Effects of electrical and mechanical stunning methods on meat quality in ostriches

The effect of electrical and captive needle air pressure stunning methods on some meat quality parameters was examined in ostriches under practical conditions. One hundred and fifteen ostriches were used in three experiments. The ostriches were stunned either electrically (head only) or by using a captive needle with air pressure. In the first experiment the ostriches were stunned at 90 V (～effectively 52 V), 200 V and by captive needle using air pressure. In the second experiment voltages of 175 and 200 V were applied and a captive needle stunning method using air pressure. In the third experiment the birds were stunned at 175 V with a short stun/stick interval. Experiments 2 and 3 were performed in a different slaughterhouse from experiment 1. Meat quality was assessed by measuring the pH, temperature and colour at 45 min and 18 h post mortem and by determining water binding capacity and haemorrhage score at 18 h post mortem in the big drum, tender loin and triangular filet muscles. The measured stunning parameters in the first experiment were 204±96 mA (～52 V) during 11±1 s and 556±85 mA (～200 V) during 6±0 s. The stun/stick interval was 136±38 s. The rigor mortis value in the tender loin and both pH(1) and pH(2) in the big drum, tender loin and triangular filet muscles were (p<0.05) lower when stunned with air pressure compared with electrical stunning. Moreover internal light scattering remained higher. The measured currents in the second experiment were 561±226 mA (～173 V) during 6±2 s and 518±120 mA (～200 V) during 6 s. The stun/stick interval was 39±12 s. The pH at 45 min and 18 h differed (p<0.05) in the tender loin and triangular filet muscles as did the temperature at 45 min in the three muscles between the different stunning groups. The stunning in the third experiment was carried out with 548±180 mA during 6±2 s. The stun/stick interval was 5±2 s. After the short stun/stick interval the pH(2) was lower (p<0.05) for the tender loin and triangular filet muscles and the wetness of the filter paper of the big drum was (p<0.05) lower compared with the other groups. Our experiments showed that stunning methods affected several meat quality parameters. Using a high electrical stunning current, captive needle stunning or a short stun/stick interval may positively affect some parameters. More research is necessary to examine effects of pre slaughter handling on meat quality.     

The effect of electrical stunning and slaughter on the electroencephalogram of sheep and calves

To study the application of electroencephalography (EEG) for the assessment of insensibility during stunning and slaughter, recordings were made on sheep that were slaughtered by throat cutting, electrically stunned head-only and allowed to recover, electrically stunned head-only followed by throat cutting or electrically stunned head-to-back. The same experiments were repeated on calves (1–6 weeks old) except some calves were stunned and allowed to recover before final stunning and throat cutting.

After the throat cut, sheep became insensible (i.e. EEG < 10 μV) at 8–22 s but the calf EEG did not fall below 10 μV until 79 s after the cut. With head-only stunning/recovery, high-amplitude EEG waves (electroplectic fit) continued for 47 s (sheep) and 33 s (calves) post stun. A quiescent period followed, which then developed into a period of moderate-amplitude EEG signals, so that, at 50 s post stun, the EEG usually exceeded 50 μV and often had bursts of 150 μV activity. After head-only stunning/throat cutting, the electroplectic fit was shortened (39 s in sheep, 23 s in calves) and the EEG took at least 50 s to fall below 10 μV. With sheep stunned head-to-back, which stops the heart, and thus should cause immediate, permanent insensibility, the EEG took longer to fall below 10 μV (52 s) than after throat cutting. These results suggest that electrical stunning of sheep and calves causes a prolonged increase in the post-stun EEG amplitude. Therefore, during slaughter, stunned animals have larger amplitude EEG signals than unstunned animals, and EEG criteria developed for judging the sensibility of unstunned animals cannot be used for those that are electrically stunned.     

Electrical stunning of veal calves

A total of sixty-two calves with body weights of 200 kg and with preimplanted ECoG electrodes on the dura mater, were electrically stunned using various currents, voltages and stunning equipment. To stun 90% of the calves effectively, a current strength of 0·87 A is estimated to be necessary when using scissor model tongs. Effective stunning means immediate (within 1 s) induction of unconsciousness by a general electroplectic insult. Atrial fibrillation is a frequently occurring phenomenon after electrical stunning when the electrodes are placed between the eye and the ear. The relatively short duration of the insult in calves compared with pigs, as well as the clonic spasms occurring 10s after stunning, are major drawbacks to the practical application of electrical stunning of veal calves. The experiments show that these drawbacks can be eliminated by modifying the form and position of the electrodes.     

Electrical stunning of sheep

In seventy Texel breed sheep with a live weight of about 43 kg electrocorticogram (ECoG) electrodes were implanted in the dura mater. The day after the operation the sheep were electrically stunned with scissor model tongs on the head. Various currents and voltages were used. A current strength of 0·33 A was statistically estimated to stun 90% of the sheep effectively, which means an immediate induction of a general epileptiform insult. The duration of an insult, using 600 V, is significantly longer than using 300 V, although the shortest duration was 23 s and 22 s, respectively. In all instances a paroxysmal ventricular tachycardia was observed after stunning. In the interests of animal welfare, electrical stunning of sheep should be performed with an amperage of at least 0·5 A (160 V) and throat cutting should take place within 16 s.     

Some neural and behavioural aspects of electrical and mechanical stunning in ostriches

Different electrical and mechanical stunning procedures were studied in ostriches to determine the effectiveness of the method. Fifty-eight South-African Black ostriches were equipped with EEG electrodes and stunned with three different electrical head-only methods and with a new captive needle pistol, using air pressure. The first stunning procedure consists of two trials. In the first trial a total of 45 ostriches were stunned with a voltage of 200 V (spiked electrodes) during 1 s. Unfortunately, in 10 animals the electrodes were disconnected. A general epileptiform insult on the EEG followed by recovery was observed in 20 ostriches. Another eight animals died after recovery and five showed an iso-electric line and were dead. The total duration of the insult was 25±10 s. The measured current was 463±120 mA. In the second trial a constant current of 400 mA was administered to 13 ostriches. In one animal the electrodes were disconnected. Eight out of 12 animals showed a general epileptiform insult, two of them showed an iso-electric line and two did not show the characteristics of a general epileptiform insult. The total duration of the insult on the EEG was 21±8 s. The measured current was 365±91 mA and the voltage 191±27 V. During the second stunning procedure four and seven ostriches were stunned with 200 V (spiked electrodes) and 48 V (blunt electrodes), respectively, during approx. 6 s. They all died. In addition, a group of 20 ostriches stunned with captive needle pistol using air pressure showed unconsciousness after stunning by the appearance of theta and delta waves tending to an iso-electric line on the EEG trace. It is recommended to use at least 500 mA to stun ostriches effectively and to use a short stun-stick interval or to kill them by a long stunning duration. The captive needle pistol, using air pressure, can be an alternative for electrical head-only stunning.     

Electrical stunning by direct brain stimulation in pigs

The effects of electrical stunning of slaughter pigs by electrodes shot into the brain, on sensibility and on the incidence of haemorrhages in the shoulder postmortem, were studied.

To determine the efficiency of this method 37 slaughter pigs were equipped with EEG (electroencephalograph) and ECG (electrocardiograph) electrodes and stunned twice via the EEG electrodes. In the first experiment the pigs were stunned with 25 V and in the second with 25 V followed by a relaxation current. The day after slaughter the shoulders were scored for haemorrhages. Under more practical conditions three groups of 10 pigs each were electrically stunned via electrodes shot into the brain using 25, 50 or 75 V, followed by a relaxation current. The day after stunning the shoulders were scored for haemorrhages.

The pigs did not react to shooting electrodes frontally into the head. After stunning all animals showed a general epileptiform seizure. However, after the second stun the tonic and clonic muscle cramps were impaired. The heart rate increased significantly (P < 0·01) after stunning, and extra systolae and irregular heart rates were observed. In the shoulders of 27% of the carcasses no haemorrhages were found and in the remainder only minor haemorrhages were seen. Under practical conditions a voltage of 87(± 2) V and a current of 511(±20) mA seemed to be necessary for an effective stun. When lower voltages were applied fewer carcasses with shoulder haemorrhages were found.

It may be concluded from these experiments that 25 V (134 mA; 150 Hz) is sufficient for effective stunning of slaughter pigs when electrodes are in direct contact with the brain. But as the optimum position of the electrodes may not be reached under practical conditions a voltage of approximately 90 V (550 mA; 150 Hz) is recommended. After this stunning method only a few haemorrhages were observed in the shoulders.     

The use of a high pressure waterjet combined with electroimmobilization for the stunning of slaughter pigs: Some aspects of meat quality

It is considered that waterjet stunning may be a humane stunning method to apply in slaughter facilities. An experiment was conducted in a slaughterhouse to examine the effects of waterjet stunning combined with electroimmobilization during exsanguination on the occurrence of haemorrhages in the muscles and on meat quality.Slaughter pigs (n = 31) were stunned by waterjet (3900 bar) in a V-type restrainer and immobilized electrically (40 V) during exsanguination. Control animals (n = 39) were stunned automatically and electrically (600 V) using the same restraint device.At 45 min post mortem the pH in the semimembranosus (SM) and longissimus dorsi (LD) muscles was significantly lower (p < 0·01), while rigor mortis and temperature in the SM and LD were significantly higher (p < 0·05 and p < 0·01, respectively) in the carcasses of pigs stunned with the waterjet as compared to control pigs. At 18 h post mortem the ultimate pH of the LD was lower (p < 0·05), while scatter (fibre optic probe) and filter paper test values of the LD were higher (p < 0·01) in carcasses of pigs stunned with the waterjet. Fewer haemorrhages were observed in the shoulders of pigs stunned with the waterjet.The results of this experiment suggest that waterjet stunning, when combined with electroimmobilization, may be a suitable method to stun pigs in a slaughterhouse. However, further studies are required to improve the meat quality.     

Comparison of CO(2) stunning with manual electrical stunning (50 Hz) of pigs on carcass and meat quality

The effects of carbon dioxide stunning on carcass and pork quality attributes were compared with the effects of manual electrical stunning using either head-only or head-to-brisket electrodes. A total of 30 Large White×Landrace boars (homozygous dominant for the halothane gene) were randomly allocated immediately prior to slaughter to one of three stunning treatments: carbon dioxide (90% CO(2)), head only (HO; 1.3 A for 4 s at a frequency of 50 Hz) or head to brisket (HBR; 1.3 A for 4 s at a frequency of 50 Hz) electrical stunning. The pH of the M. longissimus thoracis (LT) muscle measured at two sites [between the fifth and sixth thoracic vertebrae (Site 1) and the last thoracic rib (Site 2)] at 40 min post-slaughter was lower (P<0.001) in HBR stunned pigs compared with both CO(2) and HO stunned pigs. No differences in ultimate pH of the LT at either measurement site were found due to stunning method. However, a faster (P<0.05) relative rate of pH decline was found in the LT at Site 1 from HBR stunned pigs compared with CO(2) stunned pigs. No difference in the relative rate of muscle pH decline (P>0.05) between stunning methods was found in the LT muscle at Site 2. Pork from HBR stunned pigs was paler (P<0.05) and had a higher (P<0.001) percentage drip loss compared with pork from HO and CO(2) stunned pigs. LT muscles from HBR stunned pigs had lower (P<0.001) WB shear force values compared with pork from HO stunned pigs (6.57 vs. 8.12 kg, S.E.D. 0.49). Carcass quality was improved by CO(2) stunning, with less (P<0.05) ecchymosis-affected pork trimmed from shoulder primals compared with electrically stunned pigs. These results indicate that manual electrical stunning of pigs using HO tongs and CO(2) stunning reduced percentage drip loss, reduced muscle lightness and reduced the rate of muscle pH decline compared with pigs manually electrically stunned using HBR tongs.     

Effect of stun duration and current level applied during head to back and head only electrical stunning of pigs on pork quality compared with pigs stunned with CO(2)

The effect of current, duration and method of application of manual electrical stunning on pork carcass and meat quality attributes in comparison with stunning pigs with CO₂ was investigated. Two experiments were conducted using a total of 96 Large White×Landrace boars (homozygous dominant for the halothane gene). In Experiment 1, 48 pigs were allocated to one of six stunning treatments: CO₂ (90% in air), electrical stunning (ES) using head only (HO) tongs delivering current at a frequency of 50 Hz at 1.3 or 2.0 A for 4 s and 0.9, 1.3 or 2.0 A for 19 s. Higher drip loss occurred in M. longissimus thoracis et lumborum (LTL) muscles from ES pigs, except those stunned with 0.9 A for 19 s, compared with pigs stunned with CO₂. The incidence of pale, soft exudative (PSE) meat was higher in ES pigs, except those stunned at 1.3 A for 4 s, compared with CO₂ stunned pigs. In Experiment 2, 48 pigs were allocated to one of six stunning treatments: ES using a head to back (HB) handpiece delivering current at 1.3 or 2.0 A for 4 s and 0.9 or 1.3 A for 10 s; HO 1.3 A for 4 s or CO₂. Although stunning treatment did not influence ultimate pH, muscle lightness, tenderness or cooking loss, drip loss and PSE incidence in LTL muscles from CO₂ stunned pigs were lower compared with ES pigs. Overall, ecchymosis and bone fractures were more prevalent in ES pigs compared with CO₂ stunned pigs. This research identified that stunning pigs with CO₂ compared with manual ES lowered the incidence of bone fractures, ecchymosis, PSE and drip loss of pork.     

Arrested blood flow during false aneurysm formation in the carotid arteries of cattle slaughtered with and without stunning

The time to onset of arrested blood flow and the size of false aneurysms in the severed carotid arteries were assessed in 126 cattle during halal slaughter without stunning. Thirty six cattle (29%) showed early arrest of blood flow. In 6%, both the left and right carotid arteries in the same animal stopped bleeding before 60 s had elapsed following the neck cut. The time to early arrested blood flow was on average 21 s, and this was accompanied by enlargement with false aneurysms which occluded the arteries. In the arteries which were still bleeding at 60 s after the neck was cut the artery size was normal. Based on comparative data from different slaughter premises it appeared that making the cut in the neck at the first cervical vertebra instead of the second to fourth cervical vertebrae reduced the frequency of false aneurysm formation and early arrested blood flow. This was confirmed in a separate controlled trial where 100 cattle were stunned with a captive bolt and the arteries were examined following neck cutting at either the C1 or C3 positions.     

Relationships between time of stunning and time of throat cutting and their effect on blood pressure and blood splash in lambs

A study based on 84 electrically stunned lambs showed that those gash stuck (transverse incision of the extended neck which almost simultaneously severs the trachea, oesophagus, common carotid arteries and jugular veins and the spinal cord at the occipito-atlantal junction; Blackmore & Newhook, 1976) immediately after removal of the electrical applicator had a lower incidence of blood splash than lambs gash stuck 5-8 sec r stunning. Lambs whose throats were cut immediately before the application of the electrical current had the lowest incidence of blood splash. None of the splash observed was of commercial significance. Systolic blood pressure recordings were made on a further 12 lambs of a similar age, 10 of which were electrically stunned and two shot with a captive bolt pistol. Blood pressure changes observed were related to the blood splash results obtained in the first trial. Electrical stunning raised blood pressures to an average of 3·5 times normal in lambs allowed to recover from stunning. A further seven young unweaned lambs which were electrically or percussion stunned showed a similar pattern of blood pressure change to that reported for older lambs following stunning, except that lower maximum pressures were reached. The authors interpret the results of the present trials as indicating that the application of electrical current to the heads of lambs results in damage to small vessels prior to the elevation of blood pressure. This damage may become apparent in the dressed carcass and organs as small haemorrhages. The subsequent rise in blood pressure following stunning then exacerbates the leakage of blood into tissues and it becomes more apparent in the form of discrete haemorrhages or blood splash.     

The effects of electrical stunning and percussive captive bolt stunning on meat quality of cattle processed by Turkish slaughter procedures

The effects of electrical and percussive captive bolt stunning both on initial and up to 14 days post mortem meat quality of Friesian young bulls were studied. The first group (NS; n=10) were slaughtered without stunning under Turkish slaughter procedure (these animals were slaughtered under conditions acceptable to the appropriate ethics committee) in a modern abattoir. In the second group (ES; n=10) animals were electrically stunned. In the third group (PS; n=10) animals were stunned with percussive captive bolt. Meat quality was assessed by examining muscle glycogen concentration, pH and WHC. Also cooking loss, texture parameters and consumer sensory properties were assessed at 24 h, 4, 7 and 14 days post mortem. Meat colour as L^*, a^*, b^*, C^*, h^* values were evaluated at 0, 48 h, 3, 5, 7, 9 and 14 days post mortem. Pre-slaughter handling affected muscle glycogen concentration (P<0.05). Animals in electrical and percussive captive bolt stunned groups had higher muscle glycogen concentrations compared to animals in the non-stunned group (P<0.05). Although pre-slaughter handling did not affect significantly pH_{24 h} and WHC, differences were significant for cooking loss, colour coordinates and texture parameters at some storage times. For all sensory attributes (odour, flavour, tenderness and overall acceptability) at all ageing periods (24 h, 4, 7 and 14 days) the percussive stunned (PS) group was significantly superior to the non-stunned (NS) group. The electrically-stunned (ES) group also tended to be superior to the NS group although not all differences were statistically significant. These results indicate that percussive captive bolt stunning of cattle improved meat quality compared with cattle electrically stunned using head only tongs and those non stunned under approved Turkish slaughter procedure.     

The effect of repeat application of electrical stunning on the welfare of pigs

Although legislation requires the production of immediate insensibility, implying that a stun can be applied only once, the practice of repeat application of electrical stunning is common. However, the relative consequences of such repeat applications are unknown. This study investigated the effects of repeat applications of electrical stunning (200 V, 50 Hz) following different delays of 15, 60 or 180 s between the initial stun and the repeat applications. The parameters examined, following stunning, were the durations of spontaneous physical activity, time to return of reflexes and the duration of the epileptiform activity in the electrocorticogram. The results showed that repeat application of electrical stunning can produce successive epileptic activity and therefore an effective stun. The duration of tonic and clonic phase activity following repeat application was significantly shorter than after a single stun only. There was a tendency for the reflexes to return more quickly following repeat application. The use of electrical stunning to re-stun pigs appears to raise no welfare concerns and although commonly used, should only be applied out of necessity rather than as routine practice.     

Blood in the respiratory tract during slaughter with and without stunning in cattle

Bovine respiratory tracts were examined for blood following shechita without stunning, halal slaughter without stunning, and captive bolt stunning with sticking. In all three methods the cattle were in the upright (standing) position at the start of bleeding. Those that had not been stunned continued to breathe during the early part of bleeding whilst those that were stunned were not breathing. Nineteen percent of the shechita, 58% of the halal and 21% of the stunned plus stuck cattle had blood lining the inner aspect of the trachea. Thirty six percent, 69% and 31% had blood in the upper bronchi, respectively. Ten percent, 19% and 0% had fine bright red blood-tinged foam in the trachea, respectively. It was concluded that concerns about suffering from airway irritation by blood could apply in animals that are either not stunned before slaughter or do not lose consciousness rapidly whilst blood is present in the respiratory tract.     

Rate of blood loss and timing of exsanguination on prevalence of ecchymosis in fallow deer (Dama dama)

Blood loss associated with four combinations of stunning and exsanguination methods was determined as part of studying prevalence of ecchymosis in slaughtered fallow deer (Dama dama). A fifth treatment simulated incomplete severance of the extended neck after captive bolt stunning. Predicted mean weights of blood collected from the five slaughter treatments, including electrical stunning followed by the thoracic stick method of exsanguination, captive bolt stunning followed by the thoracic stick, captive bolt stunning followed by the gash cut method of exsanguination, electrical stunning followed by the gash cut, and captive bolt stunning followed by incomplete severance of the extended neck, were 1458.7, 1072.7, 684.5, 463.7, and 228.5 g, respectively. The overall effect of exsanguination method was highly significant (p < 0.001) with the thoracic stick resulting in the greatest weight of blood collection in the 10 s period immediately after initiation. The overall effect of stunning method on blood loss was not significant, although there was a significant (p < 0.05) stunning method by exsanguination method interaction. Ecchymosis of varying severity occurred in some carcases from all treatment groups. Using the total loin and round ecchymosis scores, when little or no ecchymosis (grades 0 or 1) was compared with some ecchymosis (?grade 2) by logistic regression, castrated bucks were 9.8 times more likely (p = 0.002) and does 4.2 times more likely (p = 0.06) to have some ecchymosis than entire bucks. The results indicate that ecchymosis can be reduced in fallow deer carcases by thoracic stick exsanguination incorporated less than 10 s after stunning.     

Physiological responses of Manchega suckling lambs: Effect of stunning with different CO2 concentrations and exposure times

Four groups of Manchega breed suckling lambs, stunned with different CO₂ concentrations and exposure times (G1: 80% CO₂ 90 s; G2: 90% CO₂ 90 s; G3: 90% CO₂ 60 s; G4: 80% CO₂ 60 s) plus an electrically stunned control group (G5), were used to determine (1) the physiological responses (hormonal, haematological and biochemical blood parameters) of animals after stunning and (2) the stunning effectiveness in each group. No significant differences were found among groups for hormonal levels. Within haematological parameters, significant differences among groups were only found for haemoglobin (P < 0.05) and leucocytes (P < 0.01), with lowest values in both groups stunned with 90% CO₂. There were significant differences between groups (P < 0.01) for urea and total protein, creatinine and LDH (P < 0.05; lowest and highest, respectively, for G1) and for sodium (P < 0.001; lowest in G3). Stunning effectiveness was highest in G5, G3 and G1 groups and lowest in G2 and G4 (100%, 90%, 89%, 50% and 43%, respectively). According to discriminant analysis, sodium, leucocytes and creatinine marked the differences among stunning groups.     

Electrical stunning and stillness of lambs

The stillness obtained with head-to-back stunning results from the current depolarizing spinal neurones. The same effect can be achieved by sequentially applying a head stun, followed by a current through the heart to stop it and a current down the spinal cord to abolish movement. The level of speckle bruising for this sequential stun is lower than that associated with head-to-back stunning and is similar to that of head-to-foreleg stunning. After head-only stunning, current passed continuously down the spinal cord through a good contact at voltages around 40 V gave adequate stillness, which improved when the voltage was raised to 80 V. With a frequency of 14 Hz, 40 V presented no hazard to workers. After head-only stunning, a brief application of current down the entire spinal cord for 2-4 s at 110 V or greater also effectively suppressed movement. With legs as contact points voltages as high as 400 V were necessary. For effective animal stillness good electrode contact is necessary and electrodes should be placed as close to the spinal cord as possible. With a continuous current flowing the oesophagus remained closed until muscle exhaustion occurred; even with a brief current down the spinal cord, the oesophagus remained closed for at least 30 s. Low voltage stimulation in the form of a continuous current cannot replace high voltage stimulation, but can supplement it, and therefore could be incorporated into the electrical stimulation process. Head-only stunning, followed by a cut through the major blood vessels of the neck, is acceptable for Halal slaughter and is now in use commercially in New Zealand. Subsequent movement is suppressed by a spinal discharge at 400 V using leg contacts.     

Studies on the return of physical reflexes in pigs following electrical stunning

In order to obtain quantitative information on the duration of insensibility in pigs (60-80 kg) following electrical stunning, experiments were carried out using 50 Hz alternating current for 3 and 7 s current durations at different voltages. The following features were examined: the mean current received by each pig, the period of loss of reflexes and the time to return of spontaneous activity, and cranial nerve reflexes. In particular the return of breathing was used as a first sign of recovery, and the response to a nose prick and presence of the righting reflex were used as indicators of overt consciousness. A minimum current in excess of 406 mA was required to effectively stun these pigs with sufficient duration of loss of reflexes. At least 150 V for 3 s current duration should be used and a maximum stunning to exsanguination interval of 15 s is considered sufficient to ensure pigs of this size do not regain consciousness following the stun.     

Systems stunning with CO2 gas on Manchego light lambs: Physiologic responses and stunning effectiveness

Effect of four stunning treatments using different CO₂ concentrations and exposure times (G1: 80%90 s; G2: 90%90 s; G3: 90%60 s; G4: 80%60 s) on hormonal, haematological and biochemical parameters in Manchego breed light lambs and their stunning effectiveness (% animals correctly stunned) was studied. An electrically stunned control treatment (G5) was used. G1 showed the highest plasmatic hormonal, red cell distribution (RDW) and lactate levels. Haemoglobin, mean corpuscular volume (MCV), mean cell haemoglobin (HbCM), glucose, lactate deshydrogenase (LDH), sodium, potassium and creatine kinase (CK) were highest in G5. Stunning effectiveness was maximum (100%) in G3 and G5, only 50% in G1 and G2 and minimum (30%) in G4.     

The effect of electrical head-only stun duration on electroencephalographic-measured seizure and brain amino acid neurotransmitter release

Effective electrical head-only stunning produces a seizure-like state followed by a period of analgesia seen in animals allowed to recover. Passing of a 1·0 A current (50 Hz, 500 V) for less than 0·2 s, through the head of a sheep does not produce a seizure-like state as evidenced by recorded electroencephalogram. Corresponding to this lack of seizure-like state, the release of the neurotransmitters glutamate and aspartate, in the brain, occurs to levels associated with arousal rather than seizure. At a duration of 0·2 s, the same stun parameters as above produce a seizure-like state and the release of glutamate and aspartate rises dramatically. The length of the seizure-like state, and the levels of release of glutamate, aspartate and a third neurotransmitter gamma amino-4-butyric acid (GABA), increased with stun duration until 4·0 s duration, where a peak in these parameters was seen. Stun durations of 2·0, 4·0, 8·0 and 12·0 s all produce similar effects. At a duration of 20 s, however, the length of the seizure-like state and the release of neurotransmitters is less than at shorter stun durations. For welfare purposes a head-only electrical stun, of 1·0 A, at a duration as low as 0·2 s produces unconsciousness and analgesia to subsequent slaughter procedures. However, maximum welfare benefits appear attainable at durations between 2·0 and 20·0 s.