mitigation strategies in the castration of piglets, and avoiding killing piglets through blunt force. Animal rights activities called on Tyson to make the guidelines a "mandate" rather than a "recommendation." In 2015, Tyson Foods severed ties with a supplier after Mercy For Animals published videos showing that employees at a Tyson supplier were stabbing, clubbing and stomping on chickens. A 2016 undercover investigation by the animal rights organization Compassion Over Killing showed workers at four separate Tyson processing plants throwing, punching and kicking chickens, as well as sticking plastic rods through their beaks. They also wrung birds' necks, ran over them with forklifts, and left injured birds in heaping piles to die. A 2017 investigation showed more abuse and cruelty towards chickens. After the 2017 investigation, Tyson responded by saying it would introduce a remote video auditing system to monitor treatment of chickens in its supply chain and hire off-site auditors. The company also started a pilot program for controlled atmosphere stunning, considered to be a more humane method of slaughter. Animal rights activists said the measure did not go far enough. In 2017, Matthew Prescott of the Humane Society of the United States criticized Tyson for failing to implement many of the animal welfare standards that other food suppliers were adopting. In 2020, Tyson worked with the University of Arkansas System Division of Agriculture to investigate the effects of lighting on broiler chicken welfare. Their research project, "Effect of Variable Light Intensity Program on Broiler Gait Score, Stress and Central Positive Welfare in Commercial Broiler Farm", received a $110,000 grant from the U.S. Poultry and Egg Association. Following a 2020 complaint, the Federal Trade Commission is investigating Tyson for making false and misleading advertising claims regarding the treatment of its chickens. Food recalls On January 30, 2019, Tyson Foods announced a recall for over 36,000 pounds of chicken nuggets that were at risk of being contaminated with small pieces of rubber. The recall followed allegations by consumers who submitted complaints to the U.S. Agriculture Department. Tyson identified the contaminated nuggets as those received by Arizona, California, Illinois, New Jersey, and Utah club store distribution centers. On March 21, 2019, the company issued a recall for 69,000 pounds of chicken strips potentially contaminated with pieces of metal, following six complaints submitted to the Food Safety and Inspection Service, including three alleged oral injuries. An expanded recall for nearly 12 million