I eat alfalfa too, and sell some in my shop. But neither me or the cows eat only that: we like to diversify our intake to stay healthy and (global or local) logistic bring us a variety of other food/nutrients.
Sure some cows eat more alfalfa than me but most of them never taste a bit of that and only knows corn, soy and friends.
Some other superplants in the soy/quinoa category to consider: buckwheat and lupinus. Yummy.
The only downside to alfalfa and feeding cows with it is the water usage, but for large parts of the country that aren't California and get decent rainfall, growing alfalfa takes no irrigation. You could maybe also consider the land area needed for it, but US cropland utilization has been dropping for decade after decade and isn't really a concern.