US officials are transferring 33 disease-free bison from Yellowstone National Park to a Montana Indian Reservation as part of efforts to reduce the slaughter of bison that migrate out of the park.

Robert Magnan with the Fort Peck Tribes said a trailer carrying the animals left the park Monday morning.

It was expected to arrive at the reservation in northeastern Montana later in the day.

The shipment includes bison and their descendants that were trapped to prevent the spread of the disease brucellosis outside the park.

They’ve been tested repeatedly to make sure they are disease-free.

Yellowstone has sent thousands of bison to slaughter for disease control over the past few decades.

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