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.     

Effectiveness of electrical stunning applied using a variety of waveform-frequencycombinations and consequences for carcase quality in broiler chickens

1. The effectiveness of electrical stunning of poultry was assessed where the recommended current of 105 mA per bird was applied using a range of waveform-frequency combinations. In addition the effect of the treatments on subsequent carcase quality was investigated. 2. The use of frequencies greater than 50 Hz was associated with a failure to induce ventricular fibrillation. 3. All waveform-frequency combinations were equally effective in producing a stunned state; the time to recovery was not affected by stunning treatment but was significantly longer in heavier birds. 4. The use of high frequency (500 Hz and 1500 Hz) stunning currents resulted in a decrease in carcase downgrading and a marked reduction in the occurrence of breast muscle haemorrhages, which represent significant commercial benefits to be gained by their use.     

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.     

Contamination of the bovine streak canal during mechanical milking

A newly recognised problem of petechial haemorrhages in external adipose tissue of lambs was investigated at a meat works. The causal factor was electrical stunning, but animal- associated predisposing factors were also important as indicated by a decline in prevalence as the killing season progressed. It is suggested that these are associated with the age of the lambs and, thereby, the maturity of tissues. Histologically, the lesions showed focal capillary haemorrhage, platelet and fibrin thrombi, and concentration of leucocytes about the thrombus. Although this distribution superficially resembled a reactive change, it was concluded that it was an agonal lesion and suggested that the concentration of leucocytes was a result of a filtration phenomenon.     

Broken bones in domestic fowl: handling and processing damage in end-of-lay battery hens

1. 3115 end-of-lay battery hens and carcases were sampled at set points in the sequence of events that occurred between depopulation of the battery cages at the layer farms and the end of the evisceration line in two processing plants. Live birds were killed in a convulsion-free manner and carcases were dissected to determine the incidence of broken bones. 2. Of the live battery birds 29% had broken bones by the time they reached the waterbath stunner, with on average 0.5 broken bones per bird. Removing birds from the battery cages and hanging them on the slaughter line were identified as causes of broken bones. 3. By the time birds left the end of the eviscerating line, 98% of carcases had broken bones, with on average 6 broken bones each. The stunning, plucking and eviscerating processes caused most of this damage. In particular, stunning broke the furculum, coracoid and scapula, plucking broke the ischium, pubis and ribs, and evisceration damaged the ischium and pubis.     

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.     

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.     

Killing of cattle via electrical stunning

For disease control in the case of epidemics killing of cattle via electrical stunning is a method of choice. The official veterinarian is responsible for monitoring the adhesion to animal welfare principles during electrical stunning and killing.This requires specialised knowledge and experience as the symptoms of effective stunning are quite variable in cattle. Signs of effective and ineffective stunning are described below. In addition to suitable technical equipment, restraint of the animals and correct use of the equipment, neurophysiological processes have to be considered. Calm handling of the animals avoiding stress is a prerequisite for ensuring animal welfare and minimising pain especially when killing cattle using electrical methods.     

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.     

The use of electrical stunning followed by electro-immobilization for the humane slaughter of cattle

Sir;- In New Zealand, calves are often electrically stunned before slaughter. However, electrical stunning is not usually used for adult cattle, primarily because the large size of the adult animal makes restraint more difficult, resulting in less reproducible stunning, with potential danger to personnel from animal movement. In addition, the slaughter of cattle may be inhumane if the stunning process does not ensure immediate and permanent insensibility (Newhook and Blackmore 1982b). The use and humaneness of electrical stunning of sheep and cattle have been the subject of our recent research, in which we have addressed and resolved many of these problems. We wish to relate our observations in the context of head-only electrical stunning of cattle followed by electro-immobilization to maintain insensibility and ensure carcass stillness.     

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.     

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.     

CO2 stunning of broilers and turkey hens

Stunning of poultry is still not solved satisfactorily. This concerns the requirements of animal welfare, meat quality and working conditions in the lairage, stunning and debleeding area. In an investigation of combined CO2-/O2-stunning in a new gas stunning system stress reactions of the animals during the induction phase and stunning effectivity were recorded in 7,000 chicken and 3.825 turkeys. During the induction phase (here: chicken 41 sek./turkeys 25-65 sec.) the animals first staid calm and then showed beak-opening as a consequence of the breathing stimulating effect of CO2. As a further sign of the aversiveness against CO2 the animals showed head shaking and wing flapping. The used settings of gas concentrations and stunning time in the system investigated lead to a very deep stunning resp. Killing of the animals. Therefore the debleeding cut could be performed late (chicken 44-55 sec., turkeys 54-90 sec.) after leaving the system without animals regaining consciousness. The stunning of turkeys with a mixture of CO2 and oxygen is an improvement according to animal welfare requirements because unnecessary pain and suffering, happening very often with electrical stunning, can be avoided. As far as animal welfare in chicken stunning is concerned it must be evaluated if gas stunning means an improvement because stress during the till now relatively long induction phase must be put into relation with comparably lower stress caused by hanging upside down and a fast and safe working electrical stunning unit.     

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.     

Electrical stunning of cattle--experiences in New Zealand

Ever since the middle of the nineteen-eighties electrical stunning of cattle is used in industrial slaughter plants in New Zealand. Today electrical stun boxes operate in export slaughter plants throughout New Zealand. The reversible stun is utilised on the vast majority of slaughtered cattle. The electrical stunning (head only) immediately followed by bleeding is an alternative to ritual slaughter without prior stunning. Throughout the world's islamic community this alternative is widely accepted as Halal.     

Observations of subcutaneous haemorrhagic speckling in lambs

A survey carried out at a meat export works in the southern part of the North Island indicated that 29% of lambs killed during the early part of the 1978/79 season had lesions de- scribed as subcutaneous haemorrhagic speckling. In 2.6% of lambs, the lesions were sufficiently severe to warrant downgrading.

Investigation indicated that the primary factor associated with “speckling” in subcutaneous fat was related to electrical stunning by a triple electrode stunner. The lesions were more noticeable in lambs with a thinner layer of carcass fat (Y-grade lambs); other factors such as age, dampness of fleece and stunning technique may also have been associated with their prevalence. It is suggested that, by suitably designed studies, some of these variables could be controlled and their effect assessed.     

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.     

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.     

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.     

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.