I have no experience with corn gluten, but I believe it's extracted when corn is processed for industrial use, corn sweeteners etc. Dried distillers grain is a refined by-product of ethanol production. It is a cheap enough source of 30 ish percent protein to ship at least 300 miles. It really puts a shine on grass calves over the winter, and fits in any mixed ration. If you can feed it right, it will winter cows. I prefer alfalfa because I think you get more than protein, and I have seen that 5 pounds help fill bellies. I don't know the exact CP, I just see the results.