By JESSE J. HOLLAND

Associated Press

WASHINGTON (AP) -- The Supreme Court on Monday blocked a California law that would require euthanizing downed livestock at federally inspected slaughterhouses to keep the meat out of the nation's food system.

The high court ruled that the state's 2009 state law was blocked from going into effect by federal law administered by the Agriculture Department's Food Safety and Inspection Service.

Federal law "precludes California's effort ... to impose new rules, beyond any the FSIS has chosen to adopt, on what a slaughterhouse must do with a pig that becomes non-ambulatory during the production process," said Justice Elena Kagan, who wrote the court's unanimous opinion.

California strengthened regulations against slaughtering so-called "downer" animals after the 2008 release of an undercover Humane Society of the United States video showing workers abusing cows at a Southern California slaughterhouse. Under California law, the ban on buying, selling and slaughtering of downer cattle also extends to pigs, sheep and goats.

But pork producers sued to stop the law, saying the new law interfered with federal laws that require inspections of downed livestock before determining whether they can be used for meat.

The Federal Meat Inspection Act allows a federal meat inspector to examine and then determine whether a downed animal is fit to be slaughtered for meat. It also says states cannot add requirements "in addition to or different than" its requirements.

About 3 percent of pigs that show up at slaughterhouses are non-ambulatory, the National Meat Association says, but veterinarians normally give the non-walking pigs a few hours to determine whether their problem is disease, or just stress, fatigue, stubbornness or being overheated from the trip to the slaughterhouse.

A federal judge agreed and blocked the law, but the 9th U.S. Circuit Court of Appeals threw out the hold. The justices overturned that decision.

Federal law "regulates slaughterhouses' handling and treatment of non-ambulatory pigs from the moment of their delivery through the end of the meat production process," Kagan said. California's law "endeavors to do the same thing, at the same time, in the same place -- except by imposing different requirements. The FMIA expressly pre-empts such a state law."

Copyright 2012 The Associated Press.