Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 4, 2007
Publication Date: August 25, 2007
Citation: Purswell, J.L., Thaxton, J.P., Branton, S.L. 2007. Identifying Process Variables for a Low Atmospheric Pressure Stun/Kill System. Journal of Applied Poultry Research. 16:509-513. Interpretive Summary: Gas stunning of poultry is being considered as an alternative to traditional waterbath stunning prior to slaughter of the approximate 8.3 billion chickens processed annually by the poultry industry. Gas stunning systems typically use carbon dioxide, argon, or a mixture of these gases to reduce oxygen levels. However, limitations arise from maintaining proper concentrations of gases in these systems. Reducing atmospheric pressure is being investigated as an alternative means of reducing oxygen levels. Because pressure is uniformly exerted, problems with maintaining proper concentrations of stunning gases do not occur. A series of experiments showed that reduced air pressure produces similar rates of effectiveness and process time results as compared to gas-based processes. A low atmospheric pressure system (LAPS) may provide economic and safety advantages over gas based systems. The LAPS process uses atmospheric air, eliminating the need for purchase or on-site generation of process gases. Safety concerns regarding worker exposure to process gases are eliminated, and any leaks would allow air into the system, rather than discharging it.
Technical Abstract: Current systems for pre-slaughter gas stunning/killing of broilers use process gases such as carbon dioxide, argon, or a mixture of these gases with air or oxygen. Both carbon dioxide and argon work by displacing oxygen to induce hypoxia in the bird, leading to unconsciousness and ultimately death. In this study, mechanical removal of oxygen by reducing air pressure was investigated as an alternative to carbon dioxide or argon based stun systems. Low atmospheric pressure systems could offer advantages in worker safety and operational cost because they operate solely with air. This study was comprised of two experiments, one to define the initial range of effective pressures, and the second to determine a recommended process pressure. In Experiment 1, 48 female broilers aged 56 d were subjected to 6 different pressure treatments ranging from 70.9 to 30.4 kPa. In Experiment 2, 56 male broilers aged 60 d were subjected to 7 different pressure treatments ranging from 35.5 to 20.3 kPa. Birds were individually placed in a air-tight vessel and exposed for two minutes after final pressure was attained. Results from Experiment 1 showed that the effective range of pressure was between 30.4 and 20.3 kPa, with only 25% of the birds exposed to 30.4 kPa surviving and none of the birds exposed to 20.3 kPa surviving. Experiment 2 used finer resolution in pressure increments and an estimated pressure level lethal for 99% of birds was determined to be 24.1 kPa.