Alfalfa is a interesting crop, it holds its nutrition value better than any other forage crop when dried, and is somewhat drought tolerant for a legume because of a deep tap root. But it is its high protein content when dried quality that makes farmers plant and store alfalfa as a winter food source for cows and horses. Cows and horses have to eat it because they have no choice, they cannot free range and eat what ever they want like deer. The other benefit to alfalfa is it will store Nitrogen in the soil just like clovers to benefit the next crop.

However .... has a tasty food source for deer, alfalfa is somewhat limited. during periods of new growth after haying the new shoots can attract deer. Deer will eat what ever taste best to them. Once the stems become long and woody the deer don't like it as much. But in the winter when nothing else is availble, deer may dig through the snow to get to what is left.

In general deer will prefer clovers, corn, soybeans more frequently than alfalfa. It's just a matter of what tastes the best in the area to the deer at a certain time of the year.