A Petaluma slaughterhouse at the center of an international meat recall reopened under new ownership Monday to protests from animal rights activists.

About 30 demonstrators, some wearing bloody aprons and waving signs, converged on the former Rancho Feeding Corp. slaughterhouse to protest what they say is the inhumane treatment of animals at the facility.

Marin Sun Farms CEO David Evans, who assembled a group of investors to purchase the meat plant, is focused on ethically raising and processing meat, spokesman Jeff Bordes said.

"The humane treatment of animals is in line with the principles of this company," Bordes said.

But protesters worried it would be business as usual at the slaughterhouse, despite the change in ownership.

"We thought that the slaughterhouse was going to get shut down and we were going to get rid of one more slaughterhouse," said organizer Lisa Soldavini. "David Evans touts the fact that he is a humane farmer, but we believe there is no humane slaughter."

Demonstrators have staged an annual protest outside the Petaluma facility for the past four years. On Monday, protesters from North Bay Animal Advocates and Direct Action Everywhere carried signs that said "Meat is a Dying Business" and "Don't Buy the Humane Lie."

Organizer Deborah Claassen said it is impossible to humanely kill cattle.

"We felt like the slaughterhouse is spreading a myth," she said. "They are trying to make people think that killing animals is humane. There is no humane way to raise and eat an animal."

Rancho Feeding closed the Petaluma plant Feb. 9 and recalled all 8.7 million pounds of beef processed at the facility in 2013. The U.S. Department of Agriculture accused the company of circumventing inspection rules and processing "diseased and unsound animals." It is being investigated by the USDA, the agency's inspector general and the U.S. Attorney General's Office.

Evans, who founded Marin Sun Farms, purchased the slaughterhouse on Feb. 28 and obtained USDA approval to reopen the facility. He promised a new era of transparency and ethical treatment of animals, saying he reconstructed every system, process and procedure in the slaughterhouse to focus on high standards.

Protesters spent about two hours waving at passing cars along Petaluma Boulevard. Some motorists honked in support while others booed. Afterward, the group held hands in a circle and read poems into a megaphone pointed at the slaughterhouse.

Wayne Hsiung of Direct Action Everywhere said that buying meat is essentially supporting violence.

"Killing is inherently a violent, not humane, act," he said. "The new owner of this slaughterhouse is perpetrating moral fraud on the public."