Liberal Arts Research Methods
Liberal Arts Research Methods LB 200
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Advances in Animal Welfare Science MW Fox and LB Mickley 198586 Editors Martinus Nijhoff Publisher With 1997 Updates Cardiac Arrest Stunning 0f Livestock And Poultry Temple Grandin University of Illinois Urbana Illinois Introduction A stunning method that will reliably render an animal insensible to pain and sensation prior to hoisting and bleeding is essential to prevent suffering Cardiac arrest stunning is more effective than conventional electric stunning In cardiac arrest stunning an electric current is passed through both the brain and the heart to produce permanent insensibility Since the animal is killed by the electricity it cannot revive during hoisting bleeding or slaughtering procedures In contrast conventional electrical stunning induces reversible insensibility for a short period of time Hoenderken 1978a Grandin 1980a Warrington 1974 Lambooy and Spanjaard 1982 Blackmore and Newhook 1981 The advantages of cardiac arrest stunning are outlined below If the interval between removal of the electric stunner and bleeding throat cutting is too long or if the throat is cut incorrectly an animal may enter the scalding tank or have a limb or skin removed while still conscious Cardiac arrest stunning practically eliminates this possibility compared to conventional electric stunning Another advantage of cardiac arrest stunning is if the animal accidentally misses the bleeding station stopping the heart will probably induce unconsciousness prior to the animal39s being transported to the scalding tank or the first leg removal or skinning station It has been shown that sheep become insensible 28 seconds after the heart stops without bleeding Gregory and Wotton 1984a Cardiac arrest stunning is recommended for sheep pigs calves and poultry by many researchers in this area including Blackmore and Newhook 1981 Gregory and Wotton 1984d Lambooy and Spanjaard 1982 Heath 1984a and the Agricultural and Food Council 1984 A third advantage of cardiac arrest is that its use will help reduce injuries to slaughter plant employees from the animals39 kicking during bleeding as the spasms associated with conventional electric stunning are greatly reduced or eliminated Gilbert 1980 Gilbert et al 1984 Insensibility Times Table 1 shows the period of insensibility which is induced by conventional electric stunning It also shows the time required for insensibility to occur due to oxygen deprivation from loss ofblood after both correct and incorrect bleeding methods For futher information on the assessment of insensibility refer to Lopes da Silva 1983 and Blackmore and Newhook 1983 If the time required to induce unconsciousness from bleeding exceeds the length of the insensibility period induced by the stunner the animal may feel pain and suffer Incorrect bleeding methods may greatly extend the time required for unconsciousness to occur from loss of blood For example loss of sensibility may be delayed by cutting the blood vessels on only one side of the neck Blackmore and Petersen 1981 reported that failure to cut the blood vessels on both sides of the neck of sheep occurred 4 to 47 percent of the time depending on the skiIls of the individual slaughter worker Bleeding by an unskilled person may delay the onset of insensibility in pigs to over 60 seconds Hoenderken 1978b In poultry failure to sever the carotids with an automatic neck cutter lengthened the time required for the bird to die Agricultural and Food Research Council 1984 Figs and sheep lose consiousness relatively quickly after bleeding compared to calves table 1 Studies by different researchers on pigs and sheep have similar results Sheep lose consciousness quickly after bleeding because the entire brain is supplied by blood from the carotid arteries Baldwin 1971 Blackmore 1985 personal communication In calves however the brain is supplied by both the carotid and the vertebral arteries Baldwin 1971 While the carotids are severed during bleeding the vertebral arteries are not After the throat is cut calves may still receive blood to the brain via the vertebral arteries Newhook and Blackmore 1982 Blackmore 1985 personal communication Newhook and Blackmore 1982 report that young calves remain sensible for 65 to 85 seconds after the throat is cut with a possible resurgence of sensibility up to 123 to 323 seconds later In older calves 31 to 42 days of age the onset of unconsciousness was 28 to 168 seconds after bleeding Blackmore et al 1983 The results of these two studies are in con ict with the findings of Nangeroni and Kennett 1963 Schultze et al 1978 and Gregory and Wotton 1984b table 1 Blackmore et al 1983 is unable to explain why their results differed from those of Schultze et al 1978 and Nangeroni and Kennett 1963 Gregory and Wotton 1984a state that calves became insensible within 17 seconds After the throat cut responsiveness of the brain was measured utilizing electrocortigrams while a light was ashed in the calfs eyes The retina of the eye fails very quickly when it is deprived of oxygen or blood US Navy 1968 Fraser 1973 Vision is lost almost instantly when acceleration in a centrifuge forces blood out of the retinal blood vessels Duane 1954 Newsom et al 1968 Severance of the carotid arteries during slaughter would cut off the major blood supply to the eye in both calves and sheep thereby causing loss of vision Blackmore 1985 personal communication Vision will fail prior to the onset of unconsciousness Fraser 1973 US Navy 1968 Vecchio 1977 Chambers 1963 but the auditory system is much more resistant to lack of oxygen Heath and Williams 1977 There is some evidence that hearing may still be functional during the early stages of unconsciousness Chambers 1963 New research indicates that visually evoked responses and somatosensory evoked responses disappear at approximately the same time after the throat is cut NG Gregory 1985 personal communication After bleeding visually evoked responses persist in poultry for at least one minute after spontaneous cortical activity has stopped Daly 1985 At the present time there is no good explanation for the apparent con ict between Gregory and Wotton 1984a and Blackmore et al 1983 and Newhook and Blackmore 1982 Further studies by Blackmore 1984 indicate a large difference in the reactions of sheep and calves after the carotid arteries and jugular veins were cut Sheep and lambs ceased coordinated attempts to rise after 8 to 11 seconds and 1 to 7 day old calves stopped attempting to rise at an average of 39 seconds If one carotid becomes occluded the time was extended to 385 seconds The time for an adult bull was 20 seconds A stunning method which produces either permanent or prolonged insensibility is essential for humane stunning of calves Lambooy and Spanjaard 1982 Newhook and Blackmore 1982 I have observed calves reviving during bleeding in slaughter plants when conventional electric stunning was used Calves may revive even if they are bled immediately after conventional electric stunning In sheep and pigs bleeding should take place within 10 to 17 seconds after conventional stunning to insure that the animals do not return to sensibility Lambooy 1982 Blackmore and Newhook 1981 Leach 1978 In pigs the absolute maximum allowable interval is 30 seconds Hoenderken 1978a Too long an interval between conventional electric stunning and bleeding is unfortunately a common occurrence in some slaughter plants Gregory and Wotton 1984c Table 1 Insensibility Times conventional Incorrect Bleedin Electric Correct Bleeding Method M g ethod Stunning s Insensibility Onset of insensibility due to hypoxia onset 0f msgnsmlllly pecles due to hypox1a anox1a perio anox1a from bleeding from bleedin 3 1842 sec Sheep Blackmore amp 27 sec Newhook amp Blackmore 1982 iiiihgjvfggg amp Newhook 1982 1115 1amp4sc Visual evoked potential Gregory 70298 sec Gregory amp 1982 otton 1984 Wotton 1984 3362 sec Nan eroni amp Kennett 1963 46 sec Schulze et al 1978 811 sec Stops attempts to stand Rlar kmnre 1984 32 minimum sec Pigs X66 Hoenderken 1220 sec Hoenderken 1978b 86039 Hoenderken 1978 348 sec 1245 Swatland et al 25 sec Blackmore amp Newhook 1981 1984 Calves amp Cattle 1week 39 sec Stops attempt to stand Blackmore 385 sec Stops attempt to Old 1984 stand Rlarkmnre 1984 6585 sec up to 123323 onset Resurgence of possible sensibility Blackmore et al 1983b 17 sec Visual evoked potential Gregory amp Wotton 1984b 45 to 8 3661 sec weeks Blackmore amp 4469 sec Nangeroni amp Kennett 1983 old Newhook 1982 28168 sec Fquot et al 1983 6 2141 sec months Lambooy amp 10 sec Levinger 1979 6amp2nsdi gagimg around to adults Spaniaard 1982 20 sec Stops attempts to stand Rlar kmnre 1984 3060 sec Eshmke Richards amp Sykes 60 sec Gregory amp Wotton 1985 3352 ESTSCngry amp 1967 Kuenzel amp Walther 1978 60 sec maximum H Note All studies electroencephalographic or electrocorticograms unless noted Cardiac Arrest Stunning To reliably induce instantaneous insensibility an electric current must pass through the brain Grandin 1980a Croft 1952 Hoenderken 1978a Roberts 1954 Enough voltage must be applied to force a sufficient current amperage through the brain Only a small portion of the total applied current actually goes through the brain Swatland et al 1984 the rest of the current remains on the surface Cardiac arrest stunning can be done three different ways headtoback headtoleg brisket or groin and sequential stun Gilbert 1980 Lambooy and Spanjaard 1982 Blackmore and Petersen 1981 The electrode which is placed on the head is similar to the electrodes used for conventional electric stunning The head electrode may be placed on the forehead on the sides or top of the head or immediately behind the ears Grandin 1980a Hoenderken 1978a Croft and Hume 1956 Gregory and Wotton 1984d The head electrode must never be placed on the neck It is possible to induce cardiac arrest with a headonly stunner but very high voltages and amperages must be used A high voltage head only stunner will not reliably stop the heart in all the animals When cardiac arrest stunning methods fail to produce cardiac arrest the animals will be rendered temporarily insensible in the same manner as conventional stunning Differences in Sensitivity and Variability There are large differences in the sensitivity to electricity of different species and in animals from different regions as well A stunner setting which will reliably induce cardiac arrest in pigs in one slaughter plant may not reliably induce it in another Practical experience and research data indicate that an animal39s sensitivity to electricity can be affected by factors such as weight fat thickness access to drinking water prior to stunning wetness of the skin mineral content or salt content in the water which is on the skin wool or hair coat length skin thickness and age Croft 1952 Hoenderken 1978a A dry pig has twice as much resistance compared to a wet pig and pigs with thick backfat had a higher resistance Solis Cortes 1984 personal communication Old laying hens with scaly legs have a higher electrical resistance than young broilers SchuttAbraham et al 1983 Pigs which have had continuous access to water are easier to stun Croft 1952 Calves have a lower resistance than pigs Lambooy and Spanjaard 1982 Another factor which may in uence the amount of voltage to induce cardiac arrest is animal contact with electrical grounds Grandin 1980a A portion of the electric current may pass through the restrainer or oor instead of between the electrodes The restrainer should be insulated to isolate the animal from electrical grounds Grandin 1980a This is especially important for pigs and calves because they are not covered with insulating wool The animal should not contact bolts or metal structures which are grounded during stunning The restrainer should also be examined to make sure that dripping water is not creating electrical grounds Cardiac arrest stunning can be applied either manually or by an automatic stunner Three advantages of an automatic system are safety for employees consistency because it will not become tired careless or sadistic and labor reduction Automatic stunners should be rugged simple and reliable Proper maintenance and adjustment is essential to insure that instantaneous unconsciousness is reliably produced Electrical Characteristics The use of a power supply that maintains a constant current amperage is recommended Constant current power sources are used in New Zealand which is a leader in cardiac arrest stunning technology Blackmore and Petersen 1981 A constant current power source maintains the amperage setting and voltage uctuates depending on the resistance of the animal It is the current which induces unconsciousness Hoenderken 1978a and stops the heart The voltage is the pressure which pushes the current through the animal Less sophisticated stunners have a constant voltage power source and the current level uctuates with animal resistance Thus the use of a constant voltage power supply is likely to produce erratic results The frequency and waveform of the stunning current can affect its ability to induce unconsciousness Most stunners in the United States and Europe operate on 50 to 60 HZ alternating current AC This is the standard frequency supplied by the power company High frequencies are less likely to induce unconsciousness compared with 50 to 60 HZ Croft reported that frequencies between 50 to 200 HZ are suitable for stunning frequencies under 25 HZ or over 500 HZ do not induce unconsciousness Croft 1952 Hoenderken 1978a reports that unconsciousness can be more effectively induced at 50 HZ compared to 1800 HZ High frequencies it was noted by Van der Wal 1978 seemed to cause pain but these frequencies provide meat quality advantages Marple 1977 Warrington 1974 High frequencies are less capable of inducing unconsciousness because they stay on the surface of the animal Horst 1984 personal communication and stunners with such frequencies that cause pain or fail to produce instant unconsciousness would not be acceptable from an animal welfare viewpoint Changing the waveform may produce meat quality improvements without compromising animal welfare The use of 150 HZ square waves on humans reliably induced a seizure and unconsciousness with a 50 percent reduction in energy Weaver et al 1977 1997 Update More information on the effects of electrical frequency during electric stunning Cardiac Arrest Stunning State of the Art Sheep Cardiac arrest stunning has been used successfully in New Zealand for many years For all cardiac arrest stunning methods the sheep are held in a conveyor restrainer or a restraining chute As sheep have insulating wool the electrodes must be designed so as to insure good contact Manual headtoback cardiac arrest stunners in New Zealand have a 3 1 8 in X 3 1 8 in 8 cm X 8 cm saddleshaped electrode which is placed on the back over the heart and two pegs which are placed on the head Water jets in the pegs and in the saddle electrode provide good electrical contact through the wool Frazerhurst 1975 This method is superior to sharp pin electrodes The electrodes are spaced 16 in 40 cm apart Gilbert and Devine 1982 Some slaughter plants space electrodes 10 in 26 cm to 13 12 in 345 cm The two pegs on the head are spaced 1 14 in 3 cm apart The electric current passes from the head electrodes to the back electrodes Gilbert and Devine 1982 In headtoleg stunning the electric current passes from the head electrodes to a leg electrode which is mounted on the bottom of the convegor restrainer To make contact through the wool water jets wet the legs Best results are obtained when the leg electrode makes good contact with the front feet Automatic headtoleg stunners have been developed in New Zealand Blackmore and Petersen 1981 report that 3 seconds39 stunning at 08 amps at 400 volts and 50 HZ induced cardiac arrest 893 percent of the time using headtorear legs contacts and 968 percent using headtoforelegs Due to the wool covering sheep are the most difficult animal on which to achieve a good electrical contact Typical New Zealand sheep stunning equipment has a maximum output of 400 volts and is adjustable from 05 to 2 am s Blackmore and Petersen 1981 Settings used to induce cardiac arrest and unconsciousness in sheep varied from 07 to 2 amps for 3 to 4 seconds Gilbert 1980 The voltage varies from 100 to 400 volts depending on the sheep39s resistance Settings of 1 amp at 300 to 400 volts 50 HZ for 3 seconds produced unconsciousness and cardiac arrest in 100 percent of adult sheep and lambs Gregory and Wotton 1984d A headtoback stunner with a 15 in 38 cm electrode spacing was used Unconsciousness was determined by an epileptiform response on an EEG Another cardiac arrest stunning method is split current or sequential stunning A high current and voltage is used for the initial head stun to induce insensibility followed by a lower current used to induce cardiac arrest Gregory and Wotton 1984d Gilbert et al 1984 Gregory et al 1984 used tongs to head stun sheep for 3 seconds at 300 volts 50 HZ 50 volts were then applied across the chest Gilbert et al 1984 applied 075 to 1 amp 50 HZ to the head for 4 seconds with two electrodes spaced 8 cm apart The heart was stopped two seconds later with a second 03 amp current which passed from one foreleg to the other for 4 seconds To prevent kicking a third 09 amp current was passed from the head to the groin after a delay of 1 to 20 seconds It was found that 100 volts was the minimum to stop the heart after the head stun During these experiments the researchers restrained the sheep by placing them astride a 10 cm 4 in wide padded bar This type of restrainer is similar to the one described by Giger et al 1977 Gilbert et al 1984 also experimented with different frequencies to stop the heart Square waves at 143 to 40 HZ and 1000 HZ at 400 volts failed to stop the heart as did square waves alternating current at 143 HZ at 400 volts Alternating current of 50 HZ was found to be the most effective 1997 Update To prevent pelt damage when a headtoback stunner is used the back electrode must be placed rmly against the back before the head electrode is applied The waterjet should be set so that a good electrical contact is made through the wool Pigs There has been relatively little formal research on cardiac arrest stunning of pigs Hoenderken 1978a 1983 found that 125 amps 50 HZ at 300 volts for 1 second was the minimum required for reliable induction of instantaneous unconsciousness in pigs Practical experience in the United States and Canada indicates that cardiac arrest can be induced with a headtoback stunner with a wide blunt at electrode or two nonpenetrating peg electrodes on the forehead or immediately behind the ears and a wide saddleshaped electrode placed on the back The wide surface area reduces electrical resistance The electrodes are spaced 12 30 cm to 18 in 36 to 41 cm apart Fourteen to 16 inches 355 to 46 cm is the most common spacing Pigs must be wetted before the stunner is applied Hoenderken 1978a Water sprays should be located in the chute where the pigs wait in line to enter the stunning restrainer Care must be taken that the animals are not dripping wet as excessive water dripping off the pigs may create undesirable electrical grounds Preliminary tests with headtoforeleg stunning indicated that 300 volts at 15 amps for 1 to 2 seconds induced cardiac arrest in pigs Swilley 1985 personal communication Some slaughter plants that did not have constant amperage power units had dif culty inducing cardiac arrest with a headtoback stunner even when the voltage was considerably higher than 300 volts Due to the insulating layer of backfat on pigs headtoleg may be the preferred cardiac arrest method for pigs Many small plants stun pigs on the oor without a restrainer In England some plants used standard stunning tongs to stop the heart in pigs The 90 volt 50 HZ tongs are rst applied to the head in the conventional manner for 15 seconds After head stunning the tongs are clamped on the pigs body for 5 seconds Warriss and Wotton 1981 It is essential that the tongs are placed on the head rst This method must be monitored carefully by slaughter plant management to avoid abuses This twophase stunning is a practical solution to the problem of long stunningtobleeding intervals in small plants that have slow hoists Many small locker type plants exceed the 30 second maximum allowable stunningtobleeding interval An automatic headtoforeleg stunner has been developed in the United States by Wilson Swilley Omeco Boss and the author The pig rides in a conveyor restrainer which was invented by Regensburger 1940 and is described by Grandin 1980c Contact is made by the pigs head with a metal ap which is hinged at the top The forelegs are contacted with two springloaded bars The current is activated when the forward motion of the conveyor causes the pigs head to push the ap up to a 45 degree angle The current passes from the ap contacting the head to the leg electrode After stunning the pig pushes the ap up to a horizontal position and is ejected from the conveyor Here again it is essential that pigs be wetted before they are admitted to the stunner In smaller plants pigs can be admitted individually into the restrainer with a gate to maintain a separation between animals In larger plants a second restrainer must be used to automatically maintain separation between the animals An automatic stunning system developed in Holland by Nijhuis Stork will induce cardiac arrest in approximately 70 percent of the animals at a setting of 700 volts for two seconds Spanjaard 1981 To induce cardiac arrest the voltages and amperages required are higher than those required for headtoback or headtoleg stunning While this system by Nijhuis is not a true cardiac arrest stunner because the electrodes are applied to the head it is an excellent conventional stunner and is used in many plants 1997 Update The most modern electric stunners for pigs use a constant amperage and the voltage uctuates with pig resistance These systems will reduce bloodsplash an hemmorhages in the meat They are also equipped with computer software that monitors the performance of the operator It counts partial stuns and double stunning Double stunning is a bad practice because it increases bloodsplash in the meat Double stunning occurs when the electrode slides during the stun This causes the current to be interrupted and then restarted which results in the animal39s muscles contracting a second time Preventing double stuns will improve meat quality by reducing bloodsplash and bloodspots in the meat The electrode must be held rmly against the animal to prevent double stuns Double stunning can also occur when electrical cords or switches are damaged Calves A stunning method that produces prolonged or permanent insensibility is absolutely essential for humane stunning of calves Blackmore and Petersen 1981 report that a headtoleg stunner set at 2 amps for 5 seconds produced 100 percent cardiac arrest These researchers also report that 1 amp applied for 5 seconds with a headtoback stunner induced cardiac arrest in 248 out of 250 baby calves while a headtoback stunner set at 08 amps produced cardiac arrest in only half the calves Present research findings indicate that 125 amps for 5 seconds would be the minimum setting for young calves A constant current power unit is recommended Headtoback and headtoleg stunning equipment for calves is similar to the equipment for sheep If the calves are wetted prior to stunning water jets in the electrodes would not be needed Sharp penetrating electrodes should not be used Lambooy and Spanjaard 1982 tested cardiac arrest stunning on large 441 lb 200 kg six monthold veal calves The stunner had two at metal prongs applied to the head and a saddleshaped electrode over the back Setting the stunner at 600 volts and applying it for 1 to 2 seconds killed wet calves immediately Cardiac arrest stunning can probably be used on adult cattle Large versions of the small animal systems would probably work however large cattle systems must be carefully researched before they are approved for general use Poultry To accomplish cardiac arrest stunning in poultry the current must pass from the water bath in which the head is submerged and through the metal shackle from which the bird is suspended by its legs The electrical resistance of poultry increases greatly as the animals age For example twoyearold laying hens required double the voltage for conventional stunning compared to siX to eightweek old broilers SchuttAbraham et al 1983 Older hens have higher resistance due to horny scales on their legs The electrical resistance of the bird39s legs can be reduced by wetting the legs with a water spray Kuenzel nd or by placing the bird39s shank in the shackle Shank shackled hens had 30 to 40 percent lower impedance compared to leg shackled hens SchuttAbraham et al 1983 The installation of needles or barbs in the shackles to decrease resistance is not acceptable for animal welfare reasons because the birds hang in the shackles from the truck unloading area to the stunner which may involve considerable time or distance Another variable which affects electrical resistance is the depth to which the birds are immersed in the water bath Plunging the birds into the water up to their wings improved stunning SchuttAbraham et al 1983 A minimum of 120 milliamps mA is required to reliably induce cardiac arrest in broilers Muller 1978 SchuttAbraham et al 1983 Heath 1984a explains that the amperage is divided between the number of birds in the water bath therefore if seven birds are in the water 840 mA is the minimum amount of current required to kill them Cardiac arrest can usually be accomplished by setting the stunner at 200 volts Heath et al 1983 Schutt Abraham et al 1983 Heath however warns that the reading on the voltage dial may over estimate the actual voltage and amperage of the stunner A setting of 100 to 120 volts killed only 51 to 75 percent of the broilers SchuttAbraham et al 1983 A setting of 75 volts killed 8 percent of the birds and a setting of 95 volts killed 35 percent Grif ths and Purcell 1984 The use of a constant current power source would probably improve poultry stunning because amperage would not uctuate when the number of birds in the water bath changed Effects on Processing Stillness When conventional headonly stunning is used the animal will kick violently due to the grand mal seizure which is induced by the stunner A grand mal seizure must occur to make the animal or bird unconscious Hoenderken 1978a Warrington 1974 Croft 1952 Croft and Hume 1956 The spasms and contractions associated with the seizure interfere with shackling and bleeding Animals are more likely to be bled incorrectly if they are rigid or kicking When conventional headonly stunning is used employees in slaughter plants will sometimes turn the stunner voltage down to reduce kicking This practice may prevent the grand mal seizure and the animal may therefore be sensible during shackling and bleeding Cardiac arrest stunning greatly reduces or eliminates kicking because the electricity passing through the spinal cord depolarizes spinal neurons Gilbert et al 1984 Practical experience with pigs and sheep indicates that a stunning time of 4 seconds will produce better stillness than will a 2 second stunning time Good electrode contact is required for effective stillness The electrode should be placed as close to the spine as possible Headtoback stunning produced better stillness in sheep than did headtoforeleg stunning Gilbert 1980 Gilbert et al 1984 The stillness produced by headtoforeleg stunning is still good However Gilbert and Devine 1982 report that higher currents are required to induce stillness in sheep with headtoforeleg stunning compared to headtoback stunning Properly applied headtoback or headtoforeleg cardiac arrest stunning will produce a relaxed carcass which is easy to bleed and process In pigs headtoforeleg stunning produced good muscle relaxation and stillness in the forequarters Observations in the United States slaughter plants indicated that replacing a small back electrode with a large saddleshaped electrode improved stillness and the carcass was more relaxed and easier to bleed Cardiac arrest induced by a high voltage headonly stunner often produced a stiff carcass which was more dif cult to bleed correctly One advantage of cardiac arrest stunning is that the more relaxed carcass allows for more accurate insertion of the bleeding knife This higher accuracy will help reduce the incidence of shoulder sticks which damage the meat A still relaxed carcass is required in countries where edible blood is collected through a hose Ritual Slaughter Recently Moslem religious authorities have prohibited the use of cardiac arrest stunning on animals which are slaughtered in New Zealand for shipment to the Middle East Headonly electric stunning is still permitted To maintain adequate stillness a current that does not stop the heart is passed through the animal after conventional head stun The current is passed from the forelegs to the hindlegs Stillness can be maintained by either a brief current spinal 139 39 or a quot current 39 39 quot39 quot A 200 Hz 80 volt current applied for 5 seconds is most effective in spinal discharge method for sheep Gilbert et al 1984 Immobilization is accomplished by 40 volt square waves at 1428 Hz A similar system has been developed for Halal slaughter according to Moslem law treatment of cattle A four second 15 to 25 amp head stun is applied in an automatic stunning pen and kicking is suppressed by immobilizing the animal with a continuous 80volt peak 15 Hz 5 msec duration square wave current Devine et al 1985 The Halal cut is made within 10 seconds after the head stun before the immobilizing current is applied Devine et al 1985 has tested this method in the laboratory with the EEG and determined that the cattle remained unconscious when the immobilizing current is applied The immobilizing current appears to prolong the period of unconsciousness which is induced by the head stun When this method was used under commercial conditions in a slaughter plant there were many serious problems Blackmore 1985 personal communication Blackmore states that the method can be further developed to be humane under commercial conditions 1997 Update Electrical stunning systems for cattle have been perfected and they work really well In the New Zealand system each bovine enters a singleanimal stunning box The operator presses a button to open and close the entrance gate After the animal enters the operator then presses a button to activate a stanchion which clamps the animal around the neck This stanchion is similar to the headgate in a squeeze chute at a feedlot Immediately after the animal39s head is clamped the operator presses another button to begin the automatic stun cycle The system applies twototwoandahalf amps at 400 volts for four seconds The current passes from the neck stanchion to a nose electrode A chinlift automatically rises to press the bridge of the animal39s nose against the nose electrode Water sprays help create good electrical contact After unconsciousness is induced a second current is applied from the neck stanchion to the brisket to induce cardiac arrest This current is threetofour amps at 450 volts applied for fourto15 seconds Besides its effect on the bovine39s heart the current also depolarizes the spine to prevent kicking Cardiac arrest by itself can be induced in two or three seconds but a little more time is needed to induce stillness in the animals Due to the large size of cattle a two stage stunning procedure must be used to insure instantaneous unconsciousness the current must be applied across the head rst After the animal is rendered unconscious a second current is applied from the head to the brisket to induce cardiac arrest A single 400 volt 15 amp current passed from the neck to the brisket failed to induce an epileptic form change in the electroencephalographic recordings To prevent bloodsplash in the meat the electrodes must be pressed rmly against the animal Making or breaking the circuit during the stun will cause bloodsplash The stunning current must be supplied by constant amperage to prevent surges that will damage the meat While the amperage remains constant the voltage will uctuate depending on the electrical resistance inherent in each animal39s body After the animal is stunned it is rolled out of the box and the system resets itself for the next animal The operator opens the tailgate admits the next animal catches the head and once again initiates the stun cycle The cycle by the way is controlled by a programmable logic controller Proper catching and handling is essential for smooth operation If there is a trick to the operation it is that the operator must begin the stun cycle immediately after catching the animal39s head If stunning is delayed the animal will ght the head stanchion I observed electric stunning of cattle in two plants and in both of them the handling was excellent The animals entered the box quietly and were stunned within one second after being caught in the stanchion That s good careful humane stunning Stunned cattle are ejected onto a moving stainless steel oor conveyor Weasand rodding is performed on the prone animal to prevent contamination from rumen contents Once this process is completed the animal is shackled and hoisted from the oor in a manner similar to the way hogs are shackled and raised For conventional slaughter the animal is then stuck while hanging39 for Halal requirements the animal is bled while still prone on the oor conveyor Halal slaughter also requires that the cardiacarrest current be shut off the animal receives only a stun to the head Thus to prevent the animal39s return to consciousness the stick in the Halal procedure must be performed within 10 seconds after stunning Neville Gregory a stun researcher from England recommends that a thoracic chest stick be performed immediately after the Halal stick to ensure absolutely that there be no return to consciousness Electrical stunning could be easily installed as part of a centertrack restrainer system A stanchion could be mounted on the end of the restrainer The current for the headstun would be applied between the neck stanchion and a nose electrode just like the systems now used in New Zealand Current to induce cardiac arrest would be applied between the neck stanchion and the conveyor under the animal39s brisket and belly Passing the current from the neck stanchion to the conveyor would probably work well on muddy cattle because the conveyor presses deep under the animal39s armpits The shackling system would have to be converted to the New Zealand system but shackling would be made much easier because of the reduced kicking For conventional slaughter cardiac arrest is the most reliable electrical method to induce and maintain insensibility Cardiac arrest stunners are simple and would probably be less likely to malfunction If an animal regained consciousness while the immobilizing current was on it would feel the shock and be paralyzed However electroimmobilization should not be used as a standard restraining method as it is aversive to conscious sheep Grandin et al 1985 Sheep will avoid entering a place where they have experienced electroimmobilization Electro immobilization was found to be more aversive than a mechanical restraining chute that squeezes and tilts the sheep to a horizontal position Carcass Bruises Sheep and cattle and to a lesser extent pigs can still be bruised after stunning Cattle stunned with a captive bolt can be bruised when they are rolled out of the stunning pen Meischke and Horder 1976 In sheep the use of cardiac arrest stunning reduced the susceptibility to bruising by 69 percent Gregory and Wilkins 1984 The use of cardiac arrest stunning would help reduce the bruises caused by the animal39s jerking shackles falling on the oor or striking sharp corners during the spasms which occur in the interval between conventional stunning and bleeding Bleeding Livestock and poultry only lose 35 to 60 percent of the total circulating blood regardless of stunning or slaughter method Warris 1984 Kotula and Helbacka 1966 Research indicates that livestock and poultry will bleed adequately after cardiac arrest stunning Stopping the heart has no effect on shelf life of the meat blood content in the muscle blood pigment levels in the muscle and bacteriological levels Chrystall et al 198081 Griffiths 1983 Warris 1984 Lambooy 1981 Weise et al 1982 In poultry there was little correlation between the amount of blood lost during bleeding and appearance of the carcass Newell and Shaffner 1950 There sometimes arises in poultry the problem ofblood trapped in the larger vessels which presents an unattractive appearance Davis and Coe 1954 Newell and Shaffner 1950 Cardiac arrest stunning applied sequentially to the head and chest of pigs with stunning tongs had no effect on the weight of the blood lost rate ofblood loss or blood retained in the carcass Warris and Wotton 1981 In one large pork slaughter plant headtoback cardiac arrest stunning caused small amounts of blood to be retained and subsequently released into the scalding tank There was no effect on meat quality There was no additional blood contamination of the scalding tank caused by headtoback cardiac arrest stunning in another plant This plant had a welltrained person doing the bleeding and a ve minute bleeding time There were no differences in the appearance or quality of the meat compared with pigs stunned with a conventional electric stunner In sheep the rate ofbleeding was slower and more blood was retained in the carcass Kirton et al 198081 Crystall et al 198081 The retained blood was located in the thoracic cavity abdominal viscera heart and lungs Warris 1984 This blood drains from the carcass during dressing procedures There were no differences in meat quality between cardiac arrest and conventionally stunned sheep Crystall et al 198081 Cardiac arrest slowed bleeding of calves Lambooy 1981 Cardiac arrest stunning greatly slows the bleeding rate of poultry but there were no signi cant differences in the total blood loss after 180 seconds Weise et al 1982 Schutt Abraham et al 1983 Blood loss at 90 seconds after bleeding was signi cantly less Birds which had not been bled at all could not be distinguished from normally bled birds on the dressing line Heath et al 1981 Weise et al 1982 found that a taste panel could detect no difference in the meat of cardiac arrest and conventionally stunned birds and there was no adverse effect on muscle pH juice retention or keeping quality Some people believe that a condition called quotredskinsquot a cherry red color widespread on the carcass is caused by killing birds with the electric stunner Heath et al 1983 found that redskins are probably birds which entered the scalding tank alive Red skin carcasses are produced when live birds enter the scald tank Grif ths and Purcell 1984 Cardiac arrest stunning would prevent this problem Veerkamp and de Vries 1983 report that poultry stunned at 200 volts in a brine stunner had signi cantly more reddened wing tips and tails than birds stunned at 75 volts These authors did not indicate whether or not the higher setting induced cardiac arrest Red wing tips are caused by rupture of small blood vessels when the feathers are removed Heath 1984b Reddened wing tips and redskins may be caused by different physiological mechanisms Accelerating Bleedout One possible disadvantage of cardiac arrest stunning is increased BOD biological oxygen demand from blood in the scalding tank and losses in total blood collection Blood has a high organic content Harris and Carter 1977 and its presence in the plant39s waste water would increase sewage treatment costs Many poultry plants have a 60 second or less bleeding time Harris and Carter 1977 and doubling the bleeding time would force some plants to make expensive alterations or entail the building of additions to lengthen the bleeding rail In general pork slaughter plants will have minimal problems and poultry plants will have the greatest problems in converting to cardiac arrest stunning Cardiac arrest stunning is used commercially in New Zealand on sheep the advantages of increased carcass stillness far outweigh the disadvantage of slightly slower bleedout A simple electrical carcass stimulator greatly reduced scald tank contamination in one pork plant This device shocks the carcass during bleedout at 16 to 32 volts at 60 HZ Dried blood yields in a plant with a stimulator and cardiac arrest stunning were at normal industry levels 1997 Update Electrical stimulation of the carcass will cause PSE and lower pork quality It will also reduce the yield of processed product made from the pork An electrical stimulator used to tenderize and condition beef carcasses increased blood losses from the carcass National Provisioner 1979 The use of rhythmic electrical stimulation to speed up bleeding in poultry has been suggested by Muller 1978 Stunning poultry at 480 HZ was found to improve bleedout Kuenzel et al 1978 The use of high frequencies may make a bleedout stimulator more effective There is some concern that stimulating the carcass may lower meat quality in pigs by lowering muscle pH Jensen et al 1978 This would not be a problem in veal beef or lamb as in these species electrical stimulation is used to improve meat quality Cross 1979 There have been many studies to determine the best voltage waveform and pulse time for electrical stimulation for tenderizing and conditioning meat Cross 1979 Reports from the Commonwealth Scientific Industries Research Organization CSIRO in Australia contain information on waveform and frequency CSIRO 1983 1981 This information could be used as a starting point to develop inexpensive and practical bleeding rate accelerators If excessive pH drop is a problem in pigs the use of vibration may help remove the blood faster Bloodsplash Speckle and Hemorrhages Electric stunning sometimes produces hemorrhages in the muscle fat and connective tissue These hemorrhages cause economic losses as they damage the appearance of the meat The wholesomeness of the meat is not affected except in severe cases when bloody meat is trimmed Sometimes the damage is so severe that an entire ham or chicken may be rejected The European pork industry may suffer greater economic losses due to hemorrhages because their pork is sold with the skin intact In the United States however super cial speckling in the fat can be trimmed away Countries and meat plants which export have greater losses due to hemorrhages because the importing country will sometimes reject or downgrade blemished meat Failure to distinguish between hemorrhage types may account for some con icting reports in the literature Bloodsplashes are hemorrhages which occur in the muscle and internal organs Leet et al 1977 Splashes range in size from pin heads to half an inch 125 cm Speckle is small quotsalt and pepperquot hemorrhages which occur in the fat and connective tissue around muscles Thornton et al 1979 Gilbert 1980 Petersen and Wright 1982 The biological mechanisms which cause bloodsplash and speckle may be different Petersen and Pauli 1983 Animal Susceptibility to Hemorrhages There are many factors which will either increase or decrease an animal39s susceptibility to hemorrhages The stunning method is only one factor Observations in pork and beef plants in the United States and Canada indicate an increase in the number of animals with hemorrhages in the fall and early winter when temperatures uctuate Hemorrhages may increase when the temperature rises after a cold spell There is evidence that vasodilation increases the amount of speckle Devine et al 1983 As the season progresses from fall to winter the susceptibility to hemorrhages decreases in lambs Petersen and Wright 1982 Hemorrhages decrease when the temperature becomes uniformly cold Natural causes of bloodsplash have a larger effect on bloodsplash severity than do different electric stunning methods Kirton and Frazerhurst 1983 There is also a tendency for lambs slaughtered early in the day to have less speckle Bloodsplash levels changed on different slaughter days Kirton and Frazerhurst 1983 A Danish study indicated bloodsplashing levels in pigs were not affected by holding time in the stockyards sugar feeding and type of truck used to transport pigs Nielson 1977 Observations in the United States and Canada indicate that resting animals before slaughter may reduce hemorrhages as livestock are transported much greater distances in North America There are also differences in hemorrhage susceptibility among groups of animals For example sheep from some farms had more bloodsplash than sheep from other farms Pearson et al 1977 and lambs that ate coumarin anticoagulant producing plants had more bloodsplash Restall 198081 There also may be genetic factors to consider as pigs from different regions or countries may be hemorrhage resistant or hemorrhage prone Large heavilymuscled pigs have a tendency to have more hemorrhages and fractures Younger animals may also be more susceptible Thornton et al 1979 Stunning Method Effects While captive bolt and CO2 stunning usually produce less hemorrhages compared to electric stunning Larsen 1983 Blackmore 1983 problems with these systems do exist For example concerns about the humaneness of the use of CO2 for slaughter have been expressed Hoenderken 1978 Grandin 1980a Regarding the captive bolt this method has a detrimental effect on meat quality in pigs and therefore electric stunning is the preferred method Grandin 1980d Overstreet et al 1975 In sheep and calves electric stunning is more economical and the brains a consumer product are not contaminated by a penetrating captive bolt The nonpenetrating captive bolt which does not contaminate the brains induces insensibility in only 80 to 95 percent of lambs according to Blackmore 1983 and unless this system is improved it is not to be considered acceptable for lambs or sheep Cardiac arrest stunning produces less bloodsplash in the muscle compared to conventional electric stunning Kirton et al 198081 Gilbert and Devine 1982 Gilbert 1980 Bloodsplash is reduced because heart stoppage prevents a blood pressure rise after the stunning Kirton et al 198081 It appears however that blood pressure changes during stunning do not in uence the amount of speckle Gilbert and Devine 1982 Gilbert and Devine 1982 report that headtoback stunning has minimal bloodsplash but will produce speckling in lambs Headtoforeleg cardiac arrest stunning was found to be the best method as it produced less speckle and bloodsplash than either headonly or headtoback cardiac arrest in sheep Gilbert 1980 Gilbert and Devine 1982 Headtoback leg application of the stunner will produce more speckling than will headtoforeleg application when the lambs are held in a V conveyor restrainer Blackmore and Petersen 1981 Shortening the distance between the electrodes on a headtoback stunner reduced speckle in lambs a span of ten inches 26 cm was found to produce better results than 135 inches 34 cm Petersen and Wright 1982 The springloaded foreleg electrode must remain in firm contact with the legs as making and breaking the contact may increase bloodsplash and speckle Effect of Restrainer The type of restrainer used to hold the animal during stunning can affect the amount of bloodsplash and speckle AVconveyor restrainer with a steep angle of 15 degrees from vertical on each side caused greater amounts of speckle than did a restrainer with the conveyors on a 55 degree angle Thornton et al 1979 An electrode position and stunner setting which causes speckle in a Vconveyor restrainer may not cause speckle in some other type of restrainer such as the double rail or stunning without a restrainer When sheep were restrained in a hammock headtoback cardiac arrest stunning produced no bloodsplash or speckle and conventional headonly stunning produced lesions in 10 percent of the animals Gregory and Wotton 1984d Observations by Mattson 1984 personal communication of the Swedish Meat Research Institute indicated that pigs stunned on the oor had fewer hemorrhages However accurate placement of the stunner is more difficult when the animals are on the oor and pigs stunned in such a manner are also more likely to have broken shoulders Van der Wal 1976 Human activities may also affect carcass quality For example observations in a pork slaughter plant indicated that more bone compression fractures occurred after lunch and coffee breaks This was probably due to the animals being left in the restrainer Observations with electrically stunned calves indicated that shortening the period of time the animal remains in the restrainer may reduce hemorrhages It is the author39s opinion that the effect of the restrainer on hemorrhages is not caused by adrenalin secretion or psychological stress as I have observed pigs sleeping in the restrainer during lunch Injections of adrenalin do not cause speckle Gilbert 1980 The increase in homorrhages is due to the skin being stretched just before or during stunning when the animal moves against the side of the restrainer Gilbert and Devine 1982 In a pork plant bloodsplash and speckle increased when one side of the restrainer conveyor was broken and the animals39 rubbing against the immobile conveyor stretched the skin and muscles Excitement is likely to cause speckle because an excited animal will struggle and ght the restrainer Mechanical stretching of the skin and muscle and opposing muscle groups interacting with each other during tonic contracture at stunning is believed to be a cause of speckle Gilbert and Devine 1982 Stunning Time Voltage Amperage and Frequency Effects Shortening the interval between electric stunning and bleeding will help prevent hemorrhages in pigs and sheep Warrington 1974 Burson et al 1983 Calkins et al 1980 Van der Wal 1978 L Davey Meat Research Institute of New Zealand stated that bleeding sheep within 8 seconds after removal of the stunner greatly reduced hemorrhages Practical experience indicates that when a voltage regulated stunner is used the number of compression fractures and severe hemorrhaging in the hams of pigs is increased when the voltage was raised In lambs long stunning times and higher currents produced more speckle in the leg muscles with a headtoback cardiac arrest stunner than did short stunning times and lower currents Devine et al 1983 In pigs longer stunning times of 12 seconds with 320 volt 50 HZ head only stunning produced more hemorrhages and broken bones than did a 2 second time Braathen and Johansen 1984 The use of constant current stunners would help prevent hemorrhages because high current surges would be eliminated A Danish study on pigs indicated that 700 volt headonly stunning in an automatic system greatly reduced shoulder hemorrhages compared to a 300 volt manual headonly stunning Larsen 1983 The 700 volt system induced cardiac arrest in many of the pigs Stunning times were not given but the 700 volt automatic system usually has a shorter stunning time than does a 300 volt manual The incidence of fractures in both systems was approximately 1 percent Increasing the voltage in a poultry stunner greatly increases the number of birds damaged by hemorrhages in the wingjoints and broken bones according to R Lewis Wesley Virginia State University personal communication 1984 Stephen Pretanik Director of Science and Technology National Broiler Council personal communication 1985 also states that quotWhen electric stunners are set at a level sufficient to kill the bird considerable internal damage is caused to the birdquot Some examples of the damage are broken bones and bloody areas in the meat and joints Turkeys have severe contusions of the breast muscles and bloodsplash if the amperage is too high Howard Hunter 1984 personal communication Wesley personal communication 1984 states that damage can be prevented by conventional stunning at less than 40 volts at high frequency for 7 seconds Kuenzel and Walther 1978 recommend 480 HZ There is a need for research to verify that this method of conventional stunning induces unconsciousness According to Kuenzel and Walther 1978 a peak voltage of 100 volts average voltage of 30 volts at 480 HZ is required Electric Prods The use of electric prods to drive animals may increase bloodsplash and speckle Calkins et al 1980 found that pigs driven with an electric prod had almost twice as many hemorrhages compared with pigs driven with a leather strap The exact specifications of the prods was not known but they were either connected to a transformer which stepped down the voltage from 120 volts AC 60 HZ or they had a small light bulb wired in series to serve as a resistor Although it is illegal to connect prods directly to the house current without a transformer some plants still engage in this practice Observations in Europe indicated that it was difficult to induce hemorrhages by prodding pigs in the leadup chute with a battery operated electric prod Lambooy 1984 personal communication A prod wired to a transformer has only a single contact and the electricity ows through the animal to the ground This causes muscles to tense up A battery prod has two contacts and the electric shock is localized Pork plants with electric prods wired through a transformer found they could reduce hemorrhages and broken aitch hip bones by lowering prod voltage to 1416 volts 1997 Update Modern lean pigs are more susceptible to bloodsplash and hemorrhages compared to older fatter type pigs Experience in large plants indicates that reducing or eliminating the use of all types of electric prods will improve pork quality Excitement caused by electric prods will cause pigs to overheat and increase PSE Excited pigs are more likely to pile up and jam in races Pigs jammed against each other or jammed against equipment can have broken capillaries tiny blood vessels This may result in pinpoint blood spots after the pigs are stunned Shackle Jerking and Leg Movement Jerking the leg of a stunned animal by the shackle chain can cause blood vessels to break in the ham Sometimes hemorrhage problems caused by the jerking of shackle chains are blamed on the stunning method Systems for conveying the stunned pig should be designed to lift it up smoothly without jerking the shackled leg The animals legs must be able to move freely during the spasm which occurs during stunning otherwise broken aitch bones and hemorrhages will result if the animal39s feet hit an obstruction under the restrainer Beveling the edges of the restrainer slats at the point where the legs contact may enable the legs to slide more freely during the spasm PSE and Electric Stunning Stunning and slaughter methods can affect the incidence of PSE pale soft exudative meat in pigs Grandin 1980d Athen et al 1977 Larsen 1983 This condition lowers meat quality in pork Grandin 1980d Van der Wal 1978 but rarely causes meat quality problems in lambs calves or cattle Shortening the stunner application time from 12 seconds to 2 seconds reduced PSE Braathen and Johansen 1984 Marple 1977 Van der Wal 1978 because shorter application times have less of an effect on muscle pH Devine et al 1984 In sheep head only stunning produced a smaller drop in muscle pH than headtobackcardiac arrest stunning Devine et al 1984 Petersen and Blackmore 1982 In pigs a lower muscle pH is usually related to increased PSE A Danish study in pigs indicated that 700 volt headonly automatic stunning caused slightly less PSE than 300 volt headonly manual stunning Larsen 1983 The 700 volt stunner induced cardiac arrest in many pigs A Dutch study by Van der Wal et al 1983 with similar equipment showed a tendency for the 700 volt stunned pigs to have a lower pH and higher carcass temperature The con icting results are probably due to differences in the methods for measuring PSE or confounding of the Dutch trial by carcass grade PSE measurements with an optical probe and pH sometimes give different results Larsen 1983 Swatland personal communication 1984 and Van der Wal 1978 state that kicking and muscular contractions after stunning increases PSE Pigs kick violently after conventional stunning The use of cardiac arrest stunning with a short application time may help reduce PSE because damaging heat buildup in the muscles caused by kicking would not occur Pigs kick more violently after conventional stunning than do sheep and heat buildup may occur more quickly due to the heavy layer of insulating fat Practical experience in large North American slaughter plants indicates that shortening the interval between stunning and bleeding helped reduce PSE Other PSE Factors There are many causes of PSE which have a greater in uence on its incidence than do differences in electrical stunning methods PSE is a complex condition which is caused by the interaction of many different factors Grandin 1984 Canadian Meat Council 1980 Eikelenboom 1984 One of the most important factors is genetic stress susceptibility or PSS porcine stress syndrome as evidenced by the fact that different pig breeds and strains within a breed or crossbreed have different levels of PSS Tarrant et al 1979 Eikelenboom 1984 Other factors may affect PSE incidence as well Fluctuating temperatures and unstable weather conditions may double the incidence of PSE Handling at the slaughter plant is very important also Well designed chutes are essential as is the proper human handling Grandin 1982 1985 If they become excited in the chute leading to the stunner normally stress resistant pigs will have more PSE and lower meat quality BartonGade 1984 Observations in packing plants indicate that gentle handling in the stunning chute reduces PSE Showering pigs in the stockyards helped reduce PSE mainly by lowering body temperature Smulders et al 1983 In another study showering had no effect on PSE incidence during cold weather Mattson 1984 personal communication These ndings illustrate the importance of keeping pigs cool and avoiding overheating A short fourhour rest period after arrival at the slaughter plant is beneficial for meat quality Malmfors 1982 Observations in North American slaughter plants indicate that slaughtering pigs immediately after arrival at the plant is detrimental to meat quality Abasic principle is that a longterm stress tends to make meat darker and drier than normal and a shortterm stress tends to increase PSE Nielson 1977 Grandin 1980d Pigs which have been on a long truck ride often have a lower incidence of PSE Grand in 1980d Longhaul pigs have less PSE because glycogen muscle fuel is exhausted There are unknown factors which determine the incidence of PSE There are some exceptions to the shortterm and longterm stress principle Breeds or strains of pigs that are more excitable may have high levels of PSE after a long truck ride Fatigued cattle sometimes have a PSElike condition after electrical stimulation of the carcass FjelknerModig and Ruderus 1983 A similar condition may exist in electrically stunned fatigued pigs Some of the con iciting data is due to the possibility that there are different kinds of PSE with different physiological mechanisms Monin and Sellier 1985 Grandin 1984 Monin and Sellier 1985 found that normal stressresistant pigs of the Hampshire breed often have inferior meat quality This breed of pig has higher levels of glycogen Different measuring methods might provide different readings in genetically stresssusceptible and normal pigs Barton 1984 personal communication Conclusions Cardiac arrest stunning is de nitely recommended for the humane stunning of hogs sheep and calves To induce instantaneous unconsciousness the electric current must pass through the brain Humane cardiac arrest stunning can be accomplished by placing the positive electrode on the animal39s head and the ground electrode may contact the back forelegs hindlegs brisket or groin Another cardiac arrest stunning method is to pass a current through the head first A second current is then passed through the heart Sufficient amperage must be applied to cause unconsciousness Minimum amperage settings for wet animals with good electrode contact are market hogs 125 calves 125 shorn lambs 075 Higher settings may be needed to induce unconsciousness if animals are old dehydrated have long hair or wool heavy backfat or dry hair or wool There are many variables which will change amperage requirements Amperage settings higher than these minimums will be required in many slaughter plants Author39s Addendum Is EIectroimmobilization Humane A Review of Recent Studies There have been concerns about the humaneness of electroimmobilization of livestock Batteryoperated electroimmobilizers have been developed to restrain cattle for veterinary procedures such as dehorning and sheep for shearing The devices immobilize the animals by passing a small electrical current through their bodies The animal is held rigid by contractions of its muscles The manufacturers of these devices claim that immobilization relieves pain and is less stressful than are conventional mechanical restraints such as squeeze chutes Two different research laboratories have found that electroimmobiiization does not block the sensation of pain Animals will react to painful stimuli while they are immobilized Lambooy and van Voorst 1983 Lambooy 1985 Amend 1983 states that there is no reliable evidence that electroimmobilization is a pain reliever Studies with the EEG in calves and sheep indicate that electroimmobilization does not induce electroanesthesia or electro sleep Lambooy and van Vorst 1983 The animals remain sensible during electro immobilization Research conducted by Grandin Curtis Widoski and Thurmon 1985 indicates that electro immobilization is more aversive disliked than is restraint in a squeeze tilt table In a choice test sheep preferred to be restrained in the squeeze tilt table The choice tests were conducted in a specially designed sheep handling facility It had a Ychute which led to either an electro immobilizer or to a squeeze tilt table which tilted the sheep to a horizontal position Each animal was given several choice tests Ewes which made a choice were rewarded with grain after they were immobilized or restrained in the squeeze tilt table Ewes that refused to make a choice within ve minutes were released They were not given a grain reward Three different commercially available electroimmobilizers were tested The sheep39s choices in three different trials were electroimmobilizer 13 percent 13 percent and 8 percent respectively squeeze tilt table 79 percept 57 percent and 71 percent and no choice 8 percent 30 percent and 21 percent Ninetyfour percent of the sheep chose the squeeze tilt table again after experiencing it once but 56 percent of the sheep never chose the electro immobilizer again after experiencing it once The sheep became less willing to enter the handling facility after they had experienced both the electroimmobilizer and the squeeze tilt table Some sheep had to be grabbed and forced into the chute Electroimmobilization also reduced the sheeps39 acceptance of a feed reward All of the sheep which chose the squeeze tilt table accepted the grain reward but many of the sheep that were electroimmobilized either refused the reward or only took one bite The day after the choice tests were conducted many of the sheep were still reluctant to enter the handling facility Gradually the sheep were coaxed into the chute with a bucket of grain and put in the squeeze tilt table As experience with the tilt table only increased the sheep became progressively more willing to enter the table for the grain reward Some animals entered the squeeze tilt table repeatedly and were willing to be squeezed and tilted for the grain reward A study by Pascoe and McDonnel 1985 also indicated that electroimmobilization was aversive They trained Holstein cows to enter a set of stocks The cows were subjected to four different treatments in the stocks The treatments were control held in the stocks only saline injection immobilizer low setting and immobilizer high setting These treatments were repeated ten times Cattle which had been immobilized became more reluctant to enter the stocks They had higher heart rates upon entering than the controls or the cows which received the saline injection The immobilized cows also showed a more pronounced emotional reaction before they received the shock The authors concluded that electroimmobilization was painful Carter et al 1983 reports that onethird of the cattle bellowed when the immobilizer current was turned on I tried putting all three commercially available immobilizers on my own forearm The sensation felt like getting a shock and it was very disagreeable The sensation was similar at both high and low settings Different people have reported different reactions to placing the immobilizers on themselves from a thudding sensation to a very painful one It is likely that different people and animals may react differently In sheep and calves there are large individual differences in the amount of current required to maintain immobilization Lambooy and van Voorst 1983 Some animals required almost twice as much current Carter et al 1983 measured cortisol stress hormone levels in cattle after they were dehorned There were three different groups immobilized during dehorning no immobilization during dehorning and local anesthetic prior to dehorning There were no signi cant differences in the cortisol levels between the three groups The local anesthetic group may have failed to have lower cortisol levels because they had been handled four times The other two groups were handled only twice It is likely that dehorning is such a painful experience that the cortisol levels reached maximum levels in both the immobilized and non immobilized cattle More recent research by Lambooy 1985 indicated that electro immobilization is stressful The pulse rate and plasma cortisol level increased greatly during current administration in calves sheep and pigs Lambooy 1985 concludes quotBecause of the dubious effects on the animal39s welfare the use of such an apparatus Feenix Stockstill cannot be recommended quot For animal welfare reasons I do not recommend electroimmobilization for routine husbandry procedures such as shearing dehorning or castration A good sturdy squeeze chute is recommended for cattle Electroimmobilization must never be used as a substitute for anesthetics during major surgery Pascoe personal communication Refe re n ce 5 Agricultural and Food Research Council 1984 A practical guide to neck cutting in poultry MRI Memorandum No 54 Meat Research Institute Langford Bristol England Amend JF 1983 Preliminary verdict for electroimmobilization Int I Study of Anim Probs 4 1 113 Athen TG Ono K and Ibpel DG 1944 Effect of stress susceptibility or stunning method on catecholamine levels in swine Journal of Animal Science 449859 Baldwin BA 1971 Anatomical and physiological factors involved in slaughter by carotid section In Humane Killing and Slaughterhouse Techniques Universities Federation for Animal Welfare Potters Bar Hert England pp 3443 BartonGade P 1984 In uence of halothane genotype on meat quality in pigs and subjected to various preslaughter treatments 30th European Meeting of Meat Research Workers Proceedings Bristol England 13 pp 89 Blackmore DK 1983 Problems associated with percussion stunning in sheep In Stunning of Animals for Slaughter Eikelenboom G ed Boston Martinus Nijhoff pp 14653 Blackmore DK 1984 Differences in behaviour between sheep and cattle during slaughter Res Vet Sci 372236 Blackmore DK and Newhook JC 1981 Insensibility during slaughter of pigs in comparison to other domestic stock New Zealand VetJ 292192 Blackmore DK and Petersen GU 1981 Stunning and slaughter of sheep and calves in New Zealand New ampaland Vet J 2999 102 Blackmore DK and Newhook JC 1983 The assessment ofinsensibility in sheep calves and pigs during slaughter In Stunning of Animals for Slaughter Eikelenboom G ed Boston Martinus Nijhoff pp 1325 Blackmore DK Newhook JC and Grandin T 1983 Time of onset of insensibility in four to sixweek old calves during slaughter Meat Sci 9 1459 Braathen OS and Johansen J 1984 The effects of short or long electrical stunning times on pork quality 30th European Meeting of Meat Research Workers Proceedings Bristol England pp 2223 Burson DE Hunt MC Schafer DE Beckwith D and Garrison JR 1983 Effects of stunning method and time interval from stunning to exsanguination on blood splashing in pork J Anim Sci 5791821 Calkins CR Davia GW Cole A B and Hutsell DA 1980 Incidence ofblood splashed hams from hogs aubjected to certain antemortem handling methoda J Anim Sci 50 Supplement A Abstract Canadian Meat Council 1980 Guide to PSE Pork Canadian Meat Council Islington Ontario Canada Carter PD Johnston NE Corner LA and Jarrett RG 1983 Observations on the effect of electroimmobilization on the dehorning of cattle Austral Vet J 60 1719 Chambers RM 1963 Operator performance in acceleration environments In Unusual Environments and Human Behavior Burna NM Chambers RM and Hendler E eds London Free Press of Glencoe Chrystall BB Devine CE and Newton KG 198081 Residual blood in lamb musclea Meat Sci 533945 Cook CJ Devine CE Gilbert KV et al Electroencephalograms and electrocardiograms in young bulls following upper cervical vertebrae to brisket stunning N Z Vet J 199139121 125 Cook CJ Stunning ScienceA guide to better electrical stunning Meat Focus 199323128 13 l Croft PS 1952 Problems of electrical stunning Vet Rec 6425 58 Croft PG and Hume CW 1956 Electric stunning of sheep Vet Rec May 26 pp31821 Cross HR 1979 Effect of electrical stimulation on meat tissues and muscle properties A review J Food Sci 4450923 CSIRO 1981 Effective electrical stimulation of beef carcasses and sides No 815 1981 CSIRO Division of Food Research Brisbane Australia CSIRO 1983 Effective extra low voltage electrical stimulation of beefWhat you need to know Meat Research Newsletter Vol5 September 26 CSIRO Div of Fbod Research Brisbane Australia Daly CC 1985 Visually evoked responses during slaughter Vet Rec Letters to the Editor May 25 1985 pp 5745 Davis LL and Coe ME 1954 Bleeding of chickens during killing operations Poultry Sci 3 3 6 169 Devine CE Gilbert KU and Ellery S 1983 Electrical stunning of lambs The effect of stunning parameters and drugs affecting blood ow and behavior on petechial hemorrhage incidence Meat Sci 924756 Devine CE Ellery S Wade L and Chrystall BB 1984 Differential effects of electrical stunning on the early postmortem glycolysis in sheep Meat Sci 113019 Devine CE Gilbert KV Tavener A and Day A 1985 The use of electrical stunning followed by electroimmobilization for the humane slaughter of cattle New Zealand Veterinary Journal 33 47 Duane TD 1954 Observations on the fundus oculi during blackout AMA Archives of Opthalmology 5134355 Eikelenboom G 1984 An overview of PSE in Europe Proceedings 64th Annual Conference Canadian Meat Council Islington Ontario Paper 91 FjelknerModig S and Ruderua H 1983 The in uence of exhaustion and electrical stimulation on the meat quality of young bulls Part IltPost mortem pH and temperature Meat Sci 8185201 Fraser TM 1973 Sustained linear acceleration Parker JF and West VR eds Bioastronautics Data Book 2nd edition Scientific and Technical Information Of ce NASA Washington DC Frazerhurst LF 1975 Interim report on current developments in electrical stunning of sheep and lambs Meat Research Institute of New Zealand MIRINZ 442 19 Giger W Prince RP Westervelt RG and Kinsman DM 1977 Equipment for lowstress animal slaughter Transactions of ASAE 205718 Gilbert KU 1980 Developments in stunning and slaughter 21st Meat Industry Conference MIRINZ Hamilton New Zealand pp 1825 Gilbert KV and Devine CE 1982 Effect of electrical stunning method on petechial hemorrhages and on the blood pressure of lambs Meat Sci 7 197207 Gilbert KY Devine CE Hand R and Ellery S 1984 Electrical stunning and stillness of lambs Meat Sci 114558 Grandin T 1980a Mechanical electrical and anesthetic stunning methods for livestock Int I Study Anim Probs 124263 Grandin T 1980b Is your hog stunner insulated Meat Processing February 69 Grandin T 1980c Designs and specifications for livestock handling equipment in slaughter plants Int I Study Anim Probs 1178200 Grandin T 1980d The effect of stress on livestock and meat quality prior to and during slaughter Int I Study Anim Probs 131337 Grandin T 1980e Problems with kosher slaughter Int J StudyAnim Probs 1637590 Grandin T 1982 Pig behavior studies applied to slaughter plant design Applied Anim Ethol 914151 Grandin T 1984 Reducing PSE losses Meat Processing 2335356 Grandin T 1985 How to design hog chutes Meat Processing May Grandin T Curtis SE Widowski T and Thurmon JG 1985 Aversiveness of restraint by electro immobilization or in squeeze tilt table Journal of Anim Sci Suppl Abstract 6 1213 14 Gregory NG Slaughter technology electrical stunning of large cattle Meat Focus199339213236 Gregory NG and Wilkins LJ 1984 Effect of cardiac arrest on susceptibility to carcass bruising in sheep JSci Food Agric 356716 Gregory NG and Wotton SB 1984a Sheep slaughtering procedures 11 Time to loss of brain responsiveness after exsanguination or cardiac arrest British Vet J 14035460 Gregory NG and Wotton SB 1984b Time of loss ofbrain responsiveness following exsanguination in calves Res in Vet Sci 371413 Gregory NG and Wotton SB1984c Sheep slaughtering procedures 1 Survey of abattoir practice British Vet J 1402816 Gregory NG and Wotton SB 1984t Sheep slaughtering procedures III Headtoback electrical stunning British Vet J 1405705 Gregory NG and Wotton SB 1985 Poultry slaughtering procedures Paper 218 European Meeting of Meat Research Workers Albena Bulgaria pp 8791 Gregory NG Wotton SB and Wilkins LJ 1984 The effects ofinducing cartiac arrest at stunning on brain function bleeding ef ciency and susceptibility to bruising in sheep Paper 113 Proceedings 30th European Meeting of Meat Research Workers Bristol England pp 2526 Griffitha GL 1983 Proceedings of Technical Sessions World39s Poultry Science Assn Adelaide Australia Griffiths GL and Purcell DA 1984 A survey of slaughter procedures used in chicken processing plants Aust Vet J 6139940L Harris CE and Carter TA 1977 Broiler blood losses with manual and mechanical killers Poultry Sci 56182731 Heath D and Williams DR 1977 Man at High Altitude London Churchill Livingstone Heath GBS 1984a Slaughter of broilers Vet Rec 11598100 Heath GBS1984b The slaughter of broiler chickens World39s Poultry Sci J 4015 19 Heath GBS Watt DJ Waite PR and Ormond JM 1981 Observations of poultry slaughter Vet Rec J 1089799 Heath GBS Watt DJ Waite PR and Meakings PA 1983 Further observations on the slaughter of poultry British Vet J 13928690 Hoenderken R 1978a Electrical stunning of pigs for slaughter Why Hearing on Pre slaughter Stunning Kavlinge Sweden May 19 1978 Hoenderken R 1978b Electrical stunning of slaughter pigs Thesis State University Utrecht The Netherlands Hoenderken R 1983 Electrical and carbon dioxide stunning of pigs for slaughter In Eikelenboom G ed Stunning of Animals for Slaughter Boston Martinus Nijhoff pp 5963 Jensen JH Jul M and Zirck O 1978 Electrical stimulation of pig carcasses International Congress ofFood Science and Technology Abstracts p 124 Kirton AH and Frazerhurst LF 1983 Effects of normal light normal or double stunning on the incidence and severity ofbloodsplash in lambs Meat Sci 9 16 Kirton AH Frazerhust LF Woods EG and Chrystall BB 198081 Effect of electrical stunning method and cardiac arrest on bleeding ef ciency residual blood and bloodsplash in lambs Meat Sci 534753 Kotula A W ant Helbacka NV 1966 Blood volume of live chickens and the in uence of slaughter technique on blood loss Poultry Sci 456848 Kuenzel WJ Ingling AL Denbow MD Walther JH and Schaeffer MM 1978 Variable frequency stunning and the comparison of two bleedout time intervals for maximizing blood release in processed poultry Poultry Sci 5744954 Kuenzel WJ and Walther J H 1978 Heart beat blood pressure respiration and brain waves of broilers as affected by electrical stunning and bleedout Poultry Sci 576559 Kuenzel WJ no date Stunning killing and bleeding Specifications carcass quality and welfare concerns pp 63 Lambooy E 1981 Electrical stunning and meat quality ofveal calves 27th European Meeting of Meat 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