Is it straight DDG? If so, it should be around 30% protein. I've fed DDG mixed with cracked corn for about 10 years now. Don't have any this year yet. I've cut back because of the price which is around $200/ton picked up at the local elevator.
When mixed 50/50 or so with cracked corn the finished mixture is around 14-16% protein. As you have found, once calves get on to it they love the stuff. DDG by itself likes to blow around in the wind. Cracked corn by itself is dusty. I like the way the mixture of both ingredients compliment each other. The cracked corn adds body while DDG adds oil content that cuts the dust of the cracked corn.
You can feed DDG/cracked corn on good clean sod to cows and they clean it up as good or better than cake. Deer and the wild bird population like it too. I've also made my own homemade "lick tubs" with mineral and/or salt. I'd suggest about 10% salt and adjust up or down from there to get your desired consumption along with plenty of available water.
One caution about feeding DDG is it sometimes has high sulphur content. That is because they add sulfuric acid to kill the fermentation process. If your water supply has high sulphur content that could be a problem. My artesian water seems to have high sulphur in it and I have never noticed any problems with my feeding rate. DDG is also is high in phosphorus so you want to feed a low-phos mineral. Faster horses could advise you on mineral needs while feeding DDG. :wink: