I am looking at doing something similar. What I like about the millrun is that it is a digestible fibre energy source; I think it will be easier on the gut than feeding starch energy (ie: barley). As a nutritionist said to me; straw and grain are at opposite ends of the digestion spectrum bacterially speaking. Cows will eat 12-15 pounds of straw free choice, but they may eat more depending on the amount of green; our area has a lot of green this year due to very dry weather and then mid summer rains. It would probably be worth feed testing the straw especially if you think it may have a little better feed value; could save you a lot of money for a $35 test. Oat or 2-row barley straw is the most palatible and nutritious, but again can vary depending on green.