Mercy for Animals released an undercover video claiming to originate from a Foster Farms facility in Fresno, California.

The video shows the workers throwing and punching the animals, and criticises the American Humane Association, which had certified Foster Farms as a humane producer.

Foster Farms has now responded to the allegations, saying in a statement: "Foster Farms has been made aware of an online video showing company employees in Fresno, California, mishandling birds in their care.

"We have already begun a comprehensive investigation to determine the source and location, including a fully cooperative effort with all appropriate authorities.

"The behaviour of the individuals in this video is inappropriate and counter to our stringent animal welfare standards, procedures and policies.

"Since its founding in 1939, animal welfare has always been a top priority for Foster Farms. We believe raising chickens humanely is simply the right thing to do, and we take our commitment to humane values very seriously.

"Foster Farms employees receive annual training in animal welfare policies and the proper handling of birds in their care.

"Any employee wilfully violating Foster Farms’ animal welfare policies and procedures is subject to disciplinary action up to and including dismissal."