Yellowstone National Park on Wednesday started shipping hundreds of wild bison to slaughter for disease control, as a quarantine facility on a Montana Indian reservation that could help spare many of the animals sat empty due to a political dispute.

Park officials say 15 female bison initially slated for quarantine on the Fort Peck Reservation were instead loaded onto trailers and sent to slaughter. Hundreds more will be shipped in coming days.

More than 400 bison, also known as buffalo, have been captured this winter attempting to migrate out of the snow-covered park to lower elevations in Montana in search of food. More animals are expected to be captured and shipped to slaughter through March.

Fort Peck's Assiniboine and Sioux tribes built their quarantine facility near Wolf Point with enough room for 300 animals in hopes of using it to establish new herds across the U.S with Yellowstone's genetically pure bison.

Tribal Chairman Floyd Azure said state and federal officials "slapped the Fort Peck tribes in the face" by not using the facility.

"They knew we were building a quarantine facility. A lot of money and time and effort were involved in this and all of a sudden they throw a monkey wrench in it," Azure said.

Montana livestock officials oppose transferring bison to the quarantine site because the animals have not been certified to be free of brucellosis, a disease that can cause animals to abort their young. Ranchers in the state fear bison could transmit the disease to cattle and would pose competition for grazing space on public lands.

No transmissions of the disease from wild bison to cattle have been documented.

The park and state severely limit bison migrations into Montana under a 2000 agreement intended to guard against such transmissions.

The agreement also set a population goal of 3,000 bison inside the park. However, there were an estimated 5,500 animals at last count. To reduce that number, park officials want to kill up to 1,300 bison this winter through a combination of slaughter and public hunting.

Hunters in Montana have shot more than 300 bison so far this winter. Meat from slaughtered animals is distributed to American Indian tribes. Many tribes historically relied on bison for food, clothing and other needs until the species was driven to near-extinction during the settlement of the U.S. West in the late 1800s.

Gov. Steve Bullock temporarily halted the park's slaughter plans last month after Yellowstone Superintendent Dan Wenk said 40 animals once slated for the quarantine would be killed to make room in corrals used to hold migrating bison.

Bullock lifted the ban after the park, state and U.S. Department of Agriculture reached a deal that would spare 25 bull bison from the group for future shipment to Fort Peck, once they undergo a year-long quarantine at a federal facility just outside the park. That's now down to 24 animals after one of the bulls was shot Tuesday when he broke his leg inside the park's corrals.

Bullock spokeswoman Ronja Abel said state officials continue to work toward a long-term solution to the issue. She declined to say if that could include future use of Fort Peck's quarantine.

Yellowstone spokeswoman Morgan Warthin said the park still wants to transfer bison to the tribes' quarantine and plans future negotiations with the state to make that happen.

"The ultimate goal is to reduce the amount of slaughter as a first step toward conservation," Warthin said. "Our goal is an operational quarantine, and that includes Fort Peck."

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