Deer in the wild weighing 150 lbs. will eat on average 10-12 lbs per day of forage. That would amount to more than 1 large round bale of hay from April through September. Southern deer will eat more in the winter than Northern deer for the same body size. I raise 100% Northern deer in Louisiana. My does eat feed at the rate of 1.5-2 lbs./hd/day in winter and 4-5 lbs./hd/day in summer with some available forage. Their metabolism slows in winter. In the far North there is less food available in winter. The lower metabolism allows them to survive on less food.
I've been on breeders properties where the deer have no access to anything that isn't fed in a trough. I like mine to have some browse to supplement their feed. Natural browse is impossible to duplicate in a feeder. In winter my deer get alfalfa hay.
Food plots can provide highly nutritious browse. I'll have a combination of wheat/oats/ryegrass in my pens in winter. If your pens can withstand the grazing pressure, a good choice to add to my combination is clover and winter peas. My stocking rate limits my plant choices. In summer I usually plant a sweet Sudan. It grows to about 6' and has a fairly a decent protein content. An added benefit that I believe the deer get from Sudan is when they bed in it there are less insects biting the deer. This is very important during EHD/BT season. Other good warm weather choices that I've had success with in pens with lower stocking rates are chicory, clover, iron and clay cow peas, etc. Depending on soil type soybeans may work better. Any of the legumes that your property can grow will be a very good choice.
I have a custom blended feed fed free choice. My deer will still stand on their back legs to eat leaves and twigs on the trees. They like the feed but they are browsers. They like variety of food choices. They can survive on everything coming from a feed trough but it's not their preference. If you can plant enough to keep up with the grazing pressure, legumes are a very good choice.