Fly Predators and Diatomaceous Earth

I have recently been given an article that stated if fly predators were used to help keep the fly population down that you should not feed your horses Diatomaceous earth as it would kill the predators.  Can you comment on this?

Also, if this is true, can an internal product like Bug Check,  without the Diatomaceous become available?

We have had many (hundreds) use Bug Check with Predators. A large supplier of such was even suggesting our product at one time along with their predators. Although I haven’t seen them in quite awhile. I can only assume they don’t now because so many realized they didn’t need the predators too? Of course my opinion is that they would only help anyway. 🙂