Effectiveness of different electrical stunning regimens for turkeys and consequences for carcase quality

This study examined the effectiveness of electrical stunning of turkeys applied at 150 mA per bird utilising a range of waveform-frequency combinations. In addition, the effect of stunning treatment on subsequent carcase quality was examined. The effectiveness of stunning, as judged by time to recovery, was similar regardless of bird weight or applied stunning treatment. Increasing waveform frequency was associated with a decrease in the prevalence of ventricular fibrillation, although turkeys appeared more susceptible than broilers. Use of the higher frequency waveforms (500 and 1500 Hz) was associated with a marked improvement in carcase quality, particularly with regard to breast muscle haemorrhaging and their use may result in considerable commercial advantage.     

Effect of frequency of the stunning current waveform on carcase and meat quality of turkeys processed in a commercial plant in the UK

1. This study compared the effects of electrical stunning delivered using high and low frequency waveforms on carcase and meat quality of turkeys processed under commercial conditions. 2. The use of a high frequency waveform (1400 Hz) resulted in a faster bleedout and an improvement in carcase quality associated with a substantial reduction in haemorrhagic downgrading conditions. 3. Frequency of the applied waveform influenced breast muscle pH and colour although the magnitude of the differences was considered to be of minimal significance in influencing consumer perception.     

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 stunning current on carcase quality in chickens

The effect of the stunning current at slaughter on carcase quality was examined in 1845 broiler chickens. As the current was increased there was an increase and then a decrease in the incidence of red wingtips and in haemorrhages of the wing veins and the shoulder joint. The incidence of deep breast muscle haemorrhages increased above about 130 mA, and the incidence of broken bones increased between 75 and 170 mA. The incidence of carcase defects was lowest when either less than 130 or greater than 190 mA was used to stun the birds.     

Carcase and meat quality in ducks killed with either gas mixtures or an electric current under commercial processing conditions

1. The feasibility of killing 7-week old Peking ducks with gas mixtures and their effects on carcase and meat quality were evaluated and compared with killing in electrical waterbath under commercial conditions. 2. The prevalence of carcase appearance defects and broken bones in the carcases and haemorrhaging, pH, colour, cooking loss and texture of breast muscles were determined. 3. Ducks can be killed within 3 min by exposure to either 90% argon in air or a mixture of 30% carbon dioxide and 60% argon in air. 4. Gas or controlled-atmosphere killing of ducks, whilst they are still in their transport containers, would eliminate some of the welfare concerns associated with the conventional electrical waterbath stunning systems, without adversely affecting carcase and meat quality.     

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.     

Controlled atmosphere stunning of broiler chickens. II. Effects on behaviour, physiology and meat quality in a commercial processing plant

1. The effects of controlled atmosphere stunning on behavioural and physiological responses, and carcase and meat quality of broiler chickens were studied experimentally in a full scale processing plant. 2. The gas mixtures tested were a single phase hypercapnic anoxic mixture of 60% Ar and 30% CO(2) in air with <2% O(2), and a biphasic hypercapnic hyperoxygenation mixture, comprising an anaesthetic phase, 40% CO(2), 30% O(2), 30% N(2), followed by an euthanasia phase, 80% CO(2), 5% O(2), 15% N(2). 3. Birds stunned with Ar + CO(2) were more often observed to flap their wings earlier, jump, paddle their legs, twitch and lie dorsally (rather than ventrally) than those stunned with CO(2) + O(2). These behaviours indicate a more agitated response with more severe convulsions during hypercapnic anoxia, thereby introducing greater potential for injury. 4. Heart rate during the first 100 s of gas stunning was similar for both gases, after which it remained constant at approximately 230 beats/min for CO(2) + O(2) birds whereas it declined gently for Ar + CO(2) birds. 5. In terms of carcase and meat quality, there appeared to be clear advantages to the processor in using CO(2) + O(2) rather than Ar + CO(2) to stun broiler chickens, for example, a much smaller number of fractured wings (1.6 vs. 6.8%) with fewer haemorrhages of the fillet. 6. This study supports the conclusions of both laboratory and pilot scale experiments that controlled atmosphere stunning of broiler chickens based upon a biphasic hypercapnic hyperoxygenation approach has advantages, in terms of welfare and carcase and meat quality, over a single phase hypercapnic anoxic approach employing 60% Ar and 30% CO(2) in air with <2% O(2).     

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.     

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.     

An investigation into the batch killing of turkeys in their transport containers using mixtures of gases

This study was carried out under commercial conditions to investigate the feasibility of killing turkeys while they were still in their transport containers, with a mixture of gases, and to compare the effects of this method and electrical stunning on the prevalence of carcase downgrading conditions and haemorrhages in the breast muscles. The results showed that turkeys could be readily killed while still in their transport containers by using either anoxia induced with 90 per cent argon in air or hypercapnic anoxia induced with a mixture of 30 per cent carbon dioxide and 60 per cent argon in air, and that the prevalence of carcase-downgrading conditions and haemorrhages in the breast muscles was lower after killing the turkeys with the gases.     

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.     

Controlled atmosphere stunning of broiler chickens. I. Effects on behaviour, physiology and meat quality in a pilot scale system at a processing plant

1. The effects of controlled atmosphere stunning on the behaviour, physiology and carcase and meat quality of broiler chickens were studied experimentally in a pilot scale plant. 2. Gas mixtures tested were: single phase anoxic mixture (90% Ar in air, <2% O(2)); single phase hypercapnic anoxic mixture (60% Ar, 30% CO(2) in air, <2% O(2)); and biphasic hypercapnic hyperoxygenation mixture (anaesthetic phase, 40% CO(2), 30% O(2), 30% N(2); euthanasia phase, 80% CO(2), 5% O(2), 15% N(2)). 3. Anoxic stunning resulted in the least respiratory disruption, mandibulation and motionlessness, but most head shaking, leg paddling and twitching. Loss of posture occurred soonest with hypercapnic anoxia with the earliest and most twitching and wing flapping in individuals and earliest leg paddling. Biphasic birds were most alert, exhibited most respiratory disruption and mandibulation, and had the latest loss of posture and fewest, but longest bouts of wing flapping and least leg paddling and twitching. 4. Significant and sudden bradycardia and arrhythmia were evident with all gas mixtures and were not related solely to anoxia or hypercapnia. Birds stunned by Ar anoxia showed a slightly more gradual decline from baseline rates, compared with hypercapnic mixtures. 5. Few differences were found between gas mixes in terms of carcase and meat quality. Initial bleeding rate was slowest in biphasic-stunned birds, but total blood loss was not affected. Acceleration of post-mortem metabolism in anoxic-stunned birds was not sufficient to allow de-boning within 5 h without the risk of tough meat. 6. On welfare grounds and taking into account other laboratory and field studies, a biphasic method (using consecutive phases of anaesthesia and euthanasia) of controlled atmosphere stunning of broilers is potentially more humane than anoxic or hypercapnic anoxic methods using argon or nitrogen.     

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 and gaseous stunning on the carcase and meat quality of broilers

1. The aim of the experiment was to investigate the effect of gaseous stunning methods on the carcase and meat quality of broilers (dead weight 1.0 to 2.3 kg) in comparison with electrical stunning.

2. Two replicates of broilers (age 54 and 59 d respectively) were stunned in carbon dioxide, in argon or by electric current, and the carcases were plucked either by a mechanical plucker or by hand.

3. Carcase and meat quality were evaluated to determine the effect of these stunning treatments and plucking methods. The quality factors measured included pH at 20 min post‐mortem, ultimate pH, texture and colour of the pectoralis major muscle, and the incidence of carcase appearance defects, cooking loss, broken bones and bruises in the breast and leg muscles.

4. Stunning method had a significant effect on pH at 20 min, ultimate pH, texture and colour of breast meat. Plucking method had a significant effect on the cooking loss and texture.

5. Argon stunning resulted in fewer muscle haemorrhages, a more rapid early post‐mortem fall in pH and more tender breast meat than in the electrically stunned broilers; carbon dioxide stunned broilers had intermediate values for pH decline and meat tenderness but were not significantly different from argon stunning regarding muscle haemorrhages.

6. Appearance defects occurred to a similar extent in all the stunning methods and mechanical plucking resulted in 4 times as many defects compared with hand plucking; the incidence of broken bones was higher in mechanically plucked broilers than in hand plucked carcases.

7. Gaseous stunning of broilers produced relatively better quality carcases and meat than electrical stunning, and therefore may have commercial advantages.     

Effect of electrical stunning frequency on ventricular fibrillation, downgrading and broken bones in broilers, hens and quails

The effect of stunning current frequency on the incidence of ventricular fibrillation was determined in broilers and hens. When a pulsed unipolar square wave (DC) was used the incidence of ventricular fibrillation decreased as the frequency was increased beyond 125 Hz. When a sinusoidal AC was used, 50 Hz killed some of the birds whereas at the corresponding r.m.s. currents no birds experienced a ventricular fibrillation with 1500 Hz. In quail, it was found that between 45 and 110 mA (50 Hz) all birds experienced a ventricular fibrillation. The effect of 50, 200 and 350 Hz square wave DC on carcass downgrading was examined in broilers, and there were no differences between the groups. It was concluded that there were few advantages from using high frequency stunning currents in poultry.     

Prediction of carcase and breast weights and yields in broiler chickens using breast volume determined in vivo by real-time ultrasonic measurement

1. The use of in vivo real-time ultrasonic (RTU) to predict breast and carcase weights and yields in 103 male broiler chickens was evaluated. Breast area (mm(2)), thickness (mm) and volume (cm(3)) were measured by RTU in three identified sites. After RTU measurements, the broiler chickens were weighed (live weight, LW, g) and slaughtered Carcase and breast weights (g) and physical measures of breast area (mm(2)), and thickness (mm) corresponding to the three identified sites, and volume (cm(3)) were recorded. 2. The best simple correlation between RTU and carcase measurements was obtained for breast volume. Breast and carcase weights were well predicted by LW. Furthermore, breast volume measured in carcase or by RTU was better in predicting breast weight and breast and carcase yields. 3. Multiple regression equations were fitted using LW (g) and RTU measurement of breast volume to predict breast and carcase weights and yields. The coefficients of determination were 0.52 and 0.65 for breast and carcase yields, respectively, and 0.92 and 0.99 for breast and carcase weights, respectively.     

Effect of ventricular fibrillation at stunning and ineffective bleeding on carcase quality defects in broiler chickens

1. This experiment was concerned with whether ineffective bleeding could exacerbate the incidence of haemorrhagic conditions in broiler carcases, when ventricular fibrillation (VF) was induced at stunning.

2. Broiler chickens were electrically stunned with 81 mA per bird and then allocated to three treatments. About 67% experienced a VF at stunning and half of these birds were bled out before processing while the other half were processed without being bled out. The birds which did not experience a VF at stunning were bled out before being processed. The carcases were subjectively graded for haemorrhagic conditions.

3. Inducing a VF at stunning caused increases in the incidence of red wingtips and haemorrhaging at the humerus‐radius joint in the birds which were bled out. There were no other obvious effects of inducing a VF on carcase downgrading.

4. Failure to bleed the chickens which had a VF at stunning resulted in high incidences of red wingtips, red necks, haemorrhaging at the humerus‐radius joint and red sternal feather tracts. It was concluded that bleeding efficiency was important in influencing the expression of these characteristics when a VF occurred at stunning.     

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.     

Carcase and meat quality in broilers either killed with a gas mixture or stunned with an electric current under commercial processing conditions

1. Carcase and meat quality were evaluated under commercial conditions in 400 broilers either killed with a mixture of 30% carbon dioxide and 60% argon in air or stunned with a 50 Hz AC with clipped sine wave.

2. Compared with electrical stunning, killing broilers with the gas mixture eliminated or substantially reduced the prevalence of carcase and meat quality defects.

3. The results also showed that killing broilers with a mixture of 30% carbon dioxide and 60% argon would enable filleting (deboning) to be performed at 4 h post mortem without adversely affecting the cook loss or texture of breast meat.     

Broken bones in chickens: Effect of stunning and processing in broilers

1. Broilers and broiler carcases, sampled immediately before the stunner, at the end of the processing line and from a supermarket company, were physically dissected to determine the incidence of broken bones.

2. Over 95% of the frozen broilers from the supermarket company had broken bones and there were between 3 and 4 breaks per carcase. Only 3% of live birds had broken bones so most of the carcase damage must have been caused by processing.

3. The effect of 100, 200 and 300 V electrical stunning on the incidence of broken bones was investigated: increasing voltage resulted in an increase in the incidence of broken bones in the collar region.