Regardless of which type of stunning is used, when properly monitored, maintained, and operated each system is effective and humane for the slaughter of poultry. These best management practices for poultry stunning should be considered as a guide for achieving the best outcomes.
Best practices
Stunning is done to render the bird unconscious prior to the neck cut and death. Unconsciousness eliminates the potential pain of the cut and positions the bird for proper, automated cutting. The two main types of stunning used in the poultry industry are electrical and controlled atmosphere stunning (CAS).
From arrival until scalding, close attention should be paid to the equipment and the animals in order to ensure the best possible meat quality and animal welfare. Once birds arrive at the processing plant, they need at least 30 minutes but no more than two hours of rest in lairage. There, protect them from the elements and provide the necessary climate controls.
Electrical stunning
In electrical stunning, birds are hung from shackles, then passed through a stunner bath filled with an electrified brine. The current passes through the brain and body rendering unconsciousness.
In the U.S., birds are stunned using low voltage. This renders unconsciousness but does not stop the heart. In the European Union, birds are stunned using high voltage which renders unconsciousness and stops the heart.
High-voltage stunning prevents the recovery of consciousness if the neck cut misses, but it can diminish meat quality through hemorrhages and broken bones caused by severe muscle contractions. Low-voltage stunning minimizes these meat quality defects and does not kill the bird, which is required for some religious slaughter practices. Low-voltage stunning is always part of a two-step process, too, because of the potential recovery of consciousness.
High-voltage stunning prevents the recovery of consciousness if the neck cut misses, but it can diminish meat quality through hemorrhages and broken bones caused by severe muscle contractions. | (Dianna Bourassa)
Shackling
Following lairage, birds enter the plant for shackling. In systems where birds are tipped for removal from their transport module, a separate slide should be available for the upper levels to minimize the distance from the module door to conveyor belt. Additionally, watch the modules and ensure no birds get stuck, or hung up, preventing normal removal. Systems using drawers or trays allow for shackling directly from the transport container.
In the hanging room, the environment is important for the animals and the workers. Low levels of light, often shaded blue, will minimize bird stress while allowing hangers to see and work. Minimize loud noises and extreme temperatures in this area.
Before entering the electrical stunner, the shanks of the bird at the shackle should be sprayed with a saline solution. | (Dianna Bourassa)
Handle birds with care when shackling. Lift and shackle birds holding a leg in each hand. Ensure the shackles are the right size for the bird, too. If they are too small, the bird will either be pinched by the shackle or it will be unproperly seated and less likely in the right position for stunning and slaughter. Only one bird should be placed into each shackle with only one leg per side.
Do not skip shackles, as this will increase the level of electrical current passed through each bird if the electrical parameters are set based on a bird in every shackle. Do not shackle dead on arrival (DOA), sick, injured or cull birds and, if necessary, immediately euthanize them.
There are ways to minimize stress on the birds, and potential meat quality defects, during this process. Minimize the time and distance between shackling and stunning. Keep lighting low. Avoid abrupt turns, dips or bumps on the path to the stunner. A breast bar of appropriate size for the birds can be added to give a supportive or calming effect.
The stunner bath
Before entering the electrical stunner, the shanks of the bird at the shackle should be sprayed with a saline solution. The brine in the solution should be a concentration of 1 gram of salt per liter of water or higher. The saline solution greatly enhances conductivity for proper stunning. When entering the stunner, the head should be the first thing to touch the water.
Pre-stun shock occurs when another part of the bird, like the shoulder or wing, contacts the water bath first. Avoid this by using an entry ramp that is electrically isolated from the water bath. This prevents water from overflowing at the entry point. The shackle line must be configured so birds are drawn up the entry ramp allowing the head and neck to contact the water first.
Pre-stun shock occurs when another part of the bird, like the shoulder or wing, contacts the water first. Avoid this by using an entry ramp that is electrically isolated from the stun bath. | (Dianna Bourassa)
Moreover, the height of the stunner compared to the size of the bird should be frequently monitored and adjusted. Only the head and neck should be submerged. The water should not reach the breast. The shackle guide bar must stay in contact with the shackle to close the electrical circuit, too.
Stun duration depends on the voltage level. In low voltage stunning, the birds should remain in the bath for 10 to 12 seconds. When higher voltages are used, less time is required.
Once the bird exits the stunner, stunning effectiveness should be closely monitored. Properly stunned birds will exhibit relaxed posture, straight – or only slightly curved – necks and minimal muscle spasms. The presences of an arched head, rhythmic breathing or wing flapping are indicators of insufficient stunning.
Slaughter
The automated neck cutter and guide bars should be adjusted to the right height and settings based on the bird’s size in order to position the head properly for the intended cut. The blade must be sharpened or replaced at appropriate intervals to maintain a clean cut.
Backup personnel should be present to ensure every bird receives a proper cut. A proper cut is assessed by the amount of blood flowing from the carcass or by the absence of the head. Any improperly cut or missed birds should be immediately cut by the backup personnel. Any deviation from proper shackling and well managed stunning and bleeding should be addressed immediately.
Controlled atmosphere stunning
There are currently two main types of CAS systems commercially available: carbon dioxide (CO2) stunning and low atmospheric pressure stunning (LAPS).
CO2 stunning works by increasing levels of the gas, and removing oxygen from the air, to cause hypoxia and death. LAPS works by decreasing the atmospheric pressure, and therefore decreasing available oxygen, causing hypoxia and death. Both methods render the bird unconscious prior to shackling and cause the irreversible loss of consciousness.
CAS best practices
In this set up, following lairage birds enter the plant and then enter the stunner while still in the transport module. Prior to entry into the system, the modules are monitored for the presence of birds unsuitable for slaughter. In systems where the birds are stunned within the transport module, removal of DOA occurs following stunning based on the presence of rigor.
Keeping this area at low light levels and a comfortable temperature will help keep the birds calm as they enter the controlled atmosphere stunning system. Calm birds are less likely to flap their wings, which can lead to wing damage.
When the birds enter a CAS system, unconsciousness is not instant. There is a period, lasting about a minute, where birds show some degree of head shaking, gasping and neck stretching. Birds shouldn’t show severe wing flapping or conscious attempts to escape the system. If severe behaviors are present, adjust the level of CO2 or the pressure.
Following unconsciousness, CO2 concentrations are increased, or pressure is decreased, depending on the system. Birds may undergo convulsions during this period. Indicators of severe convulsions is seen post-stun in the presence of broken wings, broken bones, and birds flipped to a breast-up/back-down position. If convulsions are too severe, adjustments can be made to decrease this symptom.
When leaving the system, the birds should be irreversibly stunned. Any recoveries should be noted immediately, and adjustments should be made to either increase the length of stunning following the loss of consciousness or to change stunning parameters.
Other factors to consider with CAS stunning
Temperature and humidity should also be considered in CAS systems. Both factors impact how birds react to the stun. Adjustments to stunning parameters must be made depending on whether the birds are coming in hot, exhibited by panting, or cold, exhibited by breathing more slowly. The precise adjustments needed based on these factors has yet to be scientifically determined. Typically, they are based on visualization of bird behavior and operator experience.
Finally, minimize the amount of time between stun and slaughter. In broilers, within 15 minutes rigor can become physically noticeable. Stiff carcasses will not pick properly and have a larger number of broken bones due to the lack of flexibility.
