The Humane Society of the United States (HSUS) conducted the investigation at Butterfield Foods, has released video and other results of the investigation and reported possible illegal activity to authorities following an undercover exposé at a “spent” egg-laying hen slaughter plant in Butterfield, Minnesota, revealed inhumane treatment of animals and potentially illegal cruelty.

HSUS says this is the first undercover investigation of a spent hen slaughter plant in the country.

The Society describes spent hens as 'egg-laying birds who are no longer commercially profitable, and are used for cheap meat after their lifelong confinement producing eggs in “battery cages” ends'.

HSUS made the following allegations:

• Many birds each day were scalded alive
• Hens arrived in trucks packed so tightly they could barely move.
• Hens were removed from crates and shackled upside down while alive and fully conscious.
• Birds were ineffectively stunned and inhumanely killed.
• Sick and injured birds were thrown against the wall or tossed in the trash.

Paul Shapiro, HSUS vice president of farm animal protection, commented: “Egg-laying hens suffer tremendously, locked in cramped cages their whole lives only to then be inhumanely slaughtered when their productivity wanes. Consumers can help reduce the suffering of animals in factory farms by eating less chicken, and the US Department of Agriculture can help poultry by requiring slaughter plants to switch to higher-welfare systems such as controlled atmosphere killing.”

The HSUS allegations are made against Butterfield Foods, which is owned by Mankato-based Downs Food Group.

Responding to the allegations, an attorney representing Butterfield, Terry Fruth, told Star Tribune that the company adheres to standards for humane slaughter, and that on-site company and government observers ensure that.

He said: “There are industry guidelines, and we are in compliance with all of them. There are government rules, and we follow them.”

Chickens in the United States are usually slaughtered by being shackled upside down, then stunned in an electrified water bath before having their throats cut, according to Star Tribune. The birds bleed out and are then deposited into a vat of scalding water to loosen feathers for plucking.

Butterfield says the allegation that its slaughter process allowed an inordinate number of birds to hit the scalding pot alive and conscious is incorrect.

In addition, HSUS says it has information to support the claim that some major egg producers in Minnesota do not even meet the voluntary space allotment standard established by the United Egg Producers, the national trade association of the egg industry. That voluntary standard, widely considered to be inhumane because it immobilises birds, may cover about 75 per cent of laying hens in cage confinement. Some major producers in Minnesota keep hens in 48- or 54-inch space allotments, which amounts to extraordinary deprivation and suffering for the birds.

Wayne Pacelle, president and CEO of HSUS, added: “Laying hens in Minnesota are suffering from birth to death, and every step of the process is filled with misery for so many millions of these birds.”

In a blog dated 5 January, Mr Pacelle wrote: "California’s Prop 2 took effect on New Year’s Day, and we’ve been urging major food retailers to honour the letter and spirit of the law by not buying or selling any animal products that come from caged farm animals, with a particular focus on laying hens in cages.

"While continuing to advance the argument that cage-free production should be the minimum standard in California, and eventually the nation, The HSUS is also today shining a spotlight on the lives and deaths of laying hens in the Midwest. Specifically, after reviewing the report and footage from one of our brave undercover investigators who worked at Butterfield Foods Co. - a slaughter plant in Minnesota - I say, without hesitation, that laying hens are some of the most abused animals on the planet. They face abject misery and privation throughout their lives and then terror and inhumane treatment during transport and slaughter."