I assure you this is a real phenomenon and not my imagination. Mule deer taken during our August archery hunt, at least the ones NOT from the desert are just fine to eat. I might even try a piece of jerky from the late October hunt but after that and especially in January they are flat nasty. Maybe it is just a regional thing but that mule deer given me by some caribou hunters last summer that was from Montana was pretty rank as well.
