Chicken Gassing in the UK
Summary — Quick overview
SUMMARY
Over 1.1 billion chickens are slaughtered in the UK each year, more than three million every day, making them by far the most slaughtered land animals in the country. Most meat chickens are fast-growing broilers killed at just six to seven weeks old, despite a natural lifespan of 12 years or more. Around 25 million egg-laying hens are also slaughtered annually when they are considered no longer profitable, and an estimated 40 to 45 million male chicks are killed soon after hatching because they are of no use to the egg industry.
By law, chickens are supposed to be stunned before slaughter, and gas stunning is now the most common method in the UK. About 77 per cent of chickens raised for meat, and nearly all older laying hens, are stunned this way. Systems use carbon dioxide, inert gases such as argon or nitrogen, or mixtures of these gases to reduce oxygen until birds lose consciousness and die. In many modern systems, chickens remain in transport drawers while moving through tunnels with rising gas concentrations.
These methods raise serious welfare concerns. Chickens can detect carbon dioxide at very low levels, and higher concentrations can cause gasping, head shaking, shrieking, jumping and attempts to escape before they lose consciousness. Carbon dioxide stunning is not immediate: at around 40 per cent CO₂, unconsciousness usually takes about a minute, while phased systems can take up to four minutes. Many welfare groups want all CO₂ systems for poultry to be phased out, and the clearest way to end this suffering is to stop eating chickens.
KEY FACTS
- More than 1.1 billion chickens are slaughtered in the UK every year, which is over three million a day.
- Most chickens raised for meat are broilers bred to grow quickly and are usually killed at only six to seven weeks old.
- About 25 million egg-laying hens are slaughtered annually in the UK when they are considered ‘spent’ and no longer profitable.
- An estimated 40 to 45 million male chicks are killed each year soon after hatching because they cannot lay eggs and are not bred for meat.
- Gas stunning is the main slaughter method for UK chickens, used for about 77 per cent of birds raised for meat and nearly all older laying hens.
- Approved gas systems use carbon dioxide, inert gases such as argon or nitrogen, or combinations of these gases to reduce oxygen until birds lose consciousness and die.
- Most poultry gas stunning in the UK uses phased CO₂ systems, accounting for 58 per cent of birds, while another 19 per cent are stunned using other gas mixtures.
- Chickens can experience pain, fear and distress during CO₂ exposure, showing reactions such as gasping, head shaking, shrieking, jumping and attempts to escape before losing consciousness.
FAQ
How are most chickens killed in the UK?
Most are killed by gas stunning. According to the Food Standards Agency, about 77 per cent of chickens raised for meat are stunned using gas, and nearly all older egg-laying hens are killed this way. The gases used include carbon dioxide, argon, nitrogen or mixtures of them.
Why is chicken gassing a welfare concern?
Carbon dioxide can cause serious distress before birds lose consciousness. Chickens can detect CO₂ at very low levels, and as concentrations rise they may gasp, shake their heads, shriek, jump and try to escape. Unconsciousness is not immediate, so birds can suffer pain and fear during exposure.
How long does it take for chickens to lose consciousness when gassed?
It is not instantaneous. Chickens exposed to about 40 per cent CO₂ usually lose consciousness after around one minute. In phased systems, where concentrations rise gradually, it can take up to four minutes.
Chickens are the most commonly slaughtered farmed animals in the UK.
Chickens are by far the most commonly slaughtered farmed animals in the UK, with over 1.1 billion killed every year – more than three million every day, far exceeding pigs, sheep, cattle, ducks and turkeys combined.
Most are killed by exposure to carbon dioxide (CO₂), despite the fact that chickens are highly sensitive to this gas, detecting it even at very low concentrations. As CO₂ levels rise, they show clear signs of pain and distress, including gasping, vigorous headshaking and escalating panic behaviours such as struggling, vocalising and attempting to escape before losing consciousness and dying.
How chickens are bred and raised
Broilers
Most chickens raised for meat in the UK are broiler breeds selected to grow very quickly. They are usually slaughtered at around just six to seven weeks old. A chicken’s natural lifespan could be 12 years or more. Over one billion broilers are slaughtered for food in the UK every year.1Defra. 2025. Agriculture in the United Kingdom 2024. Available at: Agriculture in the United Kingdom 2024 – GOV.UK
Egg-layers
Egg-laying chickens used on farms are usually killed when they are about 18 months old. By that age, they lay fewer eggs, so farmers often consider them ‘spent’ – no longer profitable to keep. In the UK, about 25 million of these hens are slaughtered every year.2Food Standards Agency (FSA). 2025. Freedom of Information request Viva! FOI 00033, January 17, 2025. Their meat is tougher than the meat from chickens raised specifically for eating (called broilers), so it is rarely sold as regular chicken. Instead, it is often processed into low-cost food ingredients, exported frozen or used in pet food.
Chicks
Chicks are of no use to the egg industry because they cannot lay eggs and they are not bred to grow enough for meat. Because of this, they are usually killed soon after they hatch. Each year, an estimated 40 to 45 million male chicks are killed. Their bodies are often used as food for pets and zoo animals, especially reptiles and birds of prey.3Animal Welfare Committee (AWC). 2023. Opinion on alternatives to culling newly hatched chicks in the egg and poultry industries. Available at: Animal Welfare Committee: opinion on alternatives to culling newly hatched chicks in the egg and poultry industry.
Stunning and Slaughter
By law, chickens must be stunned before slaughter, so they lose consciousness first (although there are exceptions for some religious slaughter methods – see here).
In the UK, the two main stunning methods are:
- Gas stunning: chickens are exposed to gases such as CO₂ or inert gases such as argon or nitrogen, which make them lose consciousness and then results in death due to the lack of oxygen
- Electrical water-bath stunning: chickens are placed on a conveyor line and their heads pass through electrified water that stuns them. After this their throats will be cut and the birds will bleed out and die from blood loss
According to the Food Standards Agency, gas stunning is now the most common method. About 77 per cent of chickens raised for meat and nearly all older egg-laying hens are stunned this way.4Food Standards Agency (FSA). 2024. Results of the 2024 FSA Slaughter Sector Survey in England and Wales. Available at: https://www.gov.uk/government/publications/farm-animals-slaughter-sector-survey-2024
Male chicks that are killed shortly after hatching are usually killed in a different way, using a chamber filled with the inert gas argon, which removes oxygen and causes them to lose consciousness and die.3Animal Welfare Committee (AWC). 2023. Opinion on alternatives to culling newly hatched chicks in the egg and poultry industries. Available at: Animal Welfare Committee: opinion on alternatives to culling newly hatched chicks in the egg and poultry industry.
Methods used to stun and kill poultry
UK rules allow chickens to be stunned using gases, such as carbon dioxide or inert gases, which first render them unconscious and then kill them. These are set out in the Welfare of Animals (Slaughter or Killing) Regulations 1995 and later updates.5Defra. 1995. Welfare of Animals (Slaughter or Killing) Regulations 1995. SI 1995 No 731. Available at: https://www.legislation.gov.uk/uksi/1995/731/contents In simple terms, the approved methods are:
- High-concentration carbon dioxide (CO₂)
Birds are placed in a chamber with a high level of CO₂ gas (at least 40 per cent). The gas removes oxygen, causing the birds to lose consciousness and die. This method raises many welfare concerns because birds experience pain and distress when first exposed to high levels of CO₂. - CO₂ stunning in phases
This method introduces CO₂ gradually, first exposing birds to a lower level of CO₂ so they become unconscious and then to a higher level to ensure death. Many modern slaughter systems use this staged approach in an effort to reduce the distress caused by immediate exposure to high CO₂ levels. - CO₂ mixed with other gases
CO₂ can be combined with gases such as nitrogen or argon to lower oxygen levels, which causes birds to lose consciousness. The aim is to reduce some of the discomfort associated with CO₂ alone. - Inert gases only (argon or nitrogen)
Some systems use gases such as argon or nitrogen without CO₂. These gases lower oxygen levels, causing unconsciousness. This approach is less common for meat chickens but is widely used in the UK for killing newly hatched chicks.
In summary, all these methods use gases that reduce oxygen, causing birds to first lose consciousness and then die from the lack of oxygen.
Source: Defra, 1995.
The Stages of a Gas Chamber
Gas Chamber. Chickens are put in transport drawers and moved through increasing concentrations of CO₂.
In many modern gas stunning systems, chickens stay in transport drawers as they move along a conveyor through a tunnel filled with CO₂. The tunnel is divided into several sections, where the gas levels increase. Chickens first enter areas with lower CO₂ levels and then move into sections with much higher levels. This is designed to make them lose consciousness and then die. Designs vary depending on the manufacturer – in some systems, birds stay in drawers the whole time, while in others they may be unloaded onto a conveyor belt.
UK poultry gas stunning breakdown
Around 77 per cent of poultry in the UK are stunned using gas and most of those (58 per cent) are stunned using CO₂ in phases, while the remaining 19 per cent are stunned using other gas mixtures, likely containing CO₂, nitrogen and argon.4Food Standards Agency (FSA). 2024. Results of the 2024 FSA Slaughter Sector Survey in England and Wales. Available at: https://www.gov.uk/government/publications/farm-animals-slaughter-sector-survey-2024
Pain, fear and distress
Chickens can sense CO₂ at very low levels – even below five per cent – and may stop eating when exposed. At 15 per cent, CO₂ can cause birds to gasp and shake their heads.6European Food Safety Authority (EFSA). 2004. Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals. EFSA Journal. 45, 1-29. Available at: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2004.45 As levels rise from six to 30 per cent, they show stronger signs of distress – shrieking, jumping and attempting to escape – until they lose consciousness.7Mace JL and Knight A. 2026. To what extent do chickens suffer when gassed with CO2? Frontiers in Veterinary Science. 12, 1719226. Similar reactions in pigs have led many experts to criticise using CO₂ for stunning.
See more on pig gassing.
CO2 stunning is not instantaneous
CO₂ stunning doesn’t work instantly. Chickens exposed to about 40 per cent CO₂ usually lose consciousness after around one minute, while using a gradual, phased approach can take up to four minutes. It’s still unclear whether short, intense pain and distress is worse or better for the birds than longer, milder pain and distress.7Mace JL and Knight A. 2026. To what extent do chickens suffer when gassed with CO2? Frontiers in Veterinary Science. 12, 1719226. The best choice would be to just stop eating chickens!
Over the past 20 years there have been repeated calls from scientific and advisory bodies for the phasing out of CO₂ stunning in pigs.8European Food Safety Authority (EFSA). 2020. Welfare of pigs at slaughter. EFSA Journal. 18 (6) 6148. Available at: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2020.61489Animal Welfare Committee (AWC). 2025. Opinion on the welfare impacts on pigs of high concentration CO2 gas stunning and of potential alternative stunning methods. Available at: https://www.gov.uk/government/publications/opinion-on-carbon-dioxide-gas-stunning-of-pigs-and-alternative-methods Many welfare groups would like to see this extended to include all CO₂ systems used to stun poultry.
We must act now on chicken gassing. Find out what you can do to help end this cruel practice once and for all.
References
- Animal Welfare Committee (AWC). 2025. Opinion on the welfare impacts on pigs of high concentration CO2 gas stunning and of potential alternative stunning methods. Available at: https://www.gov.uk/government/publications/opinion-on-carbon-dioxide-gas-stunning-of-pigs-and-alternative-methods
- Defra. 2025. Agriculture in the United Kingdom 2024. Available at: Agriculture in the United Kingdom 2024 – GOV.UK
- Food Standards Agency (FSA). 2025. Freedom of Information request Viva! FOI 00033, January 17, 2025.
- Animal Welfare Committee (AWC). 2023. Opinion on alternatives to culling newly hatched chicks in the egg and poultry industries. Available at: Animal Welfare Committee: opinion on alternatives to culling newly hatched chicks in the egg and poultry industry.
- Food Standards Agency (FSA). 2024. Results of the 2024 FSA Slaughter Sector Survey in England and Wales. Available at: https://www.gov.uk/government/publications/farm-animals-slaughter-sector-survey-2024
- Defra. 1995. Welfare of Animals (Slaughter or Killing) Regulations 1995. SI 1995 No 731. Available at: https://www.legislation.gov.uk/uksi/1995/731/contents
- European Food Safety Authority (EFSA). 2004. Opinion of the Scientific Panel on Animal Health and Welfare on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals. EFSA Journal. 45, 1-29. Available at: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2004.45
- Mace JL and Knight A. 2026. To what extent do chickens suffer when gassed with CO2? Frontiers in Veterinary Science. 12, 1719226.
- European Food Safety Authority (EFSA). 2020. Welfare of pigs at slaughter. EFSA Journal. 18 (6) 6148. Available at: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2020.6148
