ALBUQUERQUE, N.M. (AP) – Federal officials failed to consider environmental hazards when they gave two companies permission to resume domestic horse slaughter, attorneys for animal rights groups seeking to halt the opening of the slaughterhouses argued Friday.

The Department of Agriculture issued the permits in June, and the plants in New Mexico and Iowa plan to open Monday.

But animal welfare groups are seeking a restraining order from U.S. District Judge Christina Armijo, saying the slaughterhouses should be forced to undergo public review under provisions of the National Environmental Policy Act.

No environmental impact study has ever been done to examine the effects of horse slaughter, Bruce Wagman, a lawyer for The Humane Society of the United States, the Colorado-based Front Range Equine Rescue and other plaintiffs argued in court on Friday. Horses are given more than 100 drugs not approved for other feed animals, he said.

“The government is about to embark on a brand-new multi-state program,” he said. “We just don't know about the dangers that lie ahead.”

But attorneys representing the USDA and the meat companies said the groups presented no evidence to back their assertions that those drugs would pose environmental dangers through waste runoff or other means, arguing the plaintiffs were simply in court because they are morally opposed to horse slaughter and are looking for a way to delay the plants while the lobby Congress for a ban on horse slaughter.

“There is speculation. There is innuendo. But there is no evidence,” said assistant U.S. Attorney Andrew A. Smith.

Congress effectively banned horse slaughter in 2006. But the ban was lifted in 2011, renewing an emotional and divisive national debate over whether horses are livestock or domestic companions, and how best to deal with untold thousands of unwanted, abandoned and often starving horses.

Valley Meat Co. of Roswell, N.M., has been at the forefront of the fight, pushing for more than a year for permission to convert its cattle plant into a horse slaughterhouse. The meat would be exported for human consumption and for use as zoo and other animal food.

After more than a year of delays and a lawsuit by Valley Meat, the Department of Agriculture gave the company the go-ahead in June. USDA officials said they were legally obligated to issue the permits, even though the Obama administration opposes horse slaughter and is seeking to reinstate the congressional ban.

Another permit was approved a few days later for and Responsible Transportation of Sigourney, Iowa.

Pat Rogers, an attorney for Responsible Transportation, said the company was started by three young college graduates looking for a way to help fill a need. Currently, he said, old and unwanted horses have to be shipped thousands of miles in sometimes inhumane conditions to slaughterhouses in Canada and Mexico.

“The truth is, you honor, there is no old horses home,” Rogers told the judge. “There is no Medicare for horses.”

And if the company is barred from opening, he said, the young entrepreneurs will be on the hook for $1.5 million.

Blair Dunn, who represents Valley Meat Co., argued horse slaughter is far from new.

“This has been going on for 100 years,” he said. “... There has never been a finding of environmental harm.”

Horse rescue and animal welfare groups, ranchers, politicians and Indian tribes are divided over what is the most humane way to deal with the country's horse overpopulation.

Some Native American tribes, including the Navajo and Yakama nations, are among those pushing to let the two companies open their slaughterhouses. They say the exploding horse populations on their reservations are trampling and overgrazing rangelands, decimating forage resources for cattle and big game and causing widespread environmental damage.

“The only actual evidence of environmental impact is ours,” said Yakama Nation attorney John Boyd, who filed a statement from the tribe's biologist about the damage from more than 12,000 wild horses on the reservation. “And it's a catastrophe that can be largely or significantly ameliorated” by making it easier for the tribe to round up the animals to slaughter.

While some tribes are opposed to horse slaughter, citing the animals' sacred place in their culture, the Navajo Nation has expressed support for the plants. The Navajo Nation is the country's largest American Indian reservation. A tribal spokesman estimates there are as many as 75,000 horses on its land, including many horses that the officials say are dehydrated and starving after years of drought.

On the other side, actor Robert Redford, former New Mexico Gov. Bill Richardson, current New Mexico Gov. Susana Martinez and New Mexico Attorney General Gary King are among those who strongly oppose a return to domestic horse slaughter, citing the horse's iconic role as a companion animal in the West.