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

Hundreds more birds were found at a second training ground nearby, officials said.

Many birds were sent to the Philippines or Hawai'i.

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.

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 still be charged with felonies.

Another 50 people are still being sought, authorities said.

About 80 percent of the roosters, hens and chicks seized have been euthanized, Levikow said.