A three-judge panel of the U.S. Seventh Circuit Court of Appeals cited measures banning bullfights and cockfights to help explain why it was upholding the law.

"States have a legitimate interest in prolonging the lives of animals that their population happens to like," the panel wrote. "They can ban bullfights and cockfights and the abuse and neglect of animals."

At Cavel International Inc.'s plant, located in the northern Illinois town of DeKalb, about 40,000 to 60,000 horses are slaughtered each year. Except for a portion sold to U.S. zoos, the meat is shipped to be eaten by diners overseas.

The plant has been forced to close twice since late May, when Gov. Rod Blagojevich signed into law a measure banning the slaughter of horses for human consumption, or the import, export or possession of horse meat designated for human consumption.

The plant was allowed to reopen during various court challenges to the law.

It was not immediately clear if Cavel would appeal the latest ruling, or if it would shut its doors Friday night. The company could ask the three-judge appellate panel to reconsider its ruling, or ask the full court to take on the case.