Authorities made what they called the largest cockfighting bust in U.S. history with the seizure of more than 5,000 roosters, hens and chicks from two training grounds, officials said.

Agents found 4,400 chickens Saturday at a 7-acre compound in the Otay Mesa industrial area of San Diego. More than 2,500 birds were seized at the same place six years ago in what was believed to be the nation's largest bust.

Hundreds more chickens were found this time at a second training ground nearby, officials said.

Other stings have resulted in more arrests but none have produced more birds, said John Goodwin, manager of animal fighting issues at The Humane Society of the United States, which deployed its own staff on the raid along with local and federal law enforcement agents.

"In terms of the number of animals seized, this is the biggest, hands down," he said Monday.

Fifty people were issued misdemeanor citations, punishable by up to one year in jail and a $5,000 fine, and ordered to answer to cockfighting charges in early December, said Paul Levikow, a spokesman for the San Diego County District Attorney's office. If the defendants have a history of animal cruelty, they may be charged with felonies.

Another 50 people are still being sought, authorities said.

About 80 percent of the birds seized have been euthanized, Levikow said.

The cockfighting operation was managed and patronized largely by Filipinos, and fights were staged in the San Diego area, Levikow said. Many birds were sent to the Philippines or Hawaii.