State biologists say as many as 30 of the animals have been found dead south of Darby since pneumonia was first detected in the East Fork herd on Nov. 22.

Fish, Wildlife and Parks biologist Craig Jourdonnais says officials have picked up the carcasses of at least 27 sheep as well as some animals that were so weak from pneumonia that they couldn’t move. One ram with the disease was struck by a car on U.S. 93 south of Darby. Two more found near the highway were so weak they could hardly walk.

Deaths documented so far amount to about 10% of the East Fork herd, and more sheep are expected to die before the disease runs its course.

FWP officials said in extreme cases, as much as 70% of a bighorn herd can be lost, and lamb survival may be suppressed for several years afterward.