Reasons to feed alfalfa

If your horse has ulcers, alfalfa may help reduce the severity. I suspect the high protien content helps. I would still feed an alfalfa-grass mix.

http://www.thehorse.com/ViewArticle.aspx?ID=11596

Hay Fertilization

http://www.thehorse.com/viewarticle.aspx?ID=13655

This is an OK article on fertilization. The article does not say so, but proper fertilization should promote healthy plants. Healthy plants will be nutritious plants. The other thing that is critical to hay quality is timely harvest and hay that is dried without being rained on.