(CNN) -- The U.S. Department of Agriculture is investigating "disturbing evidence of inhumane treatment of cattle" at a California meat supplier, the agency said.
After receiving video from an animal welfare group, the USDA sent investigators to the Central Valley Meat Co. and found violations of humane handling, the agency said in a statement.
"We have reviewed the video and determined that while some of the footage provided shows unacceptable treatment of cattle, it does not show anything that would compromise food safety," said Al Almanza, administrator of the USDA's Food Safety and Inspection Service.
The USDA suspended inspections at the Hanford-based company, effectively halting slaughter operations there.
The agency said Wednesday it bought 21 million pounds of beef for federal food programs in fiscal year 2011, nearly one-sixth of its beef purchases.
Company officials have not seen the video, Brian Coelho, president of the Central Valley Meat Co., said Tuesday. He said he was "extremely disturbed" to learn that inspections were suspended.
"Our company seeks to not just meet federal humane handling regulations, but to exceed them," Coelho said in a statement. He said federal inspectors continuously inspect the plant and are able to take action if they see a problem.
"That is why these allegations are both disturbing and surprising," he said.
Central Valley did not respond to a request for comment Tuesday after CNN sent the company a link to the video. The company did not respond to messages left Wednesday.
Compassion Over Killing, a nonprofit organization that focuses on animal cruelty, posted the video to YouTube and to its website on Tuesday. The group said an undercover investigator shot the video.
In the graphic video, one worker stands on the nostrils of a cow that the narrator says has been shot in the head but didn't die right away. In another segment, a worker appears to shoot a cow in the head several times.
"At U.S. slaughterhouses, federal law requires death to be quick, when cows are shot in the head the process should cause immediate unconsciousness," the narrator says. "At Central Valley, countless deaths we documented were slow and agonizing."
Central Valley Meat, a 50-year-old company, was one of the beef suppliers for In-N-Out Burger, a well-known fast food chain predominantly in California and the Southwest. Mark Taylor, chief operating officer for In-N-Out, said the chain has stopped doing business with Central Valley Meat.
"In-N-Out Burger would never condone the inhumane treatment of animals, and all of our suppliers must agree to abide by our strict standards for the humane treatment of cattle," he said in a statement.
The plant has been closed while the USDA conducts its investigation. Central Valley said it will cooperate.
CNN's Jaqueline Hurtado, Tina Burnside and Darrell Calhoun contributed to this report.