Recent Advances in Electrical Stunning

Transcription

1 Recent Advances in Electrical Stunning S. F. BILGILI1 Department of Poultry Science, Auburn University, Auburn, Alabama ABSTRACT This paper provides an overview of the within the context of differing slaughter technologies, electrical stunning systems and their implementation in practices, and regulatory constraints. Finally, the impact modern-day broiler slaughter plants. The application of of electrical stunning on traditional carcass and meat low voltage electrical stunning systems in the U.S. is quality attributes of broilers is examined. reviewed and contrasted with European experiences (Key words: electrical stunning, slaughter, carcass quality, broiler) INTRODUCTION Electrical stunning is the most universally accepted and utilized method for immobilizing poultry prior to slaughter. The equipment is relatively simple, inexpensive, takes up little space, is compatible with the current kill-line speeds, and for the most part, is easy to operate and maintain. Electrical stunning systems for poultry were primarily developed to render the bird unconscious long enough to allow automated neck cutting and to reduce carcass damage due to slaughter-induced struggle and convulsions during bleeding. Although considered more humane than killing without stunning, electrical stunning has often been questioned, especially in Europe, on animal welfare grounds (Fletcher, 1993). In contrast to European recommendations, which require specific conditions to assure that poultry be instantaneously rendered insensible to pain until death supervenes (Kettlewell and Hallworth, 1990), the Poultry Inspection Regulations do not mandate stunning conditions in the U.S. (USDA, 1984). Regardless of differences in cultural, religious, and regulatory practices governing slaughter of poultry, the application of electrical stunning principles in slaughter plants and the effects of stunning-killing on end-product quality are of concern to processors worldwide. Excellent reviews have been published on electrical stunning basics (Richards and Sykes, 1967; Ingling and Kuenzel, 1978; Kuenzel and Walther, 1978; Schutt-Abraham et al., 1983; Veerkamp and de Vries, 1983; Gregory, 1989; 1999 Poultry Science 78: Kettlewell and Hallworth, 1990; Bilgili, 1992a) and slaughter-bleeding of poultry (Newell and Shaffner, 1950; Davis and Cole, 1954; Kotula and Helbacka, 1966; Abram and Goodwin, 1977; Scott, 1978; Heath et al., 1981, 1983; Heath, 1984; Warris, 1984). The scope of this review will be to highlight the recent advances in design and application of electrical stunning technology in modern-day broiler slaughter plants. PRINCIPLES OF ELECTRICAL STUNNING Electrical stunning is accomplished by passing a sufficient amount of electrical current through the central nervous system of birds for a given amount of time (Bilgili, 1992a). The state of unconsciousness induced by electricity results from the inhibition of impulses from both the reticular activating and the somatosensory systems (Heath et al., 1994). Loss of somatosensory evoked potentials (SEP) and spontaneous electroencephalograms (EEG) have been directly related to brain failure and instantaneous insensibility to pain (Richard and Sykes, 1967; Lopes da Silva, 1983; Gregory and Wotton, 1989, 1990). The stunning current reaching the brain must be adequate enough to induce an epileptic seizure. This current is usually lower than that required for ventricular fibrillation and, hence, death by electrocution. Insufficient currents may physically immobilize the bird, but may not prevent perception of pain, stress, or discomfort by the animal. Hence, if the bleeding is not rapid, birds may regain consciousness prior to scalding (Fletcher, 1993). Received for publication August 5, Accepted for publication July 23, To whom correspondence should be addressed: sbilgili@acesag. auburn.edu Abbreviation Key: EEG = electroencephalograms; NELS = New Enhanced Line Speeds; SEP = somatosensory evoked potentials; SIS = Streamlined Inspection System. 282

2 Stunning Equipment and Electrical Circuits SYMPOSIUM: RECENT ADVANCES IN SLAUGHTER TECHNOLOGY 283 Although there are many makes of commercially available electrical stunners, for the most part their design and operation are similar. A fiberglass brine-water bath cabinet is supported under the overhead conveyor line from which chickens move suspended on shackles. The cabinet is vertically adjustable and usually set at a height that allows the heads of the birds to be submerged in brine-bath water. An electrified metal grate is submerged in the bottom of the brine-water bath tank. Although the shackle line is connected to earth, a ground bar contacting the shackles is often used to complete the electrical circuit. The birds pass through the stunner cabinet in a continuous procession, typically either 140 or 180 birds per minute in the U.S., depending upon the inspection system used. When a voltage is applied between the submerged electrode and the earth (ground), the current flows through the immersed chickens in the cabinet to complete the circuit. Chickens in this type of circuit represent a series of resistors connected in parallel. Although birds contacting each other in this circuit can create other resistive pathways, the significance of these pathways is not well established (Kettlewell and Hallworth, 1990; Sparrey et al., 1992). The amount of current that flows through each individual bird is dependent upon the voltage applied and the electrical impedances of the birds in the brinewater bath. Woolley et al. (1986a,b) have shown that whole bird resistance of broilers ranges between 1,000 to 2,600 V. More recently, sex differences in resistance were also reported, with females exhibiting higher resistance than males (Rawles et al., 1995). As the birds enter and leave the stunner cabinet, they constantly change the total resistance of the system. At a given constant voltage, the birds receive a current in proportion to their own resistance. In addition, the resistance provided by the water or brine solution is also critical and has been shown to vary under commercial conditions (Bilgili, 1992a). Commercial stunners provide a choice of alternating or direct currents, either low or high frequency, half or full rectified, sine or square waveforms, constant or pulsed currents (Ingling and Kuenzel, 1978; Griffiths and Purcell, 1984; Bilgili, 1992a; and Heath et al., 1994). The effectiveness of an electrical stunning system is dependent upon not only the electrical variables used (i.e., current, voltage, waveform, frequency, and duration), but also the biological factors that affect bird impedance (i.e., size, weight, sex, composition, and feather cover) (Kettlewell and Hallworth, 1990). Woolley (1986a,b) has shown that individual birds, as well as different tissues within a bird, vary in their resistance. Given the typical biological variation observed among the birds within or between the flocks processed, it is not surprising that the research and development of stunning technology have been driven primarily by defining and standardizing the electrical variables used in stunning. Overview of Stunning and Slaughter Practices It is important to emphasize that stunning, neck cutting (killing), and bleeding operations are inseparable and interrelated steps in the slaughter process. The evolution of electrical stunning technology in modern-day broiler plants, for the most part, has been driven by other factors in the slaughter process, such as type of neck cut performed, bleed time, scalding and picking efficiency, and extent of automation in evisceration. In this context, it is important to highlight the varying commercial practices in the stun-slaughter process. Kill line speeds are dictated by the number and speed of evisceration lines in the U.S. Typically, each kill line supplies carcasses for two evisceration lines. Depending upon the inspection system utilized, evisceration line speeds are limited to either 70 or 91 birds per minute, for the Streamlined Inspection System (SIS) or New Enhanced Line Speeds (NELS), respectively. A U.S. plant with four NELS evisceration lines will typically operate two kill lines, each at 180 birds per minute, which is in contrast to European plants, in which each evisceration line is served by a separate kill line, usually operating at 100 to 140 birds per minute. The kill line speeds are important in terms of dwell time in the stunner (i.e., length of the stunner cabinet), as well as efficiency of kill and bleeding operations. In the U.S., the blood vessels within the neck of the bird (both carotid arteries and jugular veins) are severed usually by a deep ventral cut within 8 to 12 s of stunning. This methodology is accomplished by automatic neck cutters and by back-up personnel (Heath et al., 1994). The ensuing rapid drainage of blood causes anoxia and often prevents birds from regaining consciousness during the subsequent 80 to 90 s bleed time. In Europe, the neck cut is performed dorso-laterally or on one side only. Because the rate of blood loss is slower, the bleed times are usually extended to 120 to 180 s. This type of cut often leaves major blood vessels that supply the brain intact, giving birds the opportunity to regain consciousness when the cut or bleeding is incomplete (Gregory, 1992). This potential for regaining consciousness has been the major reason from the humane standpoint that current levels of 120 to 150 ma per bird have been suggested in Europe to insure an instantaneous and irreversible stun, i.e., stun-to-kill (Fletcher, 1993). Contrasting with Europe, the electrical currents used in the U.S., have been traditionally much lower (25 to 45 ma per bird). Also, the deep bilateral neck cuts often severe the trachea and cause the heads to come off in the pickers. Concern over the removal of a section of trachea that is usually left attached to the neck has prevented many processors in the Europe from using deep ventral neck cuts in the past. Recently, new evisceration systems have been approved in the U.S., wherein the viscera are completely removed from the carcass during evisceration and inspection (Bilgili, 1997). These systems operate at

3 284 evisceration line speeds of up to 140 birds per minute. Because the transfer from kill to evisceration shackles is automated with these new systems, each evisceration line is supplied by a separate kill line, operating at similar line speeds. The two systems currently being used, Nu-tech2 and Maestro,3 both utilize automated kill machines to severe the neck on one side, leaving the trachea and esophagus intact. The bleed time is extended to 150 s, as the rate of blood loss is reduced. Both systems require specialized head pullers to separate the head together with trachea and some crops. This separation of head, crop, and trachea is a crucial step in these total evisceration systems, whereby the visceral organs are loosened for later separation by the specialized eviscerators. Recent Advances in Electrical Stunning Systems There have been significant advances in electrical stunning systems in the last few years. Development and implementation of low voltage (10 to 14 V, Pulsed direct current, 500 Hz, 10 to 12 ma per bird) stunning systems for broilers has been well received by the industry (Wayne Austin, 1997, Simmons Engineering Co., Dallas, GA, 30132, personal communication). This low level of stunning has been accomplished by significant changes not only in electrical circuitry, but also in the actual stunning process. The most significant change has been the lengthening of the stunning cabinets, from 6 to up to 14 ft (1.8 to 4.3 m), in an attempt to increase dwell time and to reduce the total resistance in the stunner. The cabinets are designed with rump-bars to limit the movement of the birds and to prevent birds from avoiding the brine-bath. Overflow of charged brine at the entry end of the cabinet is eliminated by elevating a secondary entry ramp. This secondary in-feed ramp is extended 4 to 5 cm over the primary ramp to allow quick capture of birds at entry into the brine solution. Breast rub pads are utilized industrywide to calm the birds from live-hanging through the stunning. The feet-shackle contact is sprayed with water or brine solution to assure current flow. The metal grate at the bottom of the stunner cabinet is immersed roughly 1 cm in brine solution (1% NaCl recommended) at the entry end of the cabinet. More importantly, ground bars are designed to assure continuous and uninterrupted flow of current through the system. The stunner control panels have also been redesigned for continuous display and monitoring of the voltage and current levels. The popularity of low voltage electrical stunning in the U.S. is evident in a survey published by Heath et al. (1994). Of the 329 poultry plants surveyed in the U.S., 92.1% utilized electrical stunning as the method of preslaughter immobilization. Low voltage (10 to 25 V) and high 2Stork Gamco Inc., Gainesville, GA Cantrell-Meyn, Gainesville, GA BILGILI frequency (500 Hz) systems were used in 77.4% of these plants. Such low voltage is in contrast to high voltage and current systems utilized in Europe and other parts of the world. By design, all the communal brine-bath stunning systems suffer from the same fundamental constraint in that many birds are connected to the same circuitry at the same time. In such systems, theoretically the current levels experienced by individual birds cannot be controlled. Several attempts have been made in recent years to design constant current stunners for broilers. The electrical circuitry is available to measure the resistance of individual birds and meter the desired current (Rawles et al., 1995). However, the application of these systems in commercial slaughter lines has been limited. On the kill line, the birds are suspended on shackles approximately 15 cm apart. Given the commercial kill line speeds, it is extremely difficult, if not practically impossible, to isolate each bird long enough to measure its resistance and deliver precisely the preset current. Electrical Stunning and Product Quality The quality of end-products, whether whole birds, parts, or boneless-skinless meat, is of great importance to the processors. Bruising, discolorations, and broken or dislocated bones are the primary defects often attributed to the stunning-bleeding stage of slaughter (Bilgili, 1992a). Application of high voltages during stunning has been associated with broken bones (Gregory and Wilkins, 1989), exploded or damaged viscera, bruised wing joints, and red wing tips (Heath, 1984), hemorrhages on the breast meat (Veerkamp and de Vries, 1983; Veerkamp, 1988), and split wishbones and separation of shoulder muscle tendons (Sams, 1996). Under commercial conditions, it is extremely difficult to isolate the effects of electrical stunning from that caused by other factors, such as catching, hanging, wing flapping, type of cut, efficiency of bleeding, and picking (Gregory et al., 1989; Gregory and Wilkins, 1993). Although there is no clear relationship between stunning current and the traditional whole carcass quality attributes (Griffiths, 1985; Bilgili, 1992b,c), hemorrhages on deep breast muscles of broilers have been shown to increase with high stunning currents (Veerkamp, 1988; Gregory and Wilkins, 1989). On the other hand, high stunning voltages have been linked to increased incidences of red wing tips and tails (Veerkamp and de Vries, 1983) and broken bones (Walther, 1991). High stunning current frequencies have been shown to reduce the severity of thigh and breast hemorrhages, and result in fewer broken bones (Gregory et al., 1990; Hillebrand et al., 1996). It has been postulated (Veerkamp, 1992; Bilgili, 1993) that causes of muscle hemorrhages in broilers were multifactorial and may involve factors related to live production. In a recent study (Kranen et al., 1996), the extent of disturbances in blood circulation created by low rearing temperatures did not

4 SYMPOSIUM: RECENT ADVANCES IN SLAUGHTER TECHNOLOGY 285 correlate with occurrence of hemorrhages in breast and thigh muscles. In the same study, whole-body stunning caused more severe hemorrhages than head-only stunning. SUMMARY The electrical stunning systems currently being used in modern-day broiler slaughter plants have evolved in response to regulatory, as well as technological changes, in processing technology. Low voltage electrical stunning systems have been an effective method for immobilizing broilers prior to slaughter in the U.S. Personal observations in commercial broiler processing plants indicate that traditional whole carcass defects often attributed to stunning damage arise only in the presence of day-to-day operational problems. With the expansion of further-processed poultry products in recent years, there has been a renewed interest on the influence of electrical stunning on endproduct quality. 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