I use sweet cob and mineral blocks. In the winter I set out a few bales of alfalfa. Just curious though, do you think its bad for the deer in the middle of winter with not alot of other food around to be eating 100% alfalfa bales? Do you think alfala/grass would be better or does it matter? I feed them 100% alfalfa and they seem fine.
White-tailed deer are primarily browsers (not grazers) and eat very little grass. When you see deer eating in grassy fields they are usually not eating the grass but rather broadleaf weeds (forbs). Grasses are generally low in crude protein and digestibility compared to what deer usually have in their diet.
While cow and deer are both ruminants deer aren't grazers because their digestive system works much faster than cows and would not allow them to benefit much from grasses. However, there are some grasses like ryegrass that are faster to digest and will be used by deer along with other small grains.
For hunting purposes it is highly unlikely that any deer will rely on your alfalfa heavily enough to cause any harm. In addition you are probably providing the alfalfa well before the dead of winter when it could have harmful effects. What is bad for the deer is when well intentioned people try to suddenly feed them alfalfa or corn during the dead of winter after a big storm. By this time the deers digestive system has adjusted to eating low quality browse and most will usually survive these situations just fine without supplemental feeding. In fact, suddenly introduced supplemental feeding can literally result in the deer starving to death despite the fact that its eating high quality food.
Another bad thing would be if someone fed them heavily most of the year and then suddenly cut them off in the middle of winter.
If you feed the deer to no later than 15 December it will not cause issues.