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.     

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 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.     

The influence of slaughter method on the residual blood content of meat

The effect of slaughter method on the residual haemoglobin content of the M. longissimus dorsi and the amount of blood lost at exsanguination of sheep was investigated. The influence of stunning method (electrical, 90 V, or captive bolt pistol), pithing and bleeding-out position were examined. Sheep bled lying lost more blood than those bled hanging and electrically-stunned animals lost more blood than those stunned with a captive bolt pistol; pithing had no effect. The residual haemoglobin content of the muscle did not vary significantly between methods and there was no relationship between it and the amount of blood lost at slaughter.     

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.     

Effect of electrical stunning on meat and carcass quality in lambs

The effect on meat quality and the presence of haemorrhages were assessed in head-only electrically stunned and non-stunned lambs. Colour (L?, a?, b?), muscle ultimate pH (pHu), chilling losses and carcass weight at 45 min and 24 h were not significantly different between treatments. However, the amount of blood lost relative to live body weight and the killing-out were significantly higher (P<0.05) in electrically stunned lambs compared with non-stunned lambs. No carcasses with petechiae, ecchymosis, haematomas and bone fractures were found in either treatment. On the other hand, the incidence of hearts with petechiae was significantly (P<0.05) higher in electrically stunned lambs compared with lambs slaughtered without prior stunning. It is concluded that meat quality and the incidence of haemorrhages are unaffected by head-only electrical stunning for 3 s at a constant voltage of 250 V.     

Post mortem energy metabolism and meat quality of porcine M. longissimus dorsi as influenced by stunning method - A (31)P NMR spectroscopic study

Post mortem changes in phosphorus metabolites and pH were studied in M. longissimus dorsi from pigs (n=10) stunned either by CO(2) (n=3), electrical (n=2), captive bolt pistol (n=2) or by anesthesia (ketamine) (n=3). (31)P-NMR spectroscopy revealed significant effects of stunning method on changes of the various phosphorus metabolites in the muscle post mortem, with the effect being most pronounced on the degradation of phosphocreatine (PCr). Moreover, the four stunning methods gave rise to large differences in the progress of pH as determined by (31)P-NMR spectroscopy. Using anesthesia as the reference showed that the captive bolt pistol caused the highest rates of post mortem degradation of phosphorus metabolites, electrical stunning intermediate, and CO(2)-stunning causing the lowest post mortem degradation rates, even though CO(2)-stunning also was associated with higher post mortem degradation rates compared with anesthesia. Finally, it was demonstrated that the water-holding capacity (WHC) of the meat was affected by the applied stunning method, as CO(2)-stunning, electrical stunning and captive bolt pistol resulted in mean drip losses of 6.4, 8.3 and 8.6%, respectively (P=0.02). The result displays the significance of induction and progress in post mortem changes on WHC in meat.     

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.     

Electroencephalographic studies of stunning and slaughter of sheep and calves- Part 3: The duration of insensibility induced by electrical stunning in sheep and calves

The duration of insensibility produced by electrical and percussive stunning was studied in sheep and calves. Insensibility was determined from the study of electroencephalograms (EEG) and concurrent observations were made of the reflexes and reactions of the animals. The effect of stunning on the circulation was assessed from electrocardiograms (ECG) and femoral blood pressures (BP). Electrical stunning of sheep by electrodes to the head only produced a period of reversible insensibility of 18-42s. This technique also caused an immediate and prolonged increase in BP. Electrical stunning of both sheep and calves by a 'head to back' method, which causes concurrent cardiac dysfunction, produced immediate and permanent insensibility associated with cessation of circulation and an immediate drop in BP. The use of a non-penetrative method of percussion stunning caused immediate insensibility and an increase in BP which persisted after exsanguination had commenced. Calves stunned with a penetrating captive bolt showed immediate and permanent insensibility and the EEG became isoelectric within 15 s.     

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.     

A comparison of the effects of electrical, captive bolt or percussion stunning on the incidence of blood splash in lambs

Three-hundred-and-three lambs were divided into three equal groups. Half the lambs in each group were not weaned before slaughter and the weaned half were slaughtered a week later. Lambs in one group were head stunned electrically before slaughter; in the second group lambs were stunned with a captive bolt pistol and in the third group they were percussion stunned before slaughter. Carcasses, gall-bladders, hearts and duodenums were inspected for blood splash after slaughter. A few small haemorrhages were detected in 57% of the electrically stunned lambs, in 30% of the captive bolt stunned lambs and in only 16% of the percussion stunned animals. Although no splash of commercial significance was found in any carcass, 25% of the electrically stunned lambs had detectably splashed carcasses, whilst only 1% of percussion-stunned lambs had splashed carcasses with captive bolt stunned lambs being intermediate in carcass splash incidence. These results show that stunning method affects the incidence of blood splash.     

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.     

致昏电压对兔肉品质的影响研究

采用100、75、65、55V和人工致昏(对照组)的宰杀方式,研究其对兔肉品质的影响,结果表明:不同致昏电压对兔肉pH值的影响差异不显著(p>0.05),只有75V致昏组与100V致昏组间宰后1h的背最长肌pH值差异显著(p<0.05);宰后1h,不同致昏电压对兔背最长肌的肉色亮度L*值、红度a*值、黄度b*值和后腿肉的L*值、a*值的影响差异不显著(p>0.05);宰后24h,75V致昏组的肌肉颜色鲜红,而人工致昏组和100V致昏组的肌肉颜色较苍白;100V致昏组的滴水损失最大,为3.738%,而75V致昏组的最小,为2.420%;蒸煮损失最大的为100V致昏组,最小的为55V致昏组,其次是75V组;肌肉嫩度最好的是75V致昏组,最差的是人工致昏组。     

Vasopressin and oxytocin in plasma of veal calves, sheep and pigs after high voltage electrical stunning

The levels of vasopressin and oxytocin in the plasma of veal calves, sheep and pigs were determined during and after a general epileptiform insult induced by high voltage stunning. Immediately after stunning, a sharp increase in the vasopressin and oxytocin levels was observed in the plasma, followed by a gradual decrease during the next hour. The duration of the general epileptiform insult was correlated (r = 0·79) with the highest measured levels of vasopressin after electrical stunning in the pigs (p ≤ 0·05). It is suggested that secretion of these neurohypophyseal hormones may affect the memory of aversive experiences during a general epileptiform insult.     

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.     

The effect of stunning method on the incidence of PSE meat and haemorrhages in pork carcasses

Two commercial pig abattoirs (A and B) equipped with a head-only and head-to-chest electrical stunning systems, and two (C and D) equipped with compact carbon dioxide (CO(2)) stunning systems, were visited during 3 days to evaluate the effects of the stunning system on meat quality and haemorrhages. Meat quality was evaluated by measuring muscle electrical conductivity (PQM) and colour (Minolta Chromameter) at 2 and 7 h post mortem (abattoirs A and C, and B and D, respectively). PQM and colour were measured in 2486 and 2321 loins respectively. Also ultimate pH (pHu) was measured in 2395 loins at 24 h post mortem. Haemorrhages were evaluated by recording the incidence of petechiae, ecchymosis and haematomas, bone fractures were also recorded. A total of 1980 shoulders, 3943 loins, and 5438 hams were inspected. In the abattoirs equipped with the electrical stunning systems, a higher (P<0.05) incidence of potentially PSE meat (PQM>6) was found compared with the abattoirs equipped with CO(2) stunning. Likewise, the loins from electrically stunned pigs were paler than those from CO(2) stunned pigs (P<0.05). Electrical stunning increased the incidence of petechiae in the loin and the ham (P<0.05). No shoulder, loin or ham with bone fractures was found in the abattoirs studied. Therefore, CO(2) stunning reduces the incidence of PSE meat and of petechiae on muscle fascia of loins and hams, compared with electrical stunning. However, petechiae are not of great importance because they can be removed from the affected commercial cuts.     

The efficacy of pulsed ultrahigh current for the stunning of cattle prior to slaughter

We present results from the development of a new system of reversible electrical stunning of cattle. A single-pulse ultra-high current (SPUC) was generated from a capacitance discharge current spike of at least 5000 V at 70 A, for approximately 50 ms. Ninety-seven cattle were stunned in three experimental protocols. With improvements made to the design of the stun box and charge delivered, 38 cattle were either stunned and immediately jugulated or monitored for signs of reappearance of brain stem reflexes at which point a concussion stun was administered. This use of the SPUC charge, provided as a biphasic-pulse waveform, resulted in a high level of stunning efficacy, with unconsciousness lasting for up to 4 min. These results were supported by EEG data taken from a subsequent cohort of stunned cattle. The SPUC stun also apparently eliminated post-stun grand mal seizures that can occur following short-acting conventional electrical stun, with its associated negative consequences on operator safety and meat quality.     

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.     

Some aspects of the effectiveness of stunning in sheep by the captive bolt

The effects of penetration depth and the velocity of the bolt on the onset of unconsciousness was investigated in twenty-four sheep of about 45 kg liveweight. The sheeps' state of consciousness was judged from the electrocorticograms recorded via electrodes surgically pre-implanted frontally on the right side of the head. Sixteen sheep were trephined. A commercial captive bolt pistol and an experimental manual bolt, both with variable penetration depths, were used to represent high and low velocity stunning. Stunning by destroying only the cortex or by only penetrating the skull when the experimental bolt or captive bolt pistol, respectively, were used, did not produce unconsciousness. Unconsciousness was obtained after destroying the cortex and deeper parts of the brain with the experimental bolt (low velocity) or after destroying the cortex (and deeper parts of the brain by shockwaves) when using a captive bolt pistol (high velocity). To produce unconsciousness the captive bolt should have sufficient energy and length after penetration of the skull to crush the cortex and deeper parts of the brain, either directly or by shockwaves.     

Effect of electrical stunning methods on petechial haemorrhages and on the blood pressure of lambs

Electrical stunning of lambs to render them unconscious and insensible to pain can result in blood splash (spots of blood in muscles) or speckle (petechial haemorrhages in fat or connective tissue overlying the muscle). Stunning through electrodes applied to the head causes mainly blood splash with some speckle, while currents applied head-to-back or head-to-foreleg can produce speckle without blood splash. To identify the causes of speckle, animal movement and blood pressure changes that occur during stunning were measured. Three different stunning methods were employed: head-only, head-to-back and head-to-foreleg. Head-only stunning, which does not stop the heart and produces a moderate amount of speckling, was accompanied by elevated arterial blood pressures up to 300 mm Hg, and venous pressures up to 100 mm Hg. The carcass became rigid on stunning but reflex kicking occurred when the hind legs were shackled. Head-to-back stunning, which stops the heart, produced a momentary arterial and venous blood pressure rise during the stun, as a result of thoracic pressure changes, followed by a decline in pressure to 40-50 mm Hg. The muscles became markedly rigid due to direct stimulation of the loin and spontaneous kicking was absent following current switch off, although spontaneous coughing persisted. Stillness associated with head-to-back stunning was accompanied by the highest incidence and severity of speckling, whereas head-to-foreleg stunning, which also stops the heart, resulted in less muscle contraction and was accompanied by the least incidence and severity of speckling. Kicking was also eliminated if sufficiently high currents were used. Stopping the heart with KCl before a head-to-back stun lowered arterial blood pressure to 20-30 mm Hg and markedly reduced speckle. Abolition of nervously mediated muscle movement with curare before stunning resulted in no observable speckle in head-only stunned lambs but, in the head-to-back stunned lambs, there was a low incidence of speckle in the loin as a result of the muscle being directly stimulated to contract. The results from this study are consistent with the view that speckle is a result of vigorous movements between muscles during stunning, causing a shearing and rupture of blood vessels in the fat and connective tissues, thus allowing the muscles to squeeze out blood. The incidence of speckle does not appear to be related to blood pressure during stunning.