An undercover video showing workers at a Colorado pig farm hitting animals with cans and boards has prompted a criminal investigation and the firing of seven employees.

The video, posted online Wednesday by Los Angeles-based group Mercy for Animals, was filmed by one of its members at a Seaboard Foods farm on Colorado's northeastern plains. The group gave it to the Phillips County Sheriff's Office, which launched an investigation and notified Seaboard Foods.

The company supplies pork to Walmart and other retailers. It says the handling of the pigs, which happened while they were being loaded onto trucks, is "unacceptable and inexcusable" and violates its standards. It fired five workers and two supervisors.

Walmart says it doesn't tolerate mistreatment of animals and requires its suppliers to adhere to industry and government standards.