When deer eat they are feeding themselves, but they are also feeding their gut microorganisms. Deer digestion is 100% dependent on them. They help break down the food, and without them the deer cannot digest. Deer are ruminants, meaning that they bring their food back up to chew it again. If a deer, or any ruminant, starves to the point of also starving off the good microorganisms, in order to survive, the deer will need to get not just food, but needs to get replacement gut flora too. Even with all the food a deer could want, it would starve to death if the gut flora is not replaced.
For their special type of digestion deer have stomachs with four sections, all in a row. The first section, the rumen, is where the food goes first after it has been chewed and swallowed. It can hold over two gallons, and this lets the deer bolt down a large amount of food if necessary so that it can quickly leave an area to return to safety. It is in the rumen that food is held to be brought up into its mouth later for rechewing, this is rumination or "chewing its cud". The food is then ready to go to the second section of stomach, the reticulum. The real digestion takes place in the third section, the omasum. The last section of stomach is called the abomasum, and here the food is pelleted and routed for exit.
Whitetail Digestion
Whitetail Digestion
I take that life if I can, with regret as well as joy, and with the sure knowledge that nature’s ways of fang and claw or exposure and starvation are a far crueler fate than I bestow. – Fred Bear