Supermarket chain Asda has sparked a fresh row over poultry farming by instructing slaughterhouses to gas chickens and turkeys to death.
Animal welfare groups have voiced concerns over the effect of some of the gases used, while rival supermarkets have expressed fears over the possible effects of the gas on meat quality.
Under the method, called controlled atmosphere killing (CAK), the supermarket's suppliers will load chickens into crates, which will be passed through a multi-stage machine in which oxygen levels are reduced, leaving the birds to breathe only carbon dioxide until they are dead.
David Mainon, senior technical manager at Asda, said: "This method means that birds are only handled once whilst alive, and the birds are settled on the farm and so are less stressed".
"We have encouraged all our poultry suppliers which do not currently have controlled atmosphere killing to instigate plans to convert their current system of stunning, to this method" said Mr Mainon.
More than 800 million chickens are slaughtered in the UK every year, 75 per cent of which are hung upside down, shackled and electrically stunned before being decapitated. This has been widely condemned by animal welfare groups as unsatisfactory, due to the pain and distress caused by shackling and stunning the chickens.
Compassion in World Farming said scrapping the electrocution and decapitation were steps towards more humane slaughter, but expressed concern over the gassing of the birds. "From a welfare point of view, it would be better if carbon dioxide wasn't used" said Peter Stevenson, chief policy advisor at Compassion in World Farming. "Carbon dioxide causes the birds respiratory distress – hyperventilation and gasping" said Mr Stevenson. "The reason slaughterhouses want to use it is because the alternative -high levels of nitrogen or argon - can cause reflex wing flapping. The birds are unconscious, but they flap their wings and that can cause damage to the carcass" said Mr Stevenson.
And a spokesman for Waitrose said: "There is currently conflicting information regarding the anoxic convulsions the birds suffer during killing under the CAK system and whether this results in suffering for the birds. As a result we have decided not to use this method of slaughter at the present time".
Despite this, it is thought that Asda's decision may encourage other major retailers to switch to CAK, with Tesco, Sainsbury's, Somerfield and The Co-operative all holding talks on the subject in recent weeks.
And more than one leading supermarket voiced fears that there was not enough evidence to prove that controlled atmosphere killing did not affect meat quality.
CAK was first approved for use in the UK in 1995. Since then it has been much more popular elsewhere in Europe.
It has backing from the animal welfare group PETA. "CAK eliminates all handling with live birds at slaughter, the need for shackling birds while they are alive, and the electric stun tank entirely," said Matt Prescott of PETA. "Those poultry producers that have switched to it have been documented as saying that it has improved animal welfare, human safety and even output at their facilities" said Mr Prescott.
But Andrew Tyler, Director of Animal Aid, said: "It is hard to regulate gassing animals, and there is an element of 'problem solved' here when it is not. Issues of cost-cutting, incompetence and callousness – and there has been a lot of evidence of the things these birds are subjected to in slaughterhouses – are still there. There has to be proper regulation and enforcement put in place to make sure that these things don't take place."Reuse content