Dr Marc Cooper, from the RSPCA's farm animal science department was flown to Toronto to speak about the use of carbon dioxide controlled atmosphere systems for killing meat chickens at a seminar organised by Dutch firm Meyn.

Dr Cooper, who is responsible for the development of the RSPCA welfare standards for both meat chickens and ducks, was invited to speak because of his wide-ranging and detailed research into gas killing systems which has seen him travel across the UK and to France, Germany and Austria.

He said: "I was very honoured to be invited to speak. The welfare of farm animals at slaughter is a very important issue and, when it comes to the use of gas, there are some important areas that need to be considered to ensure the process is conducted in the most humane way possible.

“At the moment, only one poultry processor in Canada uses a gas killing system. The majority of birds are slaughtered using conventional water bath stunning systems - which is essentially the opposite to the situation in the UK where most birds are killed using gas systems.

"This therefore presented a good opportunity to provide the Canadian industry with information to help them select the the right gas killing systems from a welfare point of view.”

The presentation focussed on the key areas that need to be considered to help achieve the most humane kill possible when using carbon dioxide gas killing systems.

There were about 90 representatives from all the major poultry processors in Canada in attendance, as well as Canadian government officials.

Dr Cooper added: "Even if just one processor takes our recommendations on board it could have a significant impact on the welfare of millions of birds."

Since his return from the conference Dr Cooper has been contacted by a number of processors asking for more information about the most humane gas killing systems.

From January next year (2016), except under very specific circumstances, abattoirs approved under the RSPCA Assured scheme, previously called Freedom Food, for processing spent hens, meat chickens and turkeys will no longer be able to shackle live birds. This means they will be required to use alternative systems to water bath stunning, such as gas killing systems.

The change in the standards has been introduced after extensive research showed that alternative killing methods, such as gas systems, can have major welfare benefits over the traditional shackling and water bath stunning methods.

Dr Cooper added: "It may seem strange for an animal welfare charity to be talking about killing animals but our welfare standards span the whole of the animal’s life - from birth (or hatching) to slaughter. A lot of discussions tend to focus on the rearing of animals, but we have to be concerned about the end of life too. It's very significant in terms of welfare."