The proposals are part of amendments to the The Welfare of Animals (Slaughter or Killing) Regulations 1995 (WASK), which have been sent out for consultation in the industry by the Department of Environment Food and Rural Affairs (Defra).

The amendments also include provisions to extend the range of birds that may be killed on-farm by gas mixtures and extend the time limit for bringing a prosecution under WASK.

The changes to the legislation and the consultation only apply to the industry in England.

Defra said that the proposal to amend WASK will be primarily of interest to poultry slaughterhouse operators, poultry and egg producers and animal welfare organisations.

The Welfare of Animals (Slaughter or Killing) Regulations 1995 (WASK) are part of an EC directive that establishes common minimum standards across the EU for the protection of animals at the time of slaughter or killing.

The new regulation that will come into force in 2013 will replace the directive and it is anticipated that new domestic regulations will be introduced to repeal the existing provisions in WASK and enforce the directly applicable obligations in the regulation.

At present, WASK sets out sets out the arrangements to protect the welfare of pigs and birds killed by exposure to gas mixtures in slaughterhouses.

It limits the use of gas mixtures to kill birds in a slaughterhouse to:

• Argon, nitrogen or other inert gases, or any mixture of those gases in atmospheric air with a maximum of two per cent oxygen by volume; or
• Any mixture of argon, nitrogen or other inert gases with atmospheric air and carbon dioxide providing the carbon dioxide volume does not exceed 30 per cent by volume and the oxygen concentration does not exceed two per cent by volume.

Regulation 1099/2009 permits the use of carbon dioxide in two phases to kill poultry, where this involves successive exposure to a gas mixture containing up to 40 per cent carbon dioxide followed, when animals have lost consciousness, by a higher concentration of carbon dioxide.

The amendment proposes to permit the use of biphasic carbon dioxide in slaughterhouses comprising a mixture of up to 40 per cent of carbon dioxide in atmospheric air (phase 1) followed by a mixture containing a minimum of 70 per cent carbon dioxide in atmospheric air (phase 2).

The original regulations in WASK were formed when it was considered that anoxic gas mixtures were more humane than hypercapnic hyperoxygenated gas mixtures followed by a second euthanasia phase.

The main reason for this was that there was evidence of aversion, indicated by withdrawal from the feeding area, seen at higher concentrations of carbon dioxide (40 per cent, 55 per cent and 70 per cent).

Later research has reported that hypercapnic hyperoxygenated gas mixtures (i.e. a gas mixture containing carbon dioxide and a relatively high level of oxygen that will cause excess levels of carbon dioxide in the blood) are linked to strong respiratory responses (i.e. gasping) but there is limited evidence of pain and aversiveness in birds at low to intermediate carbon dioxide concentrations (<30 to 40 per cent).

Further research has indicated that anoxic gas mixtures induce unconsciousness faster, however, they are linked to an early onset of stronger behavioural responses in the form of wing flapping before the bird reaches unconsciousness.

The onset of this response was earlier in anoxic gas mixtures than with the two-phase approach.

The most recent papers report that the smoother transition to unconsciousness produced by hypercapnic hyperoxygenated gas mixtures is preferred to the fast induction and convulsions associated with anoxic mixtures.

Literature reports that gas mixtures comprising 30 per cent carbon dioxide / 40 per cent oxygen / 30 per cent nitrogen and 40 per cent carbon dioxide / 30 per cent oxygen / 30 per cent nitrogen render birds unconscious within one minute.

This is followed by a killing gas mixture containing 80 per cent carbon dioxide and no more than two per cent oxygen in air or 80 per cent carbon dioxide / five per cent oxygen / 15 per cent nitrogen.

The amendment will allow this biphasic approach to be used in poultry slaughterhouses and is being discussed now so that business operators to make investment decisions and, in some cases, plant modifications before 1 January 2013.

Defra said that the use of gas-killing systems for poultry has a number of welfare and commercial advantages over conventional electrical water-bath stunning. These include:

• minimal pre-slaughter handling and no need for live shackling, reducing levels of suffering, pain, distress and potential risk of injury to the welfare of the animals
• improved health and safety of persons hanging birds on the shackle line hangers, who will hang dead rather than live birds
• birds are killed within their crates
• the possibility of pre-stun shocks is eliminated
• the possibility of birds receiving inadequate current levels or missing stunning altogether is eliminated, and
• the killing of birds using gas mixtures is associated with a lower incidence of broken bones and internal haemorrhaging compared to electrical water-bath stunning, which can improve carcass quality.

Defra added that the Impact Assessment shows that the use of biphasic carbon dioxide will reduce operating costs for slaughterhouse operators.

It is anticipated that the proposed changes to WASK will ease a switch to gas-killing and reduce use of water-bath stunning systems, which are generally acknowledged to provide a lower standard of welfare.

"Science has moved forward since the last changes to gas mixtures were made in 2001. The latest evidence indicates that hypercapnic hyperoxygenated gas mixtures, such as those used in biphasic carbon dioxide systems, are an at least as humane method of stunning poultry as anoxic gas mixtures," Defra said.

"These sources also confirm gas killing methods address some of the major concerns associated with other stunning methods."