By Jonathan Tolliver and Dan Whitcomb LOS ANGELES (Reuters) - McDonald's Corp and Tyson Foods both severed ties on Thursday with a Tennessee farm where workers were seen stabbing, clubbing and stomping on chickens in an undercover video shot by animal rights activists. The videotape, which was unveiled by Mercy For Animals at a news conference in Los Angeles, depicts gruesome animal cruelty toward the birds at what the group said was T&S Farm in Dukedom, Tennessee, which was under contract to Tyson Foods (TSN.N). Tyson supplies chicken to McDonald's (MCD.N), the world's biggest fast-food chain, for its McNuggets. Representatives for T&S Farm could not be reached for comment. "Animal well-being is a priority at our company and we will not tolerate the unacceptable animal treatment shown in this video,"... More