We feed 20%. If we are going to take the time expense and effort I want to try and give them something better than is already out there. During the right times of the year and conditions browse can be really hi protein so no since in shorting them.
When times are hard anything will help them out although I do believe that feed specifically developed for deer is better than that developed for livestock. Although we did fill our feeders with some lactating goat feed when our feed store was out... it was during the summer and we made a lot of jokes about it helping the does out and the deer readily consumed it like anything else we put out... except alfalfa, wont touch the stuff. Talked to a guy at the gas station one day that fed dog food and claimed great results, so who knows.
It's hell eatin em live