MISSOULA — State game wardens killed three wild bighorn sheep that mingled with domestic sheep near Missoula to prevent them from spreading disease to other wild bighorns.

Fish, Wildlife and Parks spokeswoman Vivaca Crowser says the city of Missoula contracts with a shepherd to graze sheep on land around the valley to control leafy spurge. She said the bighorn rams were in an area they were not expected to be and co-mingled with the domestic sheep before the herder could prevent it.

Domestic sheep can carry bacteria and viruses that can cause fatal illnesses in wild sheep.

Wardens shot the bighorn rams Tuesday afternoon on Mount Jumbo.