McDonald's and Tyson Foods both severed ties with a Tennessee farm on 27 August, after an undercover video shot by animal rights activists was released that shows purported farm employees stabbing, clubbing and stomping on chickens. The video, which was unveiled by Mercy For Animals at a news conference in Los Angeles, depicts gruesome animal cruelty at what the group said was T&S Farm in Dukedom, Tennessee, which was under contract to Tyson Foods.

Tyson supplies chicken meat to McDonald's, the world's biggest fast-food chain, for its McNuggets. Representatives for T&S Farm could not immediately be reached for comment. "We are currently investigating this matter but based upon what we know, we are terminating the contract with the grower," said Christine Daugherty, the vice president of sustainable food production for Tyson Foods.

McDonald's said in a statement that it supported Tyson's decision and that it was working with the company to investigate the situation further. "We believe treating animals with care and respect is an integral part of a responsible supply chain and find the behaviour depicted in this video to be completely unacceptable," McDonald's said.

On the video, which Mercy For Animals activists said documented three weeks of animal abuse at the farm, workers can be seen stepping on birds' necks, stuffing them in cramped cages and bludgeoning them with clubs.

"Remember that for five years in a row, Tyson awarded grower of the year to this facility. So it's too little, too late," Mercy for Animals president Nathan Runkle told the news conference. He said the farm typically housed more than 120,000 chickens. "As a civilised society it is our moral obligation to prevent the suffering of all animals, including those that are raised and killed for food."

McDonald's announced earlier this year it would phase out its use of chickens raised with certain kinds of antibiotics at its 14,000 US restaurants as part of a restructuring plan to reverse a long sales slump.