Yes sir feeding it to them.
DE is already used in the feed industry for anti-caking properties.
We Dust our cattle with it and yes we feed it to them. We have no bugs of any kind on our cattle and no parasites when they're processed I always ask the processor to check.
Our cattle have a beautiful shiny coat and no health issues at all...can't say it's all because of DE....but I don't change something unless it broke.
I've also read that it does not work internally but I've also read many articles where they say it does work.
But my opinion is that it's harmless so why not try it internally, worst case is once it comes out in the manure it'll dry out and kill maggots in the manure.
I know for a fact that kills a lot of things because I dust around our barn with it and we find all kinds of dead scorpions, worms and other bugs.