The method, known as “Ventilation Shut Down”, sparked criticism last week when the US Department of Agriculture released its new control strategy for containing highly pathogenic avian influenza (HPAI).

Heat of between 100 and 120 degrees Fahrenheit is maintained for seven days with at least three days being consecutive.

The technique is to be used when other methods laid out in Fall 2015 HPAI Preparedness and Response Plan look incapable of exterminating the virus inside the 24 hour cull period after diagnosis.

The debate comes ahead of a seasonal increase in bird flu risk as bird migrate south from Canada ahead of winter.

No special equipment or personnel are required. Justifying the method, the USDA said: “While not a preferred method, it could save the lives of thousands of birds by reducing the risk of disease spread.”

The Humane Society (HSUS) described it as the “inhumane mass baking of live chickens”.

Standard methods, described by the USDA as “foaming, C02” are “preferred” as they most human and effective way to depopulate large poultry flocks, said the USDA plan.

In his criticism, HSUS chief veterinary officer Michael Blackwell called for research and testing of more humane methods.

Mr Blackwell said the industry and USDA need to find a better way to contain the spread of bird flu.

He added: “Animals suffer immensely with any outbreak of an epidemic like avian influenza, and we shouldn’t compound the problems for birds by subjecting them to a particularly miserable and protracted means of euthanasia.”

Earlier, the National Chicken Council stressed “rigorous implementation” of biosecurity principles would be essential.

Speaking ahead of the winter bird migration last month, NCC President Mike Brown said: “I know each industry has been preparing similarly. By maintaining this strong collaboration and sharing of lessons learned, I am confident we will all be in a much better place this year.”

Poultry business hit by the virus are to be compensated 100 per cent of “fair market value” for birds lost.

The HSUS also claims confined systems are more susceptible to bird flu, calling on the government to assist in the cage to cage-free transition.

Over 48 million chickens were destroyed in the US HPAI outbteak this spring - the worst animal disease outbreak in US history, according to the USDA.

Confirmed in 21 states, the outbreak ended with the last confirmation on June 17.