Written by Mudra Pal

Electrical stunning methods result in severe welfare problems for billions of birds each year. On the other hand, the controlled-atmosphere killing of birds in their transport containers (prior to shackling) has proved to be both far more humane and less likely to cause carcass degradation. Under the most humane controlled-atmosphere killing model, birds are taken directly from the transport vehicles in their crates or modules, which are inserted into a chamber where controlled-atmosphere killing occurs. The dead animals are then shackled, cut, bled, scalded, and eviscerated. At no point during this process can the animals experience pain or suffering. The switch from electrical stunning to controlled-atmosphere killing would result in such vast welfare improvements that according to one of the world’s foremost experts on the subject (Raj 1998b), doing so would eliminate the “stress and trauma associated with removing conscious birds from their transport containers, in particular, under the bird handling systems which require tipping or dumping of live poultry on conveyors; the inevitable stress, pain and trauma associated with shackling the conscious birds, i.e., compression of birds’ hock bones by metal shackles; the stress and pain associated with conveying conscious birds hanging upside down on a shackle line which is a physiologically abnormal posture for birds; the pain experienced by some conscious birds that receive an electric shock before being stunned (pre-stun shocks); the pain and distress experienced by some conscious birds which miss being stunned adequately (due to wing flapping at the entrance to the water bath stunners) and then pass through the neck cutting procedure; [and] the pain and distress associated with the recovery of consciousness during bleeding due to inadequate stunning and/or inappropriate neck cutting procedure.”

While the costing associated with CAS installation is more than electrical stunning. Some data indicates improved product quality over electrical stunning. Suggestions exist that meat quality may be improved in the form of fewer broken wings; fewer breast fillet haemorrhages, and less leg damage. However, conflicting information also shows that wing damage is higher in CAS systems. Variations in controlled atmosphere stunning system type and gas used can also affect end-product meat quality. While CAS was estimated to have a higher cost, there may potentially be increased revenue. CAS would allow access to certain markets based on customer requirements for specific animal welfare practices.

Stunning is a step that renders animals insensible to pain before processing. Most poultry plants use electricity, a method introduced in the 1960s. By contrast, CAS, which has been widely adopted in Europe and supported by leading animal welfare organizations, changes the concentrations of gas in the air the chickens breathe to bring about a loss of consciousness. Perdue Farms this year switched completely to CAS. In a typical poultry plant, employees pick up live birds to shackle them upside down while they’re still conscious. With its CAS system, Perdue uses increasing levels of carbon dioxide to calm, then sedate the chickens, before bringing about an irreversible loss of consciousness prior to processing. Since birds are stunned before handling, no bird is upside-down while conscience for any period of time. This, according to Perdue, improves poultry welfare – and creates a better working environment for employees.

Overall benefits of CAS-

  • Improved Carcass and Meat Quality
  • Fewer broken bones, less haemorrhaging, and reduced bruising:
  • Reduced internal and external contamination:
  • Improved shelf life and quality
  • Unimpeded bleed-out rate
  • Increased Revenue
  • Increased meat yield
  • Reduced refrigeration and energy costs:
  • Reduced labour costs
  • Improved worker conditions and safety:
  • Environmental benefit

In summary, it is clear that electrical stunning methods used in the U.S. do not lead to humane deaths for chickens. During this process, chickens endure the stress and pain of being dumped onto a crowded conveyer, where they sometimes suffocate; being hung upside-down by their legs in shackles and sometimes being ripped from the shackles when they are improperly hung; and experiencing painful pre-stun shocks from the stun bath. Most birds are immobilized from the stun bath but fully conscious when they have their necks cut, and many are scalded alive.


Controlled-atmosphere killing methods using mixtures of inert gases, preferably 80 percent nitrogen and 20 percent argon, help significantly alleviate these welfare problems and, at the same time, improve carcass quality and revenue for the producer. The initial costs for a complete controlled-atmosphere killing line can be recovered quickly— within 3.5 to 4.5 years based on improvements in meat yield alone and much faster as other benefits are realized. After payback, producers will experience even greater savings and will continue to profit at an accelerated rate as a result of the switch.







Written by

Mudra Pal

She is currently pursuing Bachelors in Food Technology from Jamia Hamdard, Delhi INDIA. 

LinkedIn: https://www.linkedin.com/in/mudra-pal-9a3258129/


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