The state attorney general's office filed papers asking the Michigan Court of Appeals to take the case, arguing that Circuit Judge Thomas Solka of Marquette County made errors in his March 24 decision.
A DNR order in 2010 designated exotic swine as invasive species off-limits in Michigan. The agency says they are escaping from game ranches and small farms and ravaging wetlands, streams and farm crops with their rooting and wallowing in the wild.
"With their capacity for reproducing rapidly and inflicting ecological mayhem, feral swine are the terrestrial equivalent of the notorious Asian carp," the state said in its application to appeal.
Several owners are challenging the order, claiming they are being unfairly blamed because their animals are kept in secure enclosures. They say the policy was sought by industrial hog operations to eliminate competition, while supporters of the measure contend feral swine carry diseases that could spread to domestic livestock.
Solka described the policy as so vague that it is unclear which hogs are covered. He ruled it an unconstitutional violation of due process and the separation of powers.
In its application, the DNR said the judge gave undue consideration to a document the agency released in 2011 at the request of an association of ranchers and breeders to explain how officials would determine whether particular animals are pure or hybrid Russian swine.
The document listed physical characteristics such as coat and bristle tip coloration and tail and ear structure, which Solka said could apply to virtually any pig.
But the DNR said that issue was irrelevant because the owners challenging the policy had acknowledged their animals were Russian swine. It also said the judge had incorrectly read the state's order as containing an exemption for Russian boar raised in captivity.
DNR spokesman Ed Golder said Friday the agency plans to withdraw the 2011 document because it "has caused more confusion than clarity." But he said the department stands by the invasive species order and will continue to enforce it.
Joseph O'Leary, an attorney representing the owners, said they were confident Solka's ruling would be upheld.
"We hoped the attorney general would analyze the case on its merits and do the right thing, but the political pressure brought to bear was obviously too much to resist," O'Leary said. "As we have said from the beginning of this case, the DNR's order is an unconstitutional and unconscionable abuse of governmental power."