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.     

Broiler carcass quality using head-only electrical stunning in a waterbath

1. The objective was to assess carcass quality of broilers when they were stunned by immersing their heads in a waterbath with an electric current flowing from one side of it to the other, while a second small current passed through the body to the waterbath to prevent involuntary wing flapping. 2. The prevalence of wing, shoulder and breast fillet haemorrhages and of broken bones in the pectoral region was not greater than that resulting from the normal stunning practice in that plant (63 mA, 610 Hz pDC). 3. These results imply that carcass damage using this technique will be significantly lower than that which will result from the application of higher stunning currents required by the new EU slaughter poultry slaughter regulations.     

Comparison of the histological and histochemical properties of skeletal muscles between carbon dioxide and electrically stunned chickens

1. Histological and histochemical profiles of Musculus pectoralis (PT, type IIB fibres), M. iliotibialis lateralis (ITL, types IIA + IIB fibres) and M. puboischiofemoralis pars medialis (PIF, type I fibres) were compared in carbon dioxide (37%, 70 s) and electrically (14 V, 5 s) stunned male chickens. 2. Muscle materials were taken at 0, 4 and 24 h from carcases dressed and cooled with ice-water mixture for 30 min. Glycogen and fat contents, and adenosine triphosphatase and reduced nicotinamide adenine dinucleotide dehydrogenase activities of fibres were measured. 3. In PT muscle at 0 h, gas stunned chickens showed many fibres with high glycogen content but those electrically stunned contained few such fibres. Fibres from gas stunned birds had lost almost all their glycogen after 24 h of cold storage. 4. In the ITL muscle of gas stunned chickens at 0 h residual glycogen was observed in type IIB fibres. In contrast, in the electrically stunned birds it was in type IIA, showing the different effects of the stunning methods. During cold storage, glycogen disappeared earlier in type IIB than IIA fibres. 5. In PIF muscle with fibres of low glycogen content, the gas stunned chickens maintained a good fibre structure for 4 h or more, but the electrically stunned had already lost intact fibre structure at 4 h. 6. These results indicated that the carbon dioxide stunning was a better method for chicken welfare and meat quality than electrical stunning.     

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.     

Inhalation of water during electrical stunning in chickens

Twenty live hens were subjected to electrical stunning using a waterbath containing a solution of technetium99 (99Tc), and 12 hen carcases were injected intratracheally with different doses of the same solution. The respiratory tract was dissected from the carcases and samples were assessed for the presence of radioactivity. Thirty-five per cent of the electrically stunned birds had 99Tc in their tracheas and 15 per cent had 99Tc in the lungs. From the dose response study it was estimated that the birds with radioactivity in their lungs had inhaled between 0.5 and 1 ml of water. In commercial slaughterlines this may be a hazard to meat hygiene.     

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.     

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 very low pulsed direct currents at high frequency on the return of neck tension in broilers

Broiler chickens were stunned electrically for one second or 10 seconds with a unipolar pulsed direct current (DC) at 550 Hz. The effectiveness of the stun was assessed from the birds' behaviour. All the birds were stunned effectively when more than 15 mA true root mean square DC was applied for either period. An increase in the duration of the applied current resulted in an increased duration of unconsciousness. However, the unipolar pulsed DC at 550 Hz did not induce cardiac arrest, and it must therefore be accompanied by a prompt and effective neck cut, severing both carotid arteries.     

Jugular venous emboli of brain tissue induced in sheep by the use of captive bolt guns

Emboli of central nervous tissue were detected in the jugular venous blood of two of 15 sheep stunned with a conventional cartridge-operated captive bolt gun and in two of 15 sheep stunned with a pneumatically activated gun. No emboli were detected in arterial blood from these sheep or in venous blood from sheep stunned electrically. Emboli from an animal with BSE could transmit the disease to people.     

The effect of different slaughter methods on the post mortem glycolysis of muscle in lambs

Differences in muscular activity and rates of decline in the pH of the M. longissimus dorsi of lambs subjected to different methods of stunning and slaughter were observed. Lambs electrically stunned by a head-to-leg method had significantly lower initial pH values as compared to animals stunned by an electrical head-only method, or by captive bolt, or without any form of stunning prior to slaughter. When electrical stunning by a head-to-leg method was combined with low voltage (24 V) electrical stimulation during slaughter and bleeding, mean pH values declined at the highest rate and fell to approximately 6.0 within two hours of slaughter. This last procedure, therefore, has the potential to greatly reduce times between slaughter and freezing without increasing the risk of cold shortening and the associated toughness of meat.     

Sensory evaluation of breast fillets from argon‐stunned and electrically‐stimulated broiler carcases processed under commercial conditions

1. A comparison of eating quality of breast meat (pectoralis major) filleted at 2 h post‐mortem was made between broilers stunned with argon‐induced anoxia (less than 2% residual oxygen) and broilers which were electrically‐stunned and their carcases electrically‐stimulated under commercial conditions.

2. Fifty breast muscles were filleted from the carcases of argon stunned broilers at 2 h post‐mortem. Fifty breast muscles were also removed at the same time from the carcases of broilers which were electrically‐stunned and electrically‐stimulated. A ‘control’ group of broilers which were electrically‐stunned and electrically‐stimulated and processed under as similar conditions as possible were also filleted after overnight ageing in the air chiller.

3. Sensory analysis was performed using 10 trained panelists, who were asked to rate the fillets on a 1 to 8 hedonic scale for taste, texture, juiciness and overall liking.

4. The mean ranks for texture and overall liking differed between the groups. The mean ranks based on texture were the highest for control, intermediate for argon stunning and the lowest for electrical stimulation treatment group. The mean ranks based on overall liking were similar for the control and argon stunning groups, and their ranks were higher than that of electrical stimulation treatment group. The mean ranks for taste and juiciness did not differ significantly between the groups.

5. It is concluded that, in comparison with electrical stimulation of broiler carcases soon after plucking, stunning broilers with argon‐induced anoxia produced tender breast meat when filleted at 2 h postmortem.     

Sheep slaughtering procedures. I. Survey of abattoir practice

The stunning-to-sticking interval (taken as the time between the start of stunning and the first appearance of blood from the sticking wound) was measured in over 10000 sheep at 40 abattoirs in Great Britain, and the stunning duration was determined for those sheep which were electrically stunned. Stunning duration lasted, on average, for 4 sec where low voltage (94 V) low frequency (50 Hz) stunning was used, and for 3 sec with low voltage (133 V) high frequency (1542 Hz) stunning. The average stunning-to-sticking interval was 40 sec in sheep stunned by captive bolt, and 21 sec for those receiving electrical stunning. Ninety-nine % of the sheep in the survey were stuck within 82 sec of stunning.It is concluded that stunning should induce an anaesthesia which lasts for 82 sec plus the time necessary for sticking to result in brain death if it is to be effective from a humanitarian standpoint for the majority of the sheep population in Great Britain.     

The effect of different slaughter methods on the post mortem glycolysis of muscle in lambs

Differences in muscular activity and rates of decline in the pH of the M. longissimus dorsi of lambs subjected to different methods of stunning and slaughter were observed. Lambs electrically stunned by a “head-to-leg” method had significantly lower initial pH values as compared to animals stunned by an electrical “head-only” method, or by captive bolt, or without any form of stunning prior to slaughter. When electrical stunning by a “head-to-leg” method was combined with low voltage (24V) electrical stimulation during slaughter and bleeding, mean pH values declined at the highest rate and fell to approximately 6.0 within two hours of slaughter. This last procedure, therefore, has the potential to greatly reduce times between slaughter and freezing without increasing the risk of cold shortening and the associated toughness of meat.     

Effect of stunning current on downgrading in turkeys

1. Turkeys were electrically stunned with 75, 150 or 250 mA per bird to examine the effect of current on carcase quality defects. The defects that were examined included skin and muscle haemorrhaging, broken bones and engorgement of veins with blood. 2. The incidence of ventricular fibrillation at these currents was 26, 97 and 100%, respectively. Haemorrhaging in the breast muscle was the only variable affected by stunning current and was greatest when 250 mA was used. 3. It is recommended that turkeys should be stunned with 150 mA per bird.     

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.     

Prevalence and duration of insensibility following electrical stunning in calves

Sixty-one calves were electrically stunned with 100-250 V currents (103-1806 mA) and the prevalence and duration of insensibility was assessed from their physical behaviour, the presence of epileptiform activity in their electrocorticograms, and the absence of visual evoked responses in their electrocorticograms. A current applied at 100 V across the head for 3 s failed to induce insensibility in all cases. Currents at 150-250 V induced insensibility in all calves and the shortest duration of insensibility was 44 s. It is recommended that a 150-200 V current would be appropriate for commercial use.     

Effect of stunning method and filleting time on sensory profile of turkey breast meat

1. Twenty four 22 week‐old large stags were stunned using one of two methods, argon‐induced anoxia (2% residual oxygen) or an electric current (150 mA per bird, 50 Hz). The birds were processed under commercial conditions and carcasses held at 3°C until the breast muscles were filleted at either 3 h after killing or after overnight maturation.

2. The meat samples were frozen at — 40° C and stored at — 20°C until they were thawed at 1°C and cooked at 85°C. They were subjected to sensory evaluation by 10 experienced assessors and instrumental texture measurements were made.

3. Only stunning method had significant effects on the sensory profile and instrumental texture. Breast meat from anoxia‐stunned turkeys was less firm on cutting, more tender and had a more powdery residue on eating than that from electrically‐stunned turkeys. The instrumental texture values confirmed that breast meat from anoxia‐stunned turkeys was more tender than that from the electrically‐stunned turkeys.

4. There was no significant correlation between the subjective tenderness rating and the instrumental texture value.

5. Principal components analysis showed that 59% of total variation was explained by the first two dimensions, the first being a contrast between turkeys that were tender and powdery and those that were firmer and fibrous. When values from individuals were plotted, this dimension was related to the differences between anoxia and electrical stunning, with anoxia‐stunned turkeys at the tender end of the first dimension.     

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.     

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.     

Percussion stunning of sheep

Extract

Sir, — As from October 1976, all sheep in this country will have to be stunned prior to slaughter. Until recently it had been widely assumed that some form of electrical stunning would be the only practical method for use in New Zealand freezing works. Although for several years electrical stunning has been used for pigs in this country and other classes of stock overseas, only one meat export works in New Zealand has been stunning sheep electrically as a routine procedure for a complete season.