For clarification - Digestion of plants and woody matter is accomplished in deer and other ungulates through a symbiotic relationship with the bacteria in their digestive system. Different foods require different bacteria to break it down into particles that the deer can use.

It takes time for the bacteria to change in the deer's system - so new foods should be introduced slowly - or when other foods are abundant. Deer that are stressed (either winter or late summer) are most susceptable to dying due to not being able to digest a new food. It doesn't matter what the"new food" is or how "nutritious" it is - IF the deerdo not have the right bacteria in their digestive track to aid in it's digestion.

There is alot of information on the internet on this topic, if you want to learn more about it - try a google search on "Deer Digestion".

FH