The plants would become the first horse slaughterhouse to operate in the U.S. since Congress banned the practice by eliminating funding for inspections at the plants in 2006. It restored that funding in 2011, but the Department of Agriculture did not approve the first permits for horse slaughter plants until this summer.
The companies want to ship horse meat to countries where it is consumed by humans or used as animal feed.
Valley Meat owner Rick De Los Santos and his attorney, Blair Dunn, admitted they were surprised when the ruling came down, hours after a temporary restraining order that barred the companies from opening in August had expired.
"I thought the court was headed in a different direction on this since," Dunn said. "I am very, very happy to be wrong."
The Humane Society, joined by the state of New Mexico, filed an almost immediate appeal to the 10th U.S. Circuit Court of Appeals in Denver.
De Los Santos estimated it would be seven to 10 days before he was up and running. But Dunn said Rains Natural Meats, in Gallatin, Missouri, was poised to open as early as Monday.
A third company, Responsible Transportation, which was started in Sigourney, Iowa, by three recent college graduates, abandoned its plan to process horses and converted to cattle after the restraining order was issued in August.