ST. PAUL, Minn. -- One of the first steps in humane slaughter is immobilization of the bird. This involves the stunning process, and although stunning prior to slaughter is not required by law for poultry in the U.S., stunning practices are used widely in the poultry industry in the U.S. and worldwide.
Electrical stunning using low voltage is the primary stunning method used in the North American poultry industry while electrical stunning using high currents and gas stunning are popular methods used in the European poultry industry.
However, there is an increasing number of processing plants, especially turkey plants, in the U.S. that are using or have plans to use gas stunning systems. Stunning birds with either electricity or gas effectively and humanely immobilizes birds and also provides additional benefits such as better cut efficiency, better bleedout and better quality.
Electrical stunning
Electrical stunning has been the primary method of stunning in the U.S. poultry industry. In this type of system, birds are typically hung on shackles and then come in contact with an electrical current that is delivered via a saline solution and metal grate. The electrical current flows from the charged saline solution through the bird and to the shackle which serves as a ground.
As a result of the current, the wings contract and tuck into the body and the neck arches, allowing the birds to enter the cutting machine properly for better cut efficiency (Rawles et al., 1995; Sams, 2001). Also, due to minimization of struggling during the cutting and bleed-out process, the heartbeat and blood pressure are stabilized allowing for a better bleed-out (Wabeck, 1987).
In the U.S., low amperage/voltage system parameters are typically 10-25V and approximately 20 mA (up to 40mA) for approximately 10-12 seconds for turkey stunning. In contrast, high voltage/amperage (e.g., 150 mA, 4-7 sec, turkeys) systems are used in Europe due to regulations for irreversible stuns. The low voltage/amperage reversible stunning methods which are used render the birds unconscious for a period of approximately 60 to 120 seconds, depending on amperage used (Rawles et al., 1995; Sams, 2001).
However, birds are cut and bled within a short period, 7-10 seconds, following stunning and therefore, birds do not recover as they have lost a sufficient amount of blood before recovery could happen. In the high amperage stuns, the birds are basically electrocuted and undergo cardiac arrest, and therefore, do not recover (Sams, 2001).
However, they are still cut within a short period of stunning. A major disadvantage of the high amperage stuns is that they can cause considerable carcass damage resulting in lower yields. Carcass damage can also result from a low amperage stun if done improperly.
Electrical stunning is an effective method of immobilizing birds for slaughter. However, the system must properly be managed. Even when using low amperage stuns, birds can be improperly stunned if the parameters are set too low or too high, or if the equipment is improperly adjusted. Improperly stunning birds can result in carcass damage including broken wings, broken clavicles, hemorrhages in the breast and thigh, ruptured capillaries (blood splash) in the breast, and red wing tips as well as a poorly bled bird (Wabeck, 1987; Rawles, 1995).
These are the same quality problems that can occur when stunning using the high amperage European models. The hemorrhages in the breast can especially be problematic because of the high use of turkey breast meat in further processed products. A blood spot in a deli loaf can be a major issue for consumer acceptance.
Another condition that may be considered a disadvantage of electrical stunning is that birds are shackled on the processing line in a live state. This has received much attention lately due to animal welfare concerns. However, it is important to note that electrical stunning systems are instantaneous and effective methods of immobilization and humane slaughter. However, with these disadvantages in mind, some processors have considered the use of gas stunning, or controlled atmosphere stunning. Gas stun systems generally bypass the step of hanging a live bird because the hanging step occurs after the stunning process when the birds are no longer conscious and therefore minimize handling of the live bird.
Gas stunning
Gas stunning, or controlled atmosphere stunning (CAS), is another option to use for stunning poultry. Gas systems have used gases that displace oxygen (e.g., argon, nitrogen) or gases that directly affect the central nervous system (e.g., carbon dioxide) (Gerritzen et al., 2000). Carbon dioxide can produce rapid unconsciousness by altering the pH of the cerebrospinal fluid or anoxia at high concentrations (Sams, 2001).
Other gases, such as argon, produce unconsciousness due to lack of oxygen to the bird (Sams, 2001). With the reversible system, carbon dioxide is combined with air and birds are stunned over approximately a 25 second period resulting in a loss of consciousness for approximately 60 seconds (Kang and Sams, 1999). In irreversible stun systems (i.e., stun-to-kill) where birds do not regain consciousness, carbon dioxide, dioxide, and nitrogen are generally used at an exposure time of 2-3 minutes.
In Europe, argon is also used, but it is too expensive for use in the U.S. In the initial phases of carbon dioxide stunning, lower concentrations of carbon dioxide are used because although carbon dioxide is an anesthetic gas, it is also an irritant. Higher levels of dioxide may also be used in this phase to reduce the irritating effects. In the later phases of stunning, higher concentrations of carbon dioxide (50-80 percent) are used in order to produce an adequate stun.
In the U.S., there are a few systems available and/or are in use, and these are primarily carbon dioxide based systems. However, the use of gas stunning is increasing in turkey plants in the U.S. due to animal welfare concerns, customer specifications, meat quality and labor issues. These newly implemented systems are generally stun-to-kill (irreversible) systems where the birds do not recover from the stun.
The systems vary in set up, but generally birds are stunned before they are hung on the shackle line. Therefore, birds are directly placed onto a conveyor belt or left in crates, though this requires individual crates to be used in transportation and this is not always the case in the U.S. Birds are then conveyed through a tunnel where they are subjected to the mixture of gases. The period of time in the tunnel varies depending on the concentration of gases used and for how long, but in an irreversible stun, two to three minutes is typical.
Following the stun, the birds are hung on shackles and then move to the cutting machine. This is a benefit to the worker who is hanging the birds since the birds are in a relaxed state. It is also beneficial to the resulting meat products since damage that could normally result from hanging birds in a live state (i.e., bruising, broken wings, etc.) is significantly reduced.
Another system that has recently been developed and implemented by a few turkey processors is an on-truck stunning device. Because birds are typically transported in modules on trucks in the U.S., this system works well with existing transportation equipment/vehicles and is relatively easy to install. In this system, a device surrounds a section of a truck and then delivers the mixture of gases (carbon dioxide based) in multiple stages.
Following the stun period, birds are unloaded from the truck and hung on shackles. Because the birds are inactive, the hanging process is much easier on workers. Quality can also be improved due to hanging birds in an unconscious state. However, in this system, there can be a longer time between stun and cutting (bleed-out) due to the amount of time required to unload the truck, especially for the last birds unloaded after stunning. While sufficient blood loss can still occur, this extended period can result in poor picking; therefore, scalding and picking equipment may need adjustment for acceptable feather removal.
Implementation of gas stunning systems has increased in turkey processing plants in recent years. In 2008, O'Keefe (2008) reported that eight U.S. turkey processing plants had gas systems in comparison to only one broiler plant. This increased interest in implementing gas stun systems is because there are benefits to using these systems for stunning turkeys, especially with the large toms. Additionally, animal rights groups have placed pressure on retail and foodservice groups for this implementation of gas stunning for turkeys, leading to increased customer requests for the process.
The ergonomics of hanging birds have improved (reduced labor demands) and this can result in more yield due to more pounds per man hour hung (O'Keefe, 2008). Because the birds are no longer handled live at the processing plant (i.e., not hung on shackles), animal welfare issues have been addressed and quality defects (e.g., bruises, broken bones) have been reduced. Furthermore, the low percentage of quality defects arising from electrical stunning (e.g., hemorrhages, blood splash) has also been reduced. This is especially a benefit when processing large toms because these birds are used primarily for further processing.
Reduction in defects can improve quality and increase yield. Though there are benefits of gas stunning, there can also be drawbacks. There is a high capital cost as well as operating costs (gases) of these systems, relative to electrical stun systems. Also, the footprint required can be large for in-plant systems. Regardless, in most cases, the benefits outweigh the drawbacks, especially when processing large turkeys.
Dr. Casey M. Owens is an associate professor with the University of Arkansas' Center of Excellence for Poultry Science. This article is drawn from a presentation given at the Midwest Poultry Federation Convention in St. Paul, Minn.
For further information, please call Poultry and Egg News at 770-536-2476 to subscribe.
Current News