Michigan had issues 40 years ago when they air dropped hay bales into yarded up deer. The deer quickly ate the hay, but their digestive system didn't have the right "bugs"(?) to digest the hay, and the deer died with bloated stomachs

Yes, as you and Dean have pointed out that can happen if there gut has already switched to woody browse. In the case of Brownville Maine, the deer are fed the native oats early in the winter, beginning in December, and all through the winter so there gut is tuned into digesting the oats and apples. This is also done in Pittsburg, NH, Wilson Mills Maine, etc. The trick is to feed early and completely through the winter. The deer yards are pretty well gone in Pittsburg, NH and in a lot of areas in Maine.

I read an article years ago showing dead deer laying around where someone started feeding them shelled corn late in the winter. Just like mentioned their diet had been twigs and buds, then suddenly changed to corn. I have a deer food plot for fall hunting, we got about 12 inches of snow in late november this year. I took my snowblower and cut a couple of 7 foot wide paths where the clover and turnips etc. were planted. The food was still green. The deer suddenly started coming back to the food plot.

Ed - The incident I described occurred on the Manistee between the 3 C's bridge and Sharon