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During 2002, auditors working for McDonald’s, Burger King and Wendy’s evaluated 22 U.S. pork plants with the numerical scoring system. The data from these audits was compiled by the author. Ninety-five percent of twenty pork plants (19 out f 20) that used electric stunning placed the tongs in the correct location on 99% or more of the pigs. Two plants that used CO2 rendered 100% of the pigs completely insensible. Out of the 20 electric stunning plants, only one failed to render 100% of the pigs completely insensible. All of the electric stunning plants had either single file or double file races and a conveyor restrainer. One plant with group CO2 stunning had 0% electric goad use. Fourteen plants out of 22 plants (63%) used electric goads on 15% or less of the pigs and 3 (14%) used them on 16 to 25% of the pigs.
The performance of some plants is still poor. The author recently visited two pork plants and one used an electric prod on 100% of the pigs and the other failed to render sows insensible with a captive bolt due to poor gun maintenance. Handling and stunning was poor in several German and Spanish plants. Velarde et al. (2000) surveyed two plants with CO2 stunning where many pigs showed signs of return to sensibility. This was most likely due to overloading of the machine and insufficient exposure time in the gas. In a German plant, Schaffer et al. (1997) reported that 96.4% of the pigs were prodded with the electric goad at the entrance of the restrainer.
To reduce blood splashing (petechial hemorrhages) in the meat, some slaughter plants use high frequency stunning. However, too high of an electrical frequency of 2000 to 3000 hz failed to induce instantaneous insensibility (Warrington, 1974, Croft, 1952, Van derWal, 1978). Fifty cycles which is the regular mains electrical frequency was the most effective (Warrington, 1974). Anil and Mckinstry (1994) found that 1592 hz sine wave or 1642 hz square wave head only stunning at 800 ma induced seizure activity in small pigs. The main disadvantage is that at frequencies above 50 hz return to sensibility will occur more quickly (Anil and McKinstry, 1994). Due to kicking, high frequency head only stunning is not practical unless it is combined with an additional current to stop the heart. Eight hundred hz head only stunning in conjunction with a 50 hz current applied to the body is effective (Berghaus and Troeger, 1998; Lambooij et al., 1996 and Wenzlawowicz et al., 1999). This system is available in commercially built equipment.
Most plants in the U.S. apply a single current passed from the head to the body. It is essential to apply sufficient current to induce both cardiac arrest and an epileptic seizure. The author has observed large sows where sufficient current was applied to induce cardiac arrest but insensibility was not induced. In this situation, the sows had natural spontaneous blinking five seconds after stunning which later disappeared due to cardiac arrest (Grandin, 2001). Raising the amperage to greater than 1.25 amp eliminated blinking in sows. The blink looked like the blink of an unstunned pig and it was not rapid nystagmus.
Electrodes must be placed in the correct position to put the brain in the current path (Croft, 1952; Warington, 1974; Anil and McKinstry, 1998). Placing the electrodes too far back on the neck will result in a shorter period of insensibility (Velarde et al, 2000). Grandin (2001a) observed that placing the head electrode of a cardiac arrest stunner too far back on the neck resulted in blinking pigs. Placing the electrode in the hollow behind the ear eliminated the eye reflexes.
Electronic systems are now available to control amperage surges that cause petechial hemorrhages and monitor how well the operator applies the stunning tongs. Gregory (2001) monitored the electrical tracings of stuns to detect problems such as poor initial contact with the animal or interrupted stuns. He concluded that animal welfare problems occurred in about 9% of the stuns. Ross (2002) has developed an electronic microprocessor system that controls waveform, frequency and stun time. This computerized system also records operator errors that would compromise pig welfare such as interrupted stuns and energizing the electrode before it is in full contact with the pig. Unpublished data collected from these computers indicate that stunner operator errors due to fatigue greatly increase after 2 hours. Premature energizing of the electrode will cause squealing. Squealing is correlated with physiological indicators of stress (Warriss et al., 1994). White et al. (1995) reports that squealing is associated with discomfort.
Grandin (2001a) has found that problems with return to sensibility after electrical stunning can be easily corrected. The most common causes of problems with return to sensibility were wrong position of the tongs and poor bleeding technique (Grandin 2001a). Improving the ergonomic design of the head to back cardiac current stunning tongs or the employee’s work station, eliminated problems with return to sensibility.
Dutch research indicated that the excitation phase that occurs during CO2 stunning starts prior to the onset of unconsciousness (Hoenderken, 1983, 1978). This study raised the first questions of potential distress in pigs during the induction of CO2 anesthesia. However, research by Forslid (1987) indicated that unconsciousness occurred prior to the onset of the excitation phase; and CO2 stunning was not stressful. The research conducted by Anders Forslid at the Swedish Meat Research Institute had been on Yorkshire pigs (Anders Forslid Swedish Meat Resaerch Institute, Personal communication). In Yorkshire X Landrace crossbred pigs, exposure to CO2 was less aversive than electrical shocks from an electric goad (Jongman et al., 2000). Dodman (1977) reported that there was great variability on how pigs reacted to CO2. Grandin (1988) observed, in a commercial slaughter plant in the United States, that white crossbred pigs (with Yorkshire breed-type characteristics) had a much milder reaction to CO2 than black, white-striped crossbred pigs with Hampshire breed-type coloration.
Hampshire-type pigs rode quietly in the gondola until they first contacted the gas and then they reared up and violently attempted to escape. This occurred while they were fully conscious (Grandin, 1988a). Grandin (1994) observed that Danish pigs (which have a very low incidence of the Halothane gene) remained calm when they breathed CO2, but that Irish pigs (which have a high incidence of the Halothane gene) became highly agitated within seconds after sniffing the gas. More recent observations by the author in Denmark, of pigs that were free of the Halothane gene indicated that they remained calm after immersion in 90% CO2 until they collapsed and appeared to lose consciousness. There were no attempts by the pigs to escape from the container.
Experiments with Pietrain X German Landrace pigs indicated that Halothane-positive pigs had a more vigorous reaction to CO2 than Halothane-negative pigs (Troeger and Woltersdorf, 1991). These pigs had little or no reaction during initial contact with the gas; the reaction started about 20 seconds after the animals contacted the gas. Seventy percent of the Halothane-positive pigs had strong motoric reactions while only 29% of the Halothane-negative pigs reacted in this manner. Troeger and Woltersdorf (1991) expressed concern that reactions in Halothane-positive animals may possibly be of animal welfare concern but concluded that the use of high CO2 concentrations (80% or greater) reduced the incidence of vigorous reaction.
Human beings also vary in their reaction to CO2. People who have panic attacks, which has a strong genetic basis, will react very badly to CO2; the gas may induce panic attacks in these people (Griez et al., 1990; Bellodi et al., 1998). Raj and Gregory (1995) found that pigs exposed to CO2 were more reluctant to re-enter a box to eat apples than pigs exposed to argon. The pig breed used in this experiment was not specified. Research shows that 90% CO2 works the most effectively (Hartung et al., 2002). Hartung et al. (2002) found that in German pigs 80% CO2 was not sufficient to eliminate all reflexes after a 70 second exposure. They were also concerned abut the high catecholamine levels after stunning. Raj and Gregory (1995) reported that no escape attempts occurred at 80 to 90% CO2 but one out of six piglets attempted to escape at 40 to 50% CO2 and air. The use of a mixture of CO2 and argon gas may create an improved gas stunning system for pigs (Raj et al., 1997 and Raj, 1999). It is possible that a combination of CO2 and argon might make CO2 stunning less stressful for genetic types of pigs that react badly to CO2.
One welfare advantage of CO2 stunning is that CO2 systems can be designed so that lining pigs up in single file races can be eliminated. The pigs are moved into the CO2 chamber in groups of five. Handling pigs in groups makes quiet handling easier. Whereas cattle and sheep are animals that will naturally walk in single file, pigs resist lining up in a single file race (Grandin 2000b). Systems in which cattle and sheep are moved through single-file races work extremely well (Grandin, 2000).
In evaluating CO2 from a welfare perspective, one should look at the whole system. Eliminating single file races provides a welfare advantage and the trade off may be some unpleasantness during anesthesia induction. However, it is the author’s opinion that pigs attempting to escape from the container when they first contact the gas is not acceptable and genetic factors should be evaluated.
When head only reversible electric stunning is used, Hoenderken (1978) recommends bleeding pigs within 30 secs to prevent return to sensibility. However, Blackmore and Newhook (1981) recommends that they be bled within 15 seconds. Even when non-reversible methods are used, the author has observed that a few pigs may show signs of returning to sensibility. Stunning to bleed interval time is less critical when non-reversible stunning methods are used but effective bleeding is essential to insure that pigs showing signs of sensibility never enter the scalder. Grandin (2001a) found that improving bleeding so that the diameter of the initial blood stream was large prevented signs of return to sensibility after bleeding.
Research by Anil and McKinstry (1994) showed that in pigs stunned with reversible head only electric stunning, return to sensibility occurred in the following order: 1) rhythmic breathing, 2) corneal eye reflex, 3) respond to prick on the nose with a needle, 4) righting reflex to get up, 5) fully sensible. Danish researcher (Holst, 2001) found that return to sensibility after CO2 stunning occurred in the following order: 1) corneal reflex, 2) rhythmic breathing, 3) nystagmus (vibrating eye), 4) spontaneous natural eye blinking without touching the eye and 5) righting reflexes to get up.
At what point is this hierarchy of return to sensibility is the pig fully sensible and able to feel pain and other unpleasant sensations? Gregory (1998) states that a corneal reflex which is evoked by touching the eye can occur in both conscious and unconscious animals. If this reflex is absent one can assume that the animal is in a profound state of brain dysfunction and unconsciousness (Gregory, 1998).
Spontaneous blinking like a live animal would do in the lairage is at a higher level on the hierarchy of return to sensibility than a corneal reflex evoked by touch. It is likely that at this point the animal is sensible. The author has observed electrically stunned pigs getting up and walking around within 10 seconds after the appearance of spontaneous natural blinking.
When pigs are either hanging on the slaughter line or lying on a bleed table, the most common mistake is to misinterpret leg kicking as a sign of sensibility. In electrically stunned pigs it is normal to have kicking. The presence of the classic tonic and clonic spasms is a sign of an effective electrical stun that has induced an epileptic seizure (Croft, 1952). The rigid tonic phase is followed by kicking (clonic phase). Gregory (1998) states that a completely relaxed jaw is a good indicator of brain dysfunction and unequivocal unconsciousness. When this occurs the tongue will be flaccid and extended. The one reflexive movement that is difficult to abolish is gasping, it is a sign of a drying brain (Gregory, 1998).
The righting reflex looks different when a pig is hanging on the rail. A properly stunned pig regardless of stunning method will hang on the rail with a straight back and flaccid head (Grandin, 2001a). When a righting reflex occurs, the neck and lower back arch and stiffen as the animal attempts to lift up its head. Some fully sensible pigs will curl their heads forward towards their forelegs.
The author has observed that misinterpretation of eye reflexes in electrically stunned pigs is a problem especially when untrained people poke at the eye. Eyelids that are stuck closed with mucous can suddenly open and look like a reflex (Grandin, 2001a). Under commercial conditions, both Grandin (2001a) and Holst (2001) agree that spontaneous natural eye blinking without touching the eye must be absent at all times after stunning. It is an easy sign to observe and it is less likely to be misinterpreted (Grandin, 2001a; Holst (2001). Natural spontaneous blinking is never acceptable but a maximum of 5% of CO2 stunned pigs can have a corneal reflex evoked by touch (Holst 2001). Nystagmus (vibrating eye) must not be confused with natural blinking and this will occur in some pigs stunned correctly with electricity.
Both at the slaughter plant and at the farm loading trucks, people must understand the basic behavioral principles of animal handling such as flight zone and point of balance (Grandin, 1987). Calm pigs are easier to move and sort than excited agitated pigs. Another principle is to move small groups of animals and to fill the forcing pen that leads up to the single file race half full (Grandin, 2000b). Animals will also move more easily up a single file race or truck-loading ramp if they walk without stopping through the forcing pen. Pigs left standing in a forcing pen are more likely to turn around.
Electric goads should be replaced as much as possible with other non-electric driving aids. Pigs moved with electric goads have a higher heartrate than pigs moved with a panel (Brundige et al., 1998). A study by Benjamin (2001) indicated that prodding pigs multiple times with electric goads results in a significant increase in the number of stressed pigs that became non-ambulatory. Electric goads also increased body temperature and blood lactate (Brundige et al., 1998). Some effective non-electric driving aids are panels, plastic paddle sticks and a large flag made of light weight plasticized cloth (Grandin, 2000b). Small groups of calm pigs can be easily moved with these driving aids.
Both research and practical experience shows that pigs have a tendency to move from a dark place to a brighter place (Van Putten and Elshof, 1978; Grandin, 1982, 1996 and Tanida et al., 1996). Installing a light at the entrance of a restrainer can improve pig movement and reduce electric prod usage (Grandin, 1996). Animals will also balk and back up if air drafts are blowing towards them as they approach a race or restrainer entrance. A calm pig will look right at the distraction that attracts its attention (Grandin 2000b). Quiet handling of pigs will be impossible until all the distractions are found and eliminated. Another common distraction is seeing people or moving machinery up ahead. Solid sides on races and shields can help block these distractions. Pigs will also balk at sparkling reflections on a wet floor or shiny metal. Sometimes all that is required is to move a light on the ceiling to eliminate a reflection (Grandin, 1996; 2000b). Schaffer et al. (1997) reported that in one plants pigs refused to enter a restrainer and 96.4% had to be shocked with an electric prod. It is the author’s opinion that eliminating a few small distractions may improve pig movement in this plant. People need to get down to the pig’s level and see what the pig is seeing. A reflection that the pig sees may not be visible to a standing person. Another problem is seeing the visual cliff effect under a conveyor restrainer that is elevated off the floor. Animals can perceive depth (Lemman and Patterson, 1964). Installation of a false floor under a restrainer can facilitate animal entry (Grandin, 1996, 2001b).
When new plants are built, consideration should be given to reduce noise. After visiting many plants, the author has observed that lairage areas with high ceilings and pre-cast concrete walls have more echoes and noise than plants built from metal clad foam core insulation panels (Grandin, 2000b). The author visited a plant with pre-cast concrete walls and the sound level was 88 dB in the lairage and 93 dB at the restrainer. The pigs were quiet and all the equipment was running.
Information on the layout and design of races and lairages for slaughter plants can be found in Grandin (2000b, 1990; Barton-Gade and Christianson, 1993). The use of long narrow lairage pens is recommended (Grandin, 1980, 2000b). Long narrow pens increase the fenceline length in relation to the floor are and may help reduce fighting. Pigs prefer to lie along the fence (Stricklin et al., 1979). Nonslip flooring is essential. The author has observed that slick floors are a common cause of animals falling and other welfare problems during handling. Non-slip flooring is essential.
A single file race must never be bent sharply where it joins the forcing pen. The pigs will refuse to enter because they see no place to go. A paper by Weeding et al. (1993) shows a poorly designed single file race and pigs handled in this system had increased stress. Pigs will jam in a funnel-shaped crowd pen leading up to a single file race. A pig race must have an abrupt entrance. Further ifnrmation of crowd pen design for pigs is in Grandin (1982, 2000b) and Hoenderken (1976).
The design of conveyor restrainers will also affect welfare. The author has observed that heavily muscled pigs are not well supported in traditional conveyor restrainers. The new center conveyor restrainers that a pig straddles supports heavy muscle pigs better. Information on these restrainers can be found in Giger et al. (1977), Grandin (1988, 2000b, 2003). These systems are now commercially available. Pigs should enter the restrainer easily. If they refuse distractions and should be located and removed. A reasonable level of performance is 85% of the pigs should enter without the need for an electrical goad (Grandin, 1998).
British researchers have reported that pigs from certain farms are more difficult to drive (Hunter, et al., 1994). Geverink et al. (1998C) reports that pigs that have been walked in the aisle during finishing will be easier to drive. Moving pigs out of the finishing pens a month prior to slaughter also improved their willingness to move (Abbott et al., 1997).
Pigs from certain lean genetic lines may be more excitable and difficult to drive (Grandin, 1987). Shea-Moore (1998) found that high lean pigs were more fearful and explored an open arena less than a fatter line of pigs. Lean line pigs also got into more fights after mixing (Buss and Shea-Moore, 1999). More time was required to move lean line pigs down an alley compared to a fatter line of pigs. Work with producers by the author has shown that excitability can be reduced and the pigs will be easier to drive if the producers walk through the pens every day (Grandin, 2000b). This is especially important for pigs from excitable genetic lines. Grandin et al. (1984) found that people walking in the pens or allowing pigs to walk in the aisles produced pigs that were more willing to walk through a chute (race). The author recommends that every day the producer should walk through both grower and finishing pens to teach the pigs to quietly get up and flow around him. Pigs differentiate between a person in the aisle and a person in their pens.
Another factor which may increase both handling and potential welfare problems is feeding pigs the repartitioning agent ractopamine to make pigs leaner. Marchant-Forde et al. (2002) reported that pigs fed 10 ppm had higher heartrates during handling and higher epinephrine levels. The authors conclude “the results show that ractopamine does affect the behavior and physiology of finishing pigs and may make them more difficult to handle and more susceptible to handling and transport stress” (Marchant-Forde et al., 2002).
One of the most important factors which determines if a pig is fit for transport is the condition of the pig that is loaded onto the truck. Cull sows should be marketed when they are still fit for travel. Sows and pigs that are unable to walk should be euthanized on the farm. Stressor pigs which have temporarily become non-ambulatory must be allowed to recover before they are put on a truck. A combination of genetic selection for leanness and poor management has resulted in increased sow mortality (Koketsu, 2000). Interviews with producers by the author indicated that leg problems are a large contributor to these sow losses and transporting lame sows may cause welfare problems. Producers and breeders need to select sound animals with good feet and legs. Recently the author has observed that some slaughter weight pigs are land and have poor conformation of the feet and legs.
The presence of the stress gene will increase death losses during transport. Murray and Johnson (1998) found that 9.2% of the pigs that were homozygous positive for the stress gene died during transport. Death loss percentages were 0.27% in heterozygous stress gene carriers and 0.05% in pigs that were stress gene free. Fortunately many producers are now selecting pigs that are stress gene free to improve meat quality. A survey of pigs arriving dead on arrival at the slaughter plant indicated that deads decreased from 0.27% to 0.1% when the stress gene was removed (Holtcamp, 2000).
The author has observed that small piglets can get dew claw injuries when they go down a ramp designed for slaughter weight pigs. The animals slip and damage their dewclaws. To prevent injuries to young piglets small closely spaced cleats are required. Further information on the design of loading ramps can be found in Grandin (1987, 1990, 2000b).
There is evidence that travel in a vehicle is more stressful than just being loaded onto a stationary truck for the same amount of time. After a 25 minute ride or a stationary wait in a truck Geverink et al., (1998) reported that after unloading the pigs that were actually transported were less active and spent less time exploring their environment. Salivary cortisol was significantly higher in the transported group (Geverink et al., 1998).
Further research is needed to determine if uncomfortable vibration is the reason why pigs remain standing on short journeys. Maybe they lie down when they get too fatigued to stand any longer. This question needs to be answered to determine if pigs need enough room to lie down on short journeys.
For both meat quality and welfare reasons, pigs should be rested for 2 hours before slaughter (Milligan et al., 1998). The author’s observations of thousands of pigs indicate that pigs moved to the stunning area immediately after unloading were much harder to handle and more electric goad use was required to move them than pigs that were rested for a minimum of one hour. Perez et al. (2002) found that either no lairage time or an excessively long lairage time compromised both welfare and pork quality. Leheska et al. (2002) report that long transport times reduced PSE and improved pork quality compared to short transport times of 30 minutes. They also found that fasting for 48 hours improved pork quality. The author is concerned about the welfare implications of a 48 hour fast.
Many plants shower pigs in the lairage to reduce PSE. Sometimes pigs were showered during very cold weather which was probably detrimental to their welfare. Knowles et al. (1998) reports that pigs should not be showered continuously when the temperature is below 5 degrees C and showering should stop when pigs shiver.
Brown et al. (1999) found that pigs from one farm fought more than pigs from another farm. If pigs do fight the stress of mixing and being driven down an alley is greater than either stressor singly (Geverink, et al., 1998). From a welfare standpoint, it is the author’s opinion that monitoring skin damage is a good way to monitor welfare problems from fighting. This may be a better approach than specifying that pigs should never be mixed.
Handling during loading of pigs can be scored with a similar scoring system. Drivers could be scored on death losses, the percentage of pigs that fall down during driving and electric goad use. In conclusion, holding people accountable for losses and the use of numerical scoring systems will help managers to maintain high standards.
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