It wasn’t The Jungle, Upton Sinclair’s scathing indictment of the meatpacking industry a century ago, but it was the next best thing.

In January 2008, the Humane Society of the United States released a clandestine video showing slaughterhouse workers abusing nonambulatory cows—so-called "downer animals"—at a California facility. The video triggered a massive recall of beef across the United States and brought about major changes in California law. In response to the video, the state legislature imposed strict regulations prohibiting slaughterhouses from buying or processing any downer animal. The law also required that nonambulatory animals be euthanized immediately.

Before the law could take effect, however, the National Meat Association (a trade association representing pork producers) filed a lawsuit in federal district court challenging the regulations. The district court granted a preliminary injunction preventing the new state regulations from taking effect, arguing that California’s law violated the Federal Meat Inspection Act (FMIA). FMIA governs slaughterhouse operations across the country and allows the slaughter of some downer animals. The Ninth Circuit Court of Appeals reversed the trial court in a decision that found no substantial conflict between the FMIA and the more restrictive state law.

The case made its way to the U.S. Supreme Court, which last week ruled that FMIA was the controlling authority after all. The California law, enacted to guarantee more humane treatment for sick and injured animals sent to slaughter, was out of work before it ever took effect.

So What?

If your eyes haven’t glazed over yet, you’re probably wondering why a case about pigs matters in the equine world.

It’s a fair question.

It matters because of the routes the Ninth Circuit Court of Appeals and the Supreme Court took to reach their respective decisions.

The Ninth Circuit relied, in part, on decisions from two other circuit courts of appeals. In Cavel International, Inc. v. Madigan, the Seventh Circuit ruled that a state law banning the slaughter of horses for human consumption in Illinois was not preempted by the FMIA. In Empacadora de Carries de Fresnillo v. Curry, the Fifth Circuit came to the same conclusion about a similar Texas law. The Ninth Circuit reasoned that the FMIA governs meat inspection and labeling procedures at slaughterhouses, but imposes no limits on state regulation of the types of meat that can be processed and sold in the first place.

This is an important distinction for opponents of horse slaughter. If the decisions of the Ninth, Seventh, and Fifth Circuits are good law, states can ban horse slaughter entirely, or impose strict requirements for humane treatment of horses if slaughter is allowed. Given the apparent lack of interest in Congress for a federal ban on horse slaughter, attacking on a state-by-state level may be the only realistic option.

Although the Supreme Court reversed the Ninth Circuit’s approval of the California law, the decision does not directly affect the anti-horse slaughter rulings in Illinois and Texas.

"The Circuit decisions upholding bans on slaughtering horses, on which the Ninth Circuit relied, do not demand any different conclusion," the Supreme Court said. "We express no view on those decisions, except to say that the laws sustained there differ from (the challenged California law) in a significant respect."

That difference, the Court explained, is this: "When such a ban is in effect, no horses will be delivered to, inspected at, or handled by a slaughterhouse, because no horses will be ordered for purchase in the first instance." The California law, on the other hand, addressed treatment of animals after they reached a slaughter plant.

The Illinois and Texas laws banning horse slaughter are safe—for now, at least—and the Supreme Court ruling provides a rudimentary road map for legislatures considered similar laws in other states: An outright ban on horse slaughter probably will stand up to legal scrutiny; attempts merely to improve the conditions for horses (or other animals) at slaughter facilities probably will fail because more permissive federal law will control the slaughter process.

Take this lesson to heart if the legislature in your state is considering equine slaughter.