Here is what the book says:
Lawfully recovered and possessed parts ? except horns
from bighorn sheep ? may be sold, transferred, purchased or
bartered, when accompanied by a statement on how it was
obtained.
Edible meat from game animals taken from the wild may not be
purchased, bartered or sold.
Recovery, Possession and Sale of Bighorn Sheep Horns:
Horns from bighorn sheep that have died of natural causes
may be recovered and possessed. All bighorn sheep horns
must be presented to Fish and Game for marking with a
permanent pin within 30 days of recovery. It is unlawful to sell,
barter or purchase bighorn sheep horns obtained under these
circumstances, or to transfer ownership of recovered bighorn
sheep horns without a permit from Idaho Fish and Game.