I add it to the dry food so the chicks get free choice. I put it in the dry dog food too. By ingesting it from what I have researched it eliminates the internal parasites as well as external when you use it as a dust. When they ingest it, it also works it's way out in the pooh, and the flies just won't have anything to do with those DE dallops!
I'm taking a teaspoon a day myself. Just started it but will keep an eye on how my conditions improve. Others have said it works great to regulate stomach and bowel troubles. We shall see.
I am a big believer in DE. I use it everywhere my animals go. And the tick and flea population are near to non-existant for the dogs. When we have rain and the smell in the coop gets stirred up, you know that icky smell, I use the dust and BAM, the smell is gone along with the flies. DE is multi-purpose and WONDERFUL! As long as it's food grade.