First off unless your feed is a 12% protein your not adding extra protein your depleting it.
Rolled is only about 12% proteins.
Second, how do you know they like it?
Are they rushing to the feeder and eating the feed down like there starved?
If so that would be because there feed is imbalanced and there not getting the correct nutrition. You see chickens eat to fill a caloric need when that need is met they tend to stop eating, weather or not there full, taken in the correct amount of food or correct amount of nutrition. By adding a somewhat low protein starch to there feed your not only depleting protein but also increasing there caloric intake (starch=calories) and the birds eat less and take in less nutrients.
In short the chickens act like they like the food because there hungry.