested that exsanguination must be carried out promptly.     

Electrical stunning of red deer (Cervus elaphus)

Eighteen of 23 red deer (Cervus elaphus) at a deer slaughtering premises were successfully stunned with an apparatus modified from that normally used to stun sheep. The five unsuccessful electrical stuns were associated with poor head restraint and poor head contact by the electrodes. The median stunning current was 0.9 A, and in the majority of cases the duration of stunning was less than 1 second. The signs of the electrically induced epileptiform seizures in the deer were dissimilar to those seen in sheep, cattle and pigs, in that the initial tonic phase was less marked, and of shorter duration. A similar shorter and less obvious tonic phase was noted in four deer shot with a captive bolt pistol. Two animals which were electrically stunned, and bled within 10 seconds, showed no signs of recovery while bleeding. The electroencephalograms of four deer stunned with currents of 1.3 A for a duration of either 0.5 or 1.0 seconds were recorded under more controlled conditions. All four animals developed electroencephalograms typical of an epileptiform seizure. The animals exhibited behavioural reactions similar to the other 18 animals in the trial at the deer slaughtering premises and were rendered unconscious for between 54 and 122 seconds. The electroencephalogram activity amplitude was greater than that recorded immediately before stunning and took between 6 and 9 seconds to build up to maximum value. It is concluded that, providing the heads of deer are adequately restrained, head-only electrical stunning can be incorporated into a humane method of slaughter for deer.     

Electrocardiograms as an aid in assessing the stunning of cattle and pigs

Electrocardiograms (ECG's) were made from cattle and pigs after slaughter using only the left arm and right arm recording electrodes of a portable electrocardiogram with 12 recording electrodes. Functional heart activity was demonstrated in cattle after stunning with a captive bolt, nonpenetrative percussive methods and a head-only electrical technique. Recordings compatible with ventricular fibrillation were made in the majority of cattle and pigs subjected to a head-to-chest form of electrical stunning. In cases where the placement of stunning electrodes was defective, functional cardiac activity could be detected. Movement artefact on the ECG trace associated with epileptiform seizures following head-only electrical stunning was a technical problem. This was reduced by restunning the animal with a captive bolt before taking an ECG. The examination of ECG's made subsequent to slaughter could form an important component of the quality control of Halal slaughter or a slaughter process using the head-to-body electrical stunning techniques. Adoption of this would be facilitated by the development of a more simple and less sensitive electrocardiograph than that used in the present investigation.