(Mike Blake/Reuters)

Chickens used to make McDonald's McNuggets were beaten with a nail attached to a pole, tossed alive into buckets meant for the dead and suffered from leg deformities at a farm under contract with Tyson Foods, according to an animal rights  group.

Tyson Foods quickly cut its ties with the Tennessee farm after a video showing the alleged abuse was released Thursday by Mercy for Animals, a nonprofit based in Los Angeles that employs workers to infiltrate farms and record animal mistreatment.

The video shows "birds painfully beaten, stabbed, and impaled on makeshift clubs" at T&S Farms in Dukedom, Tenn., a statement by the group said.

This video from Mercy for Animals shows "birds painfully beaten, stabbed, and impaled on makeshift clubs" at T&S Farms in Dukedom, Tenn. (Mercy for Animals)

Footage also shows factory "farm owners stepping on the heads of live chickens and then pulling their wings or bodies to break their necks, chickens bred to grow so fast they became crippled under their own weight and frequently died from organ failure, hundreds of thousands of birds crammed into filthy, windowless sheds forced to live for weeks in their own waste."

[Your pig almost certainly came from a factory farm, no matter what anyone tells you]

What Mercy for Animals called an investigation started July 28 and ended last Sunday, said Matt Rice, a spokesman for the group. The activist applied for a job and used a hidden camera to show workers spiking chickens, then saying, "You didn't see that." The footage was turned over to local police, Rice said. The activist who shot the video was not named.

The owners of the farm, Thomas and Susan Blassingame, did not return a voice mail message asking for comment. Tyson Foods issued a statement Thursday saying the company has launched its own investigation, but "based on what we currently know, we are terminating the farmer's contract to grow chickens for us." Tyson said an estimated 125,000 birds have been removed from the farm's barns.

"We're especially concerned about the inappropriate methods used to euthanize sick and injured chickens," Tyson said in a statement supplied by spokesman Gary Mickelson. "We're committed to animal well-being but don’t believe this video accurately depicts the treatment of chickens by the thousands of farmers who supply us."

Although the farm was in the Tyson supply chain, Mercy for Animals blamed the mistreatment on the global restaurant chain McDonald's.

"McDonald’s is one of the largest fast-food chains in the world and a top customer to Tyson Foods," the rights group said. It called on McDonald’s to "adopt meaningful animal welfare policies to end many of the worst forms of animal abuse and neglect in its supply chain."

McDonald's said in a statement that it finds the "behavior depicted in this video to be completely unacceptable" and supported Tyson's move to cut off the farm. The statement went on to say that the restaurant is "working with Tyson Foods ... to further investigate this situation and reinforce our expectations around animal health," but wasn't specific about how that is being done.

[Why it's huge news that Wal-Mart is pushing stricter animal welfare policy]

"This is sickening animal abuse no company with morals should support," said Nathan Runkle, president of Mercy for Animals. "McDonald’s has not only the power but also the ethical responsibility to end the worst forms of cruelty to animals in its supply chain.”

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